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received: 2022–01–11                 DOI 10.19233/ASHS.2022.31
ARCHAEOMETRIC ANALYSIS OF MORTARS FROM THE ROMAN VILLA 
RUSTICA AT ŠKOLARICE (SLOVENIA)
Anthony J. BARAGONA
University of Applied Arts Vienna, Institute of Conservation, Salzgries 14/1, 1013 Vienna, Austria 
e-mail: tonybaragona@gmail.com
Katharina ZANIER
University of Ljubljana, Faculty of Arts, Department of Archaeology, Zavetiška 5, 1000 Ljubljana, Slovenia
e-mail: katharina.zanier@ff.uni-lj.si
Dita FRANKOVÁ
Czech Academy of Sciences, Institute of Theoretical and Applied Mechanics, Prosecká 809/76, Prague 9-Prosek, Czech Republic
e-mail: frankeova@itam.cas.cz
Marta ANGHELONE
University of Applied Arts Vienna, Institute of Conservation, Salzgries 14/1, 1013 Vienna, Austria
e-mail: marta.anghelone@uni-ak.ac.at
Johannes WEBER
University of Applied Arts Vienna, Institute of Conservation, Salzgries 14/1, 1013 Vienna, Austria 
e-mail: johannes.weber@uni-ak.ac.at
ABSTRACT
This paper reports the results of the analysis of mortars used in the Roman villa at Školarice, Slovenia. The 
samples were analysed by optical microscopy (OM), scanning electron microscopy coupled with energy-dispersive 
X-ray spectroscopy (SEM-EDX) and Fourier-transform infrared spectroscopy imaging (FTIR-i). The hydraulicity was 
determined for the ceramic-lime (“cocciopesto”) mortars by chemical dissolution methods, thermo-gravimetric 
analysis – differential scanning calorimetry (TGA-DSC) as well as binder area analysis by EDX and FTIR-i on the 
corresponding thin sections. The results helped in the interpretation of the site especially in relation to the extent of 
use of crushed ceramic as a pozzolanic or waterproofing material.
Keywords: Roman villa, Školarice, historical mortar, FTIR-imaging, hydraulicity index
ANALISI ARCHEOMETRICA DI MALTE DALLA VILLA RUSTICA ROMANA 
DI ŠKOLARICE (SLOVENIA)
SINTESI
In questo contributo riportiamo i risultati dell’analisi di malte della villa romana di Školarice in Slovenia. I 
campioni sono stati analizzati mediante microscopia ottica (OM), microscopia elettronica a scansione accop-
piata con spettroscopia a raggi X in dispersione di energia (SEM-EDX) e spettroscopia a infrarossi in trasformata 
di Fourier (FTIR-i). L’idraulicità è stata determinata per le malte a base di calce e cocciopesto con metodi di 
dissoluzione chimica, analisi termogravimetrica – calorimetria differenziale a scansione (TGA-DSC) e analisi 
dell’area del legante mediante EDX e FTIR-i sulle sezioni sottili corrispondenti. I risultati hanno fornito impor-
tanti spunti per l’interpretazione del sito, in particolare in relazione all’entità dell’uso di cocciopesto come 
materiale pozzolanico o impermeabilizzante.
Parole chiave: Villa romana, Scoladizzi / Školarice, malte storiche, spettrofotometria in trasformata di Fourier 
(FTIR-i), indice di idraulicità
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INTRODUCTION
Background of the Site
The Roman villa rustica at Školarice is located not 
far from the south-western coast of Slovenia on the 
very northern edge of the Mediterranean. During the 
archaeological excavation of the site in 2002, which 
covered a surface area of 6136 m2, several rooms were 
discovered, mostly consisting of the productive part of 
the villa but also including a thermal complex. How-
ever, the area explored represents only a fraction of the 
entire ancient villa complex. Due to the site’s sloping 
terrain the complex was built on terraces descending 
towards the southwest (Figure 1). On the lower, south 
terrace, a small part of the residential area and baths 
were discovered, preserved only at the foundation level 
(Figure 2); unfortunately, large portions of this area were 
removed during construction work in the 1960s. The 
upper terrace was built on sloping levels with a large 
storehouse and rooms used to produce wine, oil and 
possibly even flour. The remains of a torcularium paved 
with coarse mosaic were found here (Figures 3, 4) as 
well. Various open areas used as courtyards completed 
the complex. The villa was erected over an earlier build-
ing towards the middle of the 1st century AD, remaining 
in use until the mid-5th century AD; the development 
of the site is divided into 6 main phases, partly divided 
into subphases (Trenz & Novšak, 2004; Novšak & Žerjal, 
2008; Sakara Sučević et al., 2015; Gutman et al., 2016; 
Žerjal & Novšak, 2020). In ancient times the villa was 
placed in the territory of the colony of Tergeste, within 
the Regio X (Venetia et Histria) of Roman Italy, along 
the Roman road Via Flavia that connected Tergeste 
(Trieste) to Parentium (Poreč) and Pola (Pula). For im-
mediate proximity to the main route of the Via Flavia, 
as also for planimetric reasons (cf. Ventura, 2001), the 
villa appears very likely to have also functioned as a 
mansio (Zanier, 2012, 316). The site is also near to the 
Rižana river and could therefore be tentatively identi-
fied as Aquae Risani”, meaning the ‘Baths of Rižana’, 
perhaps shown on the Tabula Peutingeriana, as “Quaeri” 
(symbolized by a road station with baths) (Degrassi, 
1939, 68; Bosio, 1991, 232); the later Italian name of 
the area is “Scoladizzi” (from Italian scolare, i. e. ‘flow, 
drain’), transformed into Slovenian as “Školarice” (Žerjal 
& Novšak, 2020, 9). 
Damage to the southern terrace, which is the resi-
dential area of the villa, resulted in the extensive loss of 
floors and wall paintings. As a consequence, only a few 
high-quality wall painting fragments with more refined 
decorative motifs, such as those exhibiting stucco 
decoration, were collected during the archaeological 
excavation of the thermal area (Zanier, 2012; Zanier, 
2020). Similarly decorated stucco cornices are typical 
of the final Third and especially the Fourth Pompeian 
Styles of the second half of the 1st century AD (Riemen-
schneider, 1986; Fröhlich, 1995). Across the entire com-
plex plain wall paintings are predominant; they show 
fairly homogeneous preparations characterized by very 
simple decorations including yellow, red, burgundy red, 
green and black panels, sometimes bounded by white 
stripes, as well as white panels bordered by broad red 
bands. These patterns reflect the wide spectrum of plain 
decorations based on chromatic and modular strings of 
panels of interchanging colours, which were especially 
in use from the second half of the 1st through the 2nd 
century AD (Salvadori, 2012).
Previous Relevant Research and Analytical Overview
Paint layer stratigraphy and painting techniques of 
selected wall painting samples were studied previously 
by using optical microscopy, with pigments identified 
via Raman micro-spectroscopy supported by FTIR-i 
micro-spectroscopy and SEM/EDS (Gutman et al., 2016). 
Different tonalities of the red paint layers were com-
posed either by a mixture of red ochre (hematite) and 
yellow ochre (goethite) or by hematite alone. For yellow 
paint layers, goethite was used, for green celadonite, for 
black tones carbon black and for white ones, calcite. 
Paintings were applied in fresco, but details (fillets and 
similar) were applied in secco. Green and red paint 
layers are sometimes applied on yellow underpaint, 
which was probably meant to have positive effects on 
the luminescence of the colour (Gutman et al., 2016, 
201–204). The pigments used and implied technical 
solutions (mixtures of pigments, double colour layers, 
combination of fresco and secco techniques) show that 
skilled artisans were active here (Zanier, 2020). 
The primary tool used for this study of the mortars 
used at Školarice was the employment of a stepwise pro-
tocol of microscopic and micro-analytical techniques 
performed on polished (uncovered) petrographic thin 
sections of 12 of the 19 mortars provided; the remain-
ing 7 were studied by microscopy of cross sections and 
chemical analysis, allowing for correlations to be made 
with the mortars from which thin sections had been pro-
duced. The 12 thin sections were studied in sequence by 
optical microscopy (OM), scanning electron microscopy 
and energy dispersive x-ray spectroscopy (SEM-EDX) and 
Fourier-transform infra-red spectroscopy imaging (FTIR-
i). While these first two techniques are commonly used 
on thin sections, FTIR-i is less, so this research was per-
formed in an innovative manner. Polished petrographic 
thin sections preserve the micro-structural features of a 
mortar, such as the shape and quantity of porosity, relics 
of the binder source and a wide variety of reaction and 
alteration products, and importantly how they relate to 
one another – information that is lost when a mortar is 
analysed by chemical or thermal dissolution techniques 
(Elsen, 2006). Studying these features by image-based 
means is the key to fully understanding both the ma-
terials and methods of the responsible artisan, as well 
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as how a mortar has changed over time (Weber et al., 
2009; Weber & Baragona 2021; Baragona, 2021).
A portion of the mortars described herein utilized 
a reaction between reactive ceramic aggregates (poz-
zolans) and calcium hydroxide to form a hydraulic 
binder through the pozzolanic reaction to produce 
calcium-alumina-silicate-hydrate (“C-A-S-H”) (Mehta, 
1987; Massazza, 2001; Snellings et al., 2012). In the Ro-
man era, these were often used in areas of high humidity 
or in direct contact with water, such as flooring or the 
walls of a bath or cistern (Adam, 1994; Miriello et al., 
2010). These mortars were given special attention, as 
they are particularly helpful in determining/ confirming 
the use of a structure. One means of quantifying a mor-
tar’s binder hydraulicity is its hydraulicity index (HI), 
derived from the formula: SiO2 + Al2O3 / CaO detected 
in a binder, per Boynton’s second equation (Boynton, 
1980; Elsen et al., 2010).  
In our study, this was determined for 5 representative 
samples by 4 different methods: EDX and FTIR-i on the 
Figure 1: Školarice: Roman villa, 2002 excavations (by J. Jeraša, archive Arhej d. o. o.). Red box – thermal 
area, yellow box – production area.
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binder areas of polished thin sections, as well as both 
chemical dissolution and thermogravimetric analysis 
(TGA) of a different portion of the same samples. The 
method using FTIR-i, described further below is a novel 
technique developed during the first author’s dissertation 
work at the University of Applied Arts, Vienna. There-
fore, determining the HI by these 4 different methods 
on the mortar of Školarice provided an opportunity to 
prove the efficacy of the novel technique, in that it gave 
comparable results to the other 3 (see Section 3.5 and 
Table 3) and this probably represents the most important 
contribution of this paper. These results were then cor-
related with similar samples (that were, in the interest 
of economy of time and resources, not prepared as 
polished thin section) from the site to understand where 
and why these types of mortars were used. The paper 
reveals the use of the best mortar for each condition and 
structural need by the builders of the villa at Školarice 
throughout different structures and building phases. In 
doing so, they achieved the high-quality standard of 
construction found throughout the Roman Empire.
MATERIALS AND METHODS
Sample Provenance
For the purpose of this study, 19 samples from dif-
ferent locations and phases of the villa were analysed: 
13 from the thermal area on the lower terrace and 6 
from the productive area situated in the north-eastern, 
higher part of the complex. Samples were selected with 
the aim of including potentially pozzolanic mortars, 
i.e. with visually recognizable ceramic or volcanic 
aggregates and/or a pinkish binder hue. 
Two analysed fragments of painted wall plaster 
(samples Ško-101.1 and Ško-101.2) were found within 
a secondary context of a recent rubble layer extending 
over the lower terrace of the thermal area. They likely 
pertained to its decoration, but it is not possible to de-
fine the specific room of provenance and phase. One 
mortar sample (Ško-310) was sampled in room 4 of the 
thermal area, but in a wall foundation (adjacent to the 
western wall of room 4) pertaining to an earlier building 
that predates the construction of the villa. The thermal 
area has two apsidated rooms (3 and 4) recognizable 
as frigidarium and calidarium (Figure 2). In between, 
there were rooms 5 and 6. The praefurnia were identi-
fied in room 10. To the west of the baths, there is an 
open courtyard (the external western courtyard), which 
was originally paved with irregular stone elements (with 
sizes from 10 x 9 x 3 to 21 x 20 x 7 cm) bound by mortar 
(cf. Ško-284). The thermal area was built in phase 1 in 
the second quarter of the 1st century AD. It was dam-
aged by fire in the first half of the 2nd century AD and 
was after that renovated.
The 1st phase frigidarium basin in the apsis of room 3 
was at that time reduced in size and the original coating 
was replaced by a new mortar layer (cf. samples Ško-
318, Ško-294 and Ško-316). The bottom of the basin was 
probably covered with marble slabs, as can be deduced 
from rectangular imprints in the mortar; the same is valid 
also for the 1st phase basin (imprints and small remains 
of marble elements remain namely also in the 1st phase 
mortar). The calidarium (room 4) was similarly modified 
in phase 2B (cf. Ško-250, Ško-246 and Ško-170). Also 
in phase 2, channel structures in the western part of the 
terrace were built (damaging the original stone paving 
in the external western courtyard, to which sample Ško-
284 relates) and the surface of the courtyard was raised. 
Only small additions and modifications were completed 
in the later phases in the thermal area (Figure 2) (Žerjal 
& Novšak, 2020).
Figure 2: Aerial photograph (by O. Kovač, J. Krajšek, R. Urankar, archive Arhej d. o. o.) and plan (by T. Žerjal, Arhej 
d. o. o.) of the southern part of the villa with the thermal area. 
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Figure 3: Aerial photograph of the north-eastern part of the villa with the productive area (by O. Kovač, J. Krajšek, 
R. Urankar, archive Arhej d. o. o.), the marked location of the torcularium channel (circle, detail in inset) between 
rooms G and L; sample Ško-239 was taken from the mortar bedding layer of the large tesserae mosaic of the 
channel belonging to this torcularium.
Figure 4: Plan of the north-eastern part of the villa with the productive area and an extensive storeroom to the west 
(by T. Žerjal, Arhej d. o. o.), with location of the samples.
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Sample Ško-316 was sampled from the coating plas-
ter of the apsidal basin in frigidarium 3 which was ap-
plied in phase 2B, dated to the 2nd century AD. Ško-318 
and Ško-294 are taken from the mortar of the structure 
made of sandstone elements, composing the bench and 
the border wall of the smaller basin of phase 2B in room 
3. From calidarium 4, but from the same phase, comes 
sample Ško-250, which represents mortar of a built plat-
form (built to level up the 1st phase basin) in the apsis 
of room 4. Next to it a coarse terracotta mosaic, made 
of big rhomboid and trapezoid tesserae (5 x 3 x 2 cm), 
together with its preparatory layers was laid: Ško-246 
is part of the lower, rudus layer (12 to 18 cm thick) and 
Ško-170 of the nucleus layer (10 to 15 cm thick).
The other samples come from the productive area in 
the north-eastern part of the upper terrace, shown in fig-
ures 3 and 4 above. This part of the villa was also built in 
phase 1 during the second quarter of the 1st century AD. 
It consists of an elongated building, stretching east-west, 
with sloping levels towards south. The western part of 
the building consists of a large storeroom with a central 
row of pillars (room SK* in Figure 4). The eastern part of 
the building hosts different units used for the production 
of wine, oil and possibly even flour. Sample Ško-239 is 
from the bedding layer of the large white tesserae mo-
saic of the channel belonging to the torcularium, a wine 
or oil press, located in rooms G and L (dimensions of the 
tesserae: 2,5 x 2,5 x 4,5 cm; dimensions of the tesserae 
on the border of the channel: 6 x 4 x 7 cm –with the 
longest dimensions referring to the vertical embedment 
height) (Figure 3 and inset). This kind of revetment for 
productive structures, such as torcularia is rare, but not 
exceptional, and it was probably also very effective in 
its use. A similar example of torcularium with mosaic 
coating is attested in room 3 of the Roman villa of Russi 
in north-eastern Italy (Mansuelli, 1962; Guarnieri, 2016, 
33–34).
Ško-236 belongs to the mortar bedding layer of the 
opus spicatum pavement in room N which could be 
identified with the lacus, i.e. the must collection basin, 
which could be in that case related to the same press.1
A similar sample is Ško-217, sampled from the 
mortar (3-5 cm thick) covering a low structure in room 
AA, which could also be identified with a productive ar-
rangement or, alternatively, with a simple floor. Sample 
Ško-264 corresponds to the preparatory mortar layer of 
a white tesserae mosaic (tesserae dimensions: 1-1.5 x 
1 x 2.5 cm) in room SS and includes a piece of tessera; 
the mortar layer was 3-4 cm thick and was laid over a 
drainage channel heading south.
North of the building, there was an open courtyard, 
from which water was collected through a drainage 
channel along the northern wall of the storeroom SK*. 
At the very eastern end of this channel, there was a 
stepped structure with steps made of sandstone slabs of 
1 About the Roman wine production method, also from an experimental point of view cf. Indelicato, 2020.
different length, 20-80 cm, and height, 8-12 cm, as well 
as depth, 10-20 cm. This is identified with a stepped 
cascade pertaining to the same water channel, with the 
stepped chutes used for reducing flow velocity (Chan-
son, 2000, 47–48). Mortar from between these steps was 
sampled and analysed (Ško-219). Small interventions 
can be dated to phase 2. In phase 3 (3rd century AD) 
the complex was extended towards east and north, with 
the creation of a porch (room AB) to the north; sample 
Ško-224 comes from the foundation structure of one of 
its pillars. This porch was transformed into two rooms in 
phase 4 (second half of the 3rd century AD), when also 
consistent interventions took place in order to transform 
and divide into several smaller rooms the western store-
room (Žerjal & Novšak, 2020, 26).
Analytical Procedure
Of the samples provided, the 19 that appeared to be 
most representative of the site were selected for further 
analysis. The wide variety of procedures described in 
the following sections was applied in a case-by-case 
manner in order to resolve specific questions, and there-
fore, as Tables 1 and 2 below show, not every sample 
was treated in the same way. The appropriate analytical 
procedure was determined by the (limited) available 
time and resources combined with a philosophical as-
sessment of how much additional information could be 
gained from utilizing the full analytical “toolbox”; e.g. if 
there were two large fraction ceramic aggregate mortars, 
such as Ško-170 and Ško-239, only one was produced 
into a polished thin section and analysed by costly meth-
ods such as SEM-EDX, FTIR-i and TGA. Thus, of the 19 
samples discussed here, the main focus was made on 12 
that were prepared as polished (uncovered) petrographic 
thin sections (shown in light blue in Tables 1 and 2), as 
well as sample Ško-310 prepared as a highly polished 
cross-section. Of these, 5 were selected as an important 
subset (with the analytical procedure shown with bold 
X’s) to which the entire gamut of procedures would be 
applied, answering in particular the questions of level 
of hydraulicity of these mortar samples – an important 
quality in assessing the original intent of the artisanship 
and thus the functionality of the archaeological object.
Optical Microscopy
The preliminary step of mortar analysis typically 
involves a selection from the provided samples in order 
to pick the ones that will tell the most complete story of 
an archaeological site. Often, observation of a mortar 
sample by cutting and visual inspection (referred to as 
“hand section” above) will inform the researcher about 
the future course of analysis. For this site, the samples 
Ško-246, Ško-317 and Ško-318 were observed to not be 
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mortar, but rather large ceramic (-246) or tuff (-317 and 
-318) aggregates with a small amount of mortar attached. 
Because of this, they were excluded from the analytical 
process2. Following this, microscopy was performed on 
the mortars, with the majority of the results being based 
on petrographic examination of 11 of the polished thin 
sections. 
Petrography was performed by a combination of 
2 different optical microscopes. The first was a Nikon 
SMZ 1500 transmitted light, stereomicroscope (SM), 
with an 8x eyepiece, 1x lens, and the ability to zoom 
from 0.75x to 11.25x, for a range of magnification from 
6x to 90x. It includes two attachments: an incident light 
source (with either direct or raking light) and a rotating 
polarizer film. The second was an Olympus BX40 polar-
izing light microscope (PLM) with a 10x eyepiece and 
5,10,20,50 and 100x objectives, for a range of magni-
fication of 50-1000x. Both the incident and transmitted 
light sources are polarizable. With both microscopes, a 
Cannon EOS 600D DSL camera coupled with the EOS 
2 Ško-317 was selected as one of the 12 samples for thin sectioning, both to confirm its nature and to open up the possibility of further 
analysis of the tuff used at Školarice, to be addressed in the conclusions section. 
Utility software was used to capture photomicrographs. 
Preliminary results from optical microscopy allowed for 
the further categorization of the mortar samples (shown 
in Figure 5 below); more in-depth analysis is discussed 
in the following Results sections, which includes the 
estimation of the volumetric binder to aggregate ratio 
(b:a) of each thin sectioned mortar by the application 
of image analysis in the form semi-automatic pixel-area 
counting of pseudo-coloured photomicrographs by the 
Adobe Photoshop® software (discussed in Section 3.3) 
(per Mertens et al., 2009).
SEM-EDX
The second image-based step of the analytical 
protocol employed was the examination of the thin sec-
tions by SEM-EDX. These tools were used primarily to 
understand the chemical nature of areas of interest, such 
as potential reaction rims on ceramic aggregate, and to 
visualize such areas at high magnification. Analysis by 
Table 1: Sample description and preparation.
Sample Name Room/Phase Mortar Type Sample Preparation
Ško-101.1 N.D. Wall Painting Pol. Thin Section
Ško-101.2 N.D Wall Painting Pol. Thin Section
Ško-170 4/2B Cocciopesto Cross Section
Ško-246 4/2B Ceramic Piece, from rudus Pol. Thin Section
Ško-250 4/2B Cocciopesto Pol. Thin Section
Ško-284 7/1 Cocciopesto Cross-Section
Ško-294 3/2B Lime-sand Cross-Section
Ško-303 4/1 Lime-sand Pol. Thin Section
Ško-310 4/ pre-1 Cocciopesto Cross-Section
Ško-315 6/1 Lime-sand Pol. Thin Section
Ško-316 3/2B Cocciopesto Pol. Thin Section
Ško-317 5/1 Tuff Piece, from stone paving Pol. Thin Section
Ško-318 3/2B Tuff Piece, from structural mortar Hand Section Only
Ško-217 AA/1 Cocciopesto Pol. Thin Section
Ško-219 A/1 Lime-sand Pol. Thin Section
Ško-224 C/3 Lime-sand Pol. Thin Section
Ško-236 N/1 Cocciopesto Cross-Section
Ško-239 G-L/1 Cocciopesto Pol. Thin Section
Ško-264 SS/1 Cocciopesto Hand Section Only
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EDX was of particular importance to perform oxide per-
centage analysis of relic lime clasts in order to determine 
the source of lime binder, as well as to determine the 
level of hydraulicity of the mortars’ binder matrix. For 
the latter, both area and point by point measurements 
were made in order to determine the relative proportions 
of silica plus alumina oxides to calcium oxide (SiO2 + 
Al2O3 / CaO), this is shown as a percentage and referred 
to as the “hydraulicity index” (HI) (Boynton, 1980, Elsen 
et al., 2010). This is the first of four methods by which 
the HI was determined (see Table 3, Section 3.5). The 
device used for this work was a FEG Quanta 250 Scan-
ning Electron Microscope (FEI, U.S.A.) coupled with a 
Pegasus APEX Energy-Dispersive X-ray spectroscope 
(Ametek EDAX, U.S.A.) equipped with the Genesis 
SEM Quant software (SEM-EDX). Images were generally 
taken in back-scattered electron mode (BSE) at 20 kV 
with a spot size of 3.5-4.0 nm and a working distance of 
between 12-15 mm. EDX measurements were typically 
quantified by oxide analysis (omitting carbon, heavily 
prevalent in the epoxy resin), so that results are to be 
understood to represent the proportion of one oxide to 
another in the target area.
Fourier-transform Infrared Spectroscopy Imaging 
(FTIR-i)
The final step of the image-based analysis protocol 
relied on using FTIR-imaging to map the area cor-
responding to cement hydrates in the polished thin 
section, in this case calcium-aluminosilicate-hydrate (C-
A-S-H) resulting from the pozzolanic reaction (Mehta, 
1987). The target spectra for defining these molecules 
correspond to the detection of carbonates (CO3; stretch-
ing around 1350 cm-1 to 1500 cm-1, silicates (Si-O 
stretching between 1100 and 950 cm-1 and a hydrate 
band at ca. 1660 cm-1 indicating the interstitial bound 
(or “crystal”) water of C-A-S-H (Baragona et al., 2019a; 
2019b; Baragona, 2021; Diekamp et al., 2010; Farcas 
& Touzé, 2001; Horgnies et al., 2013; Hughes et al., 
1995; Paama et al., 1998; Yu et al., 1999); the detection 
of these species at the same locations in the mortar are 
taken to indicate co-molecularity (ibid). By selecting 
these bands, the software automatically displays the 
distribution of the intensity of such bands across the 
entirety of the image. A colour scale from red (strong) 
to blue (absent) indicates the distribution of the selected 
bands, which corresponds to the distribution of chemi-
cal species. Combining this information with a scaled 
image of the mortar creates a pseudo-coloured image of 
the mortar thin section from which pixel-counting can 
again be used, this time to determine the percentage of 
the surface area of the mortar’s binder in which C-A-S-H 
is detected, thus the volumetric content of C-A-S-H in 
the binder matrix, a direct visualization of a mortar’s 
hydraulicity (Baragona et al., 2019a; 2019b). Put simply, 
this step combines detection by FTIR-imaging (Yu et al., 
1999; Diekamp et al., 2010) with image analysis tech-
niques (Mertens et al., 2009) by way of comprehensive 
imaging. This is the second way by which the hydraulic-
ity index was calculated (see Table 3, Section 3.5), and 
is illustrated in Figure 6 below. 
The device used was a Nicolet iN 10 MX Infrared 
Imaging Spectrometer (Thermo-Fischer Scientific, USA), 
with cooled MCT-A linear array detector, and interfaced 
with OMNIC Picta software. Spectra were collected in 
reflection mode, spectral range 4000-720 cm-1, aperture 
25 µm, with 8 cm-1 spectral resolution, and spatial reso-
lution <10 µm. Normal mapping mode was used with 
a 2 second collection time per step. The spectra were 
finally vector normalized and baseline corrected.
Chemical Dissolution per RILEM TC-167
Traditional, laboratory-based mortar dissolution 
testing was performed in parallel to the image-based 
analysis, in a large part to determine if there was a 
correlation between results gained by both methods. 
Two test procedures from the RILEM technical commit-
tee publication on the characterization of old mortars 
(TC-167-COM Sections 2.1.1 and 2.1.1.3, Method 
2) were selected to characterize the archaeological 
mortars (Middendorf et al., 2005). First, the mortar 
was dissolved in hydrochloric acid, separating the 
binder from the aggregate, thus defining the binder to 
aggregate ratio gravimetrically (see Table 4). Second, 
the quantity of soluble silica was determined by treating 
the remnants of the previous test with a boiling alkali 
solution, which separates the hydraulic phases from the 
remaining mortar components. The results of this test 
are also expressed gravimetrically (see HI Table 3) and 
represent a third method of determining the HI (soluble 
silica as a percentage of the total soluble binder). These 
two sets of results were refined by testing the aggregate 
separately from the mortar, to determine the aggregates’ 
solubility in acid and alkali. While these dissolution 
tests provide gravimetric data, the image-based analysis 
provides volumetric data, which will be considered 
when drawing conclusions from these data sets in the 
Results Section 3.5. 
Thermogravimetric Analysis
Thermogravimetric analysis (TGA) is a common method 
used to study historical mortars, in particular to analyse the 
binder content (Paama et al., 1998; Bakolas et al., 1998; 
Drdácky et al., 2013; Moropoulou et al., 2000; 2004); it 
was the fourth method by which the HI was determined for 
this work. This method allows for both the identification 
and gravimetric quantification of various contents of the 
mortar. The components typically measured are free water 
until 105 °C, bound water and organic material between 
150-600 °C and calcium carbonate starting at 700 °C. 
The identification/ quantification of C-A-S-H is related to 
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Figure 5: Photos and hand-sample images of the mortars discussed (excludes wall painting and non-mortars). 
A-E: Ško-170, Ško-217, Ško-239, Ško-284; Ško-250; F-I: Ško-264, Ško-236, Ško-310, Ško-316; J-N: Ško-219, 
Ško-224, Ško-294, Ško-303, Ško-315 (field photographs: Arhej d. o. o.).
Figure 6: Illustration of the FTIR-imaging technique to determine mortar binder content, per Baragona 2019; 2021. 
Left to Right: A) SM, transmitted light, darkfield mode image of a cocciopesto mortar (Ško-316); B) FTIR-image of 
the same mapping the co-molecular carbonate (wavenumber 1410 cm-1) and silicate (wavenumber 955 cm-1) likely 
indicative of C-A-S-H, note distinctive occurrence at aggregate rims; C) Scaled composite image with peak inten-
sities of the images wavenumbers superimposed over the SM image from 1); D) Detail of area of binder imaged 
through FTIR-i, scaled with background removed for automatic pixel counting to give a surface area percentage, 
calculated as a percentage of the surface area of the binder given in the HI results below.
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the detected bound water content (ibid.). Components 
can be identified by the temperature at which they leave 
the system, signified by “peaks” in the thermograph cor-
responding to the weight loss their leaving causes. Because 
there can be overlap between peaks, there is some room 
for interpretation by the operator, however there is often 
the additional confirmation by mass spectrometry.
Five of the archaeological specimens (Ško-217, Ško-
239, Ško-250, Ško-310, Ško-316) were gently crushed 
in a porcelain mortar and sieved through a 0.063 mm 
sieve to separate the binder from the aggregates before 
analysis. The rich-in-binder fraction was subjected to 
thermal analysis. Thermal analysis was performed using 
a TA Instruments Discovery SDT Q650. Approximately 
20 mg of the sieved fine fraction of the sample was 
placed in alumina pans. The analysis was performed in 
a nitrogen atmosphere within the temperature interval 
from 25 to 1000°C with a temperature gradient of 20°C 
per minute. The calcium carbonate content and water 
bound in hydrated phases (CSH, CAH), was quantified 
as interpreted by the Universal Analysis 2000 software. 
The results were converted into a percentage (weight loss 
by dehydration of hydrated phases/ total binder weight 
loss = weight loss hydrated phases + carbonated phases 
= decimal result *100 for percentage) for comparison to 
the HI results given by the three other methods; most 
importantly to correlate to the results given by FTIR-
imaging in combination with digital image analysis on 
the same 5 samples (Results Section 3.5).
RESULTS
The thirteen samples examined scientifically fall 
into one of 3 types: finish or decorative mortar (samples 
101.1, 101.2, 303 and 219), structural mortar (samples 
217, 224, 239, 310, and 315) or waterproofing mortar 
(samples 250 and 316), while samples 246 and 317 
proved to not be mortar. Many samples include ceramic 
material, which could generally be considered a poz-
zolan or reactive aggregate; these are samples 217, 224, 
239, 250, 310 and 316 of the structural and waterproof-
ing mortars as well as the base “rough coat” of the wall 
painting fragments sample 101.1. The two waterproofing 
mortars show a much finer fraction of ceramic material. 
This would have produced a more strongly hydraulic 
mortar and perhaps a smoother (and therefore more aes-
thetically pleasing) finish. Samples 170, 264 and 284, 
although not analysed scientifically, would appear to be 
most similar to the ceramic-bearing structural mortars in 
terms of composition and application. The imagery and 
discussion in the following Sections 3.1-3.4 describe 
all of the mortars analysed in a comprehensive way, 
Section 3.5 that follows provides multi-analytical data 
pertaining specifically to the level of hydraulicity found 
in 5 cocciopesto mortars, and what this information 
implies for the interpretation of the site in terms of its 
construction and archaeological history.
Lime Binder and Relict Clasts
Large, partially burned pieces of calcareous stone 
can be found throughout the samples; it can be reason-
ably assumed that these are remnants of the source stone 
for the lime (“relict lime clasts”) (Hughes et al., 2001). 
Evidence of calcination is shown by PLM as areas where 
there is undispersed lime near relic lime clasts (Figure 9, 
C, D), or nearly fully burned relics that preserve some 
micro-features of the original stone (Figure 7, Right). 
These are predominately marble, which is not locally 
available, but was apparently used as lime source stone 
from the 1st building phase onwards and also in the 
wall mortar sample 310 of the structure predating the 
construction of the villa. All of the cocciopesto mortars, 
the sand-lime mortar samples 219, 224 and 294 as well 
as both wall painting mortars contain these marble rel-
ics (although 294 appears to have both these as well 
as limestone relics). The marble used in the intonaco 
layers of the wall painting fragments (samples 101.1 
and 101.2) matches this marble as well, both optically/
structurally (by OM – Figure 7) as well as chemically 
(by EDX). Samples 303 and 315, pertaining to phase 
1, appear to have a different source of raw material, a 
sandy limestone, which may be of local provenance. It 
is interesting to note that the cocciopesto mortars from 
this and later construction phases use marble as the lime 
source stone, while these sand-lime samples appear to 
have a different source.    
In all cases except for the wall painting fragments, 
the presence of large, undispersed lime lumps can be 
seen as evidence for a “hot” or rapid slaking technique 
(Pintér et al., 2011; Weber et al., 2013; 2014). For Ro-
man era cocciopesto or pozzolanic mortar a “basket 
slaking” technique was often employed that would 
leave these lumps as well (Adam, 1994; Hughes et al., 
2001; Elsen, 2006; Baragona, 2021). The intonaci of the 
wall painting fragments lack lumps indicating the use 
of lime putty. Only two samples (219 and 303, again 
pertaining to phase 1) contain pieces of charcoal (lime 
production fuel residue), indicating generally thorough 
sieving of the quicklime after production, a clean burn-
ing wood, or both. The wood species appears to be a 
softwood (conifer). Preliminary EDX results of both relic 
lime clasts and undispersed lime lumps reveal a nearly 
pure (95%+) calcium carbonate composition, again 
with the exception of samples 303 and 315 in which the 
sandy limestone relics could include up to 15% silica 
and alumina by oxide percentage. The limestone was 
not found to be dolomitic. Additional photomicrographs 
of the lime binder source stone are shown in Figure 8.
Aggregates and Classification
Petrographic examination of the 12 thin sections 
allowed for the classification of the mortars, which as 
presented was done by aggregate type, but could have 
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also been done by mortar function. The former method 
was chosen to help frame the later discussion regarding 
binder hydraulicity (of the cocciopesto mortars) found 
in Sections 3.5 and the Discussion. Grouped this way, 
there were four cocciopesto mortars and four sand-lime 
mortars; the remaining four thin sections consisting of 
the two wall-painting stratigraphic mortars and two 
“non-mortars” are discussed in following sections. 
In four of the samples (217, 239, 250, 316) plus the 
base layer of sample Ško-101.1, the predominate ag-
gregate is ceramic material (see Figure 9A-D, K). Low 
burned ceramic material was commonly used in Roman 
times as a pozzolan to create a mortar that was both 
durable and had the ability to set in moist environments, 
per Vitruvius (Secco et al., 2018; also see Vitruvius 
II.5.1). Larger pieces of ceramic were often used in sub-
flooring, such as a hypocaust or in sample 239 (Figure 
9B), a preparation layer for a mosaic drain channel of a 
torcularium press, dated to phase 1. The ceramic mate-
rial itself appears in two different colours, reddish and 
yellowish (sometimes greenish because of intrusion of 
the blue dye). This is more likely due to differing firing 
temperatures rather than different clay sources, as EDX 
shows a similar oxide composition throughout, and SEM 
shows similar microfeatures in all samples. Sample 224 
also shows a large piece of ceramic perhaps used to help 
fill a crack in the surrounding masonry as the mortar 
itself is composed of sandy aggregate, as well as a few 
loose foraminifera (Figure 9F).   
At Školarice, cocciopesto mortars were used in a 
wide variety of applications. Samples 250 and 316 (Fig-
ure 9C, D), both pertaining to phase 2B, i.e. a renovation 
phase (following fire), but from two different rooms of 
the thermal area, contain mostly finely graded ceramic 
aggregate and were applied as bedding, waterproofing 
or a rendering coat; of the samples not prepared as thin 
sections, number 310 (Figure 9H above) is of similar 
composition. The remaining samples include a wider 
range of ceramic sizes and appear to have more of a 
structural application (as a flooring or subflooring mor-
tar), such as the previously mentioned sample 239, and 
the analogous (non-thin sectioned) samples 170, 236, 
264, and 284 shown in Figure 5 A, D-F. The connection 
between the ceramic grading, their application and their 
Table 2: Analysis performed by sample. Blue-highlighted samples used in Table 3.
Sample Name OM SEM-EDX FTIR-i Chem.-Diss. TGA-DSC
Ško-101.1 X X
Ško-101.2 X X
Ško-170 X X X
Ško-246 X X
Ško-250 X X X X X
Ško-284 X X X
Ško-294 X
Ško-303 X X X
Ško-310 X X X X X
Ško-315 X X
Ško-316 X X X X X
Ško-317 X X
Ško-318 X
Ško-217 X X X X X
Ško-219 X X X
Ško-224 X X
Ško-236 X
Ško-239 X X X X X
Ško-264 X X X
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apparent binder hydraulicity is discussed in Section 3.5 
below.  
The remaining non-wall painting samples are com-
posed of sand-lime mortar; the sand is composed of 
both silicate and carbonate material and the angularity 
is typical for sand coming from a small river. The ag-
gregates appear to be nearly all the same size, (“well 
sorted”), but it is not clear if this is the result of sieving 
or was natural at the source (Figure 9E-H). 
Samples 101.1 and 101.2 (Figure 9K, L) are wall 
painting fragments found at Školarice, but cannot be 
associated with a specific building phase, as they were 
found within rubble layers in the thermal area. Sample 
101.1 is a mortar of at least 6 layers (rough coat, 2 arric-
cio layers and 3 intonaco layers in which the final finish 
was white. A 6th lime wash layer is at the top surface, 
blended with the final intonaco layer composed mostly 
of lime with small fragments of marble. This is followed 
by 2 more layers of lime-marble intonaco, with the ag-
gregate size quickly increasing. The sample broke during 
preparation, not along the intonaco–arriccio boundary, 
but rather through an arriccio layer. The base layer is 
highly porous and composed of a mixture of ceramic 
material with some large calcareous pieces, perhaps 
unburned lime source stone. Sample 101.2 consists of at 
least 3 layers. The lack of ceramic material in the base 
layer indicated that this wall covering was probably 
not in a room that maintained a moist environment, 
although it is possible the sample does not include all 
layers. The top intonaco layer was coated with a layer 
of yellow ochre. Large lime lumps are prevalent in the 
lower layers.  
Figure 7: Školarice Intonaco, Lime Source Stone Left Image: Marble fragments used in the middle intonaco layer of 
sample Ško-101.1. While smaller fragments (a.) may indicate the use of sparite, the larger, polycrystalline fragment (b.) 
contradicts this. (c.) shows a weathering frontier around another multi-crystal fragment, indicating the marble’s expo-
sure before (likely) reuse. Right Image: Large marble fragment in the binder of sample Ško-239 (a.) and corresponding 
partially burned lime relic clast (b.) with corresponding large grain boundaries indicative of the original cleavage. Both: 
PLM-Trans. Light, crossed polars.
Figure 8: Školarice Lime Lump Examples Left to Right: A) Marble relict, sample 219 (lime-sand mortar); B) Marble 
relict, sample 250 (cocciopesto mortar);C) Marble relict with attached undispersed lime containing brick dust, sample 
316 (cocciopesto mortar); D)  Sandy limestone relict with undispersed lime above, sample 315 (lime-sand mortar); all) 
PLM-Trans. Light, crossed polars.
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Finally, samples 246 from the rudus layer in room 
4 (Figure 9I) and 317 from the stone paving in room 5 
(Figure 9J) represent examples of what are likely pieces 
of fill with small amounts of mortar attached, 246 domi-
nated by a large piece of ceramic and 317, a large piece 
of tuff. Although they were not examined in detail, 246 
may simply be a fragment of a structural mortar with 
a large, apparently unworked ceramic aggregate, and 
317 may be of further interest since tuff is not a locally 
sourced stone. It appears to be a piece of an ashlar, 
rather than added as an aggregate, and does not appear 
to be pozzolanically active (and is not a small enough 
grain to be so).
Binder to Aggregate (b:a) and Porosity Results
Pseudo-colour images of photomicrographs of a rep-
resentative area of each mortar prepared as a polished 
thin section were analysed by point-counting in image 
editing software (Adobe Photoshop) in order to deter-
mine the binder to aggregate ratio (b:a) and porosity (by 
volume) as described in Section 2.2.1 above; the b:a 
was also determined gravimetrically through chemical 
dissolution as a comparison as described in Section 
2.2.4 above. Examples of images produced this way are 
shown in Figure 10 below. The results of this analysis 
are given on a sample by sample basis in Table 4 in the 
Summary below, but in general there was little differ-
ence in b:a between mortar type, regardless of analysis 
type. The cocciopesto mortars have volumetric b:a 
ranging between 2:3 to 2:1 (40%-67% binder, average 
52%, standard deviation of 13.5%), while the sand-lime 
mortars have a b:a ranging from 3:5 to 2:1 (37.5%-67% 
binder, average 48%, standard deviation 14%). The 
gravimetric results are similar with average b:a of 54% 
(Std Dev. 17%) and 45% (Std Dev. 6%) for mortars with 
ceramic or sand as aggregate, respectively.       
The porosity as determined by image analysis was 
more divergent; the average porosity of sand-lime mortar 
was 8% (range 2–14%, Std Dev. 5.6%), while the average 
porosity of cocciopesto mortar was half as much at 4% 
(range 1.6%–7.1%, Std Dev. 2.6%). Thus, while both 
mortar types used a similar amount of lime binder, the 
cocciopesto mortars were found to be more compact.  
Figure 9: Školarice Petrographic Images: stereomicroscopy (some in dark-field mode) and polarizing light 
microscopy with descriptions as in the text below.
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SEM-EDX RESULTS
In general, the SEM was used sparingly for analysis of 
this archaeological site; the EDX function proved to be 
more useful in determining or confirming the chemical 
composition of relic lime clasts and lumps, as well as the 
content of the binder matrix. The results of the former (lime 
lumps) have already been discussed in Section 3.1 above, 
while the discussion of the oxide content of the binder 
matrix will be discussed in Section 3.5 below. Figure 11 
below displays images that show the utility of the SEM.
In the first two images (Figure 11A, B), more detail 
is gained on the nature of the wall painting mortars, 
such as determination of stratigraphy and identification 
of pigments. In Figure 11A there is a clear carbonation 
line between the last layer of intonaco and a layer of 
whitewash. The large bright objects in Figure 11B are 
the yellow ochre pigment particles visualized. Figure 
11C confirms the presence of the product of the poz-
zolanic reaction, displaying small relics of C-A-S-H 
(needle-like growths) in the crack of an undispersed 
lime lump, while Figure 11D highlights a (rare) piece 
of fuel residue. Figure 11E shows a phenomenon that 
was so unique and noteworthy that EDX mapping was 
used to investigate the formation of magnesium silicate 
hydrate, as described further in Figure 12 below. Figure 
11F shows a detail of the weathering rim on a piece of 
marble used in the intonaco for Ško-101.1, indicating 
that the marble used for both this layer and the lime 
source for many of these samples was likely recycled 
(hence the weathering front indicating previous usage/ 
exposure). The last two images (Figures 11G, H) show 
Figure 10: Examples of a cocciopesto (above) and sand-lime (below) mortar as pseudo- coloured for b:a and 
porosity quantification.  
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what can be misconstrued as a reaction ring on a piece 
of ceramic, but closer inspection shows it to be an area 
where lime binder has compacted in the space near the 
rim of a ceramic piece without reacting with it.
Figure 12 shows an area of Ško-239 that by petro-
graphic examination, presented itself as a strange, glassy 
area of the binder near a large piece of ceramic aggre-
gate (as shown in the cross-polarized photomicrograph 
in this figure. This area was further examined using EDX 
mapping when point analysis indicated the presence of 
large amounts of magnesium, but no calcium (or silicon) 
was present at this location. Although only one example, 
this area could be the remnants of part of a binder sys-
tem composed, at least in part, by magnesium-silicate 
hydrate, a binder (by-)product of recent scholarly 
interest when found in Roman-era mortar (Secco et al., 
2020). Since the lime source stone used in the mortar 
was not found to be dolomitic, and it can be assumed 
that seawater was not used in its slaking, the source of 
the magnesium, and if this can be found elsewhere on 
the site is a source of potential further study.
Multi-analytical Results Determining the Hydraulicity 
Index
Special emphasis was given to the determination 
of the degree of hydraulicity (in this case, pozzo-
lanicity) of five of the mortars found at Školarice in 
order to examine if particular structures had been 
built with the need for particularly strong or wa-
terproof mortars in mind, since the type of mortar 
employed by ancient builders gives evidence of their 
intent for the structure in which it was employed. In 
the context of ancient Roman sites, the addition of 
ceramic to lime mortar was used in a wide variety of 
applications to improve the qualities of the mortar 
(Vitruvius II.5.1; VII.1.3; VII.4.1), taking advantage 
of the pozzolanic reaction to create a hydraulic 
mortar. Although the reddish hue of the binder of 
these mortars is taken as empirical evidence that this 
was done, and indeed as evidence of pozzolanicity, 
the steps outlined in Sections 2.2.2-2.2.5 above 
were performed to provide correlative, quantitative 
Figure 11: Various phenomena visualized in greater detail by SEM, as described in text.  
Figure 12: EDX mapping results (left two images) for a magnesium-rich, calcium-poor area of the binder 
in sample Ško-239.
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evidence of the pozzolanicity/hydraulicity of these 
mortars, referred to herein as their hydraulicity index 
(HI). Thus, were EDX, FTIR-i, chemical dissolution 
and thermal gravimetric analyses made of the binder 
of these five mortars, with the results given in Table 
3. The data for the 5 samples are generally consistent 
based on all four analytical procedures, with the 3 
examples with more finely graded ceramic mate-
rial having on average, a higher hydraulicity index. 
Except for sample 217, all could be described as 
moderately hydraulic, which in the case of 239, from 
the torcularium channel, is somewhat unexpected 
given the dearth of visible small aggregates. As for 
217 the low hydraulicity index could be important 
for determination of the function of the mortar and 
structure to which it belonged, as it was not clear 
from the archaeological context. Possible interpreta-
tions include either a productive arrangement or a 
raised floor structure, with the latter option as more 
plausible in light of the analytical results presented 
herein. In relation to 250 and 316, hydraulicity was 
expected because of the archaeological context of 
the thermal area they come from. This was not the 
case for sample 310, which came from the wall of 
an earlier building predating the construction of the 
villa. Since very little remained of this structure, any 
additional information, such as the use of a hydraulic 
mortar is therefore very precious and can be useful 
for its further interpretation. Figure 13 shows the 
clustering of results by sample, with the EDX and 
FTIR-i results having the strongest correlation and 
TGA as a clear outlier. There is no difference in ob-
served hydraulicity between the samples of different 
building phases, although this assertion would ben-
efit from the analysis of a larger number of samples.
DISCUSSION
Concluding, 19 mortar samples were analysed, 
12 prepared as polished petrographic thin sections. 
These came predominately from 2 building phases, 
but from different types of structures. Samples were 
selected with the aim to include mortars with ce-
ramic or pozzolanic aggregates, with hydraulic fea-
tures: they were chosen by macroscopic inspection 
based on their pinkish colour or observable reddish 
and blackish grains. Analytical results revealed that 
macroscopic identification is often not reliable. For 
example, sample 239 has a higher hydraulic index 
than sample 217, even though the former displays 
only large ceramic inclusions and whiteish binder, 
yet was still found to be moderately hydraulic, while 
the latter is pinkish with fine ceramic aggregate 
present. Sample 317, as well as others not included 
in this work, include tuff, but show no reactivity, 
hence are not pozzolanic. 
A summary of the results of this analysis is given 
in Table 4 below. Overall, they are remarkable 
for their consistency with typical Roman building 
materials and practices of the era. There are several 
findings that illustrate this. Firstly, the use of marble 
for both the intonaco layers of the wall painting 
fragments as well as its (re-)use as the predominate 
source stone for the production of quicklime in 
all types of mortars, despite the fact that there is 
no locally available marble, while limestone can 
be found in the region. This implies the import of 
marble specifically for this use or its recycling from 
previous, earlier structures, from the site or sur-
roundings. The latter option is still more interesting, 
considering that small portions of an older building 
predating the construction of the villa were found 
in place. In the mortars of the 1st phase, it appears 
that marble was burned for quicklime, but only used 
in cases when it would be combined with ceramic 
material to make a pozzolanic mortar; those using 
sand aggregate appear to use quicklime calcined 
from local limestone (see Figure 8 above). This 
adheres generally to the rule laid out by Vitruvius 
that harder stone should be used for mortars used 
in structural applications (Vitruvius II.5); the lesser 
presence of marble in the 1st phase implies that the 
material was in this early phase hard to acquire, but 
was nevertheless selected for structural uses that 
required waterproofing as well. This leads to the 
second point, that in both most investigated phases 
(1 and 2B), particular care was taken to produce a 
robust waterproofing material when making floor-
ing (samples 217, 239) or waterproofing mortars 
(samples 250, 316); this was not done in samples of 
structural mortar used outside (sample 315). 
As to the methodology used in determining these 
conclusions, the petrographic and scanning elec-
tron microscopic images speak for themselves; the 
ability to determine conclusive, correlative results 
that identify mortar constituents and their relation to 
one another is the primary advantage of the study of 
thin sections (Elsen, 2006; Baragona et al., 2019a; 
Table 3: Hydraulicity index results by technique.
Sample 
Name
HI by: 
Chem.
HI by: 
EDX
HI by: 
TGA
HI by: 
FTIR-i
Ško-217 .08 .09 .16 .06
Ško-239 .21 .25 .20 .20
Ško-250 .13 .22 .25 .15
Ško-310 .21 .30 .16 .25
Ško-316 .25 .50 .21 .31
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2019b). Comparing the two methods of determining 
the binder to aggregate ratio (detailed in 3.3 above) 
proves that the method of using pseudo-colouring 
thin section micrographs is a good analogue for the 
results found by chemical dissolution, while one 
should use caution when comparing gravimetric to 
volumetric data; the results given in Table 4 show 
values that are similar enough to support this asser-
tion (i.e. there is never a case where the values are 
drastically different).
The novel technique of using scaled FTIR-image 
results to determine the hydraulicity index of ar-
chaeological mortars shows similarly promising re-
sults. The results of the methods given in 3.5 above 
are compared by means of a scatter chart in Figure 
13 below, where the results of analysis of 5 selected 
ceramic-lime (theoretically pozzolanic) mortars by 
the four complimentary methods are shown, listed 
from left to right by sample with the highest ob-
served average hydraulicity index. Clustering the 
results shows that by and large, the techniques are 
comparable, e.g. all 4 methods show sample 217 
to be the least hydraulic and 316 to be the most 
hydraulic, with the others falling in between when 
the values given by each technique are averaged. 
Thus, they are likely to be interchangeable in terms 
of determining how hydraulic a mortar is relative 
to another one, even if the results given this way 
are not in the truest sense quantitative. True outlier 
results are only given by the TGA and EDX results, 
and only in one instance each. Future studies can 
therefore likely give good results by just one or two 
of the above complementing techniques, saving 
time, money and other resources.
Table 4: Summary of results by sample prepared as thin section.
Sample 
Name
Mortar Type Binder Type
Binder 
Hydraulicity
Aggregate 
Type
B:A 
Gravimetric
B:A
Volumetric
Macro-Porosity
Volumetric
Ško-101.1a Rough coat Air Lime
Weakly 
Hydraulic?
Mostly 
ceramic
N.D. 1:1 (.5) 16.2%
Ško-101.1b Arriccio Impure Air Lime Non-hydraulic
Crushed 
marble / 
river sand
N.D. 1:1 (.5) 9.3%
Ško-101.1c Intonaco Air Lime Non-hydraulic
Nearly pure 
lime
Nearly pure 
lime
Nearly pure 
lime
N.D.
Ško-101.2a Arriccio Impure Air Lime Non-hydraulic Mixed N.D. 2:3 (.4) 10.8%
Ško-101.2b Intonaco Air Lime Non-hydraulic
Crushed 
Marble
N.D. 2:1 (.67) 5.7%
Ško-217 Cocciopesto Lime + Ceramic
Feebly 
Hydraulic
Mostly 
ceramic
.42 2:3 (.4) 2.4%
Ško-219
Drainage 
Render 
(Exterior)
Air Lime Non-hydraulic
Silicate + 
Carbonate 
Sand
.36 3:5 (.375) 14.8%
Ško-224
Masonry 
mortar
Air Lime Non-hydraulic
Silicate + 
Carbonate 
Sand
N.D. 3:5 (.375) 10.2%
Ško-239 Cocciopesto Lime + Ceramic
Moderately 
Hydraulic
Mostly 
ceramic
.43 2:3 (.4) 1.8%
Ško-250 Waterproofing Lime + Ceramic
Moderately 
Hydraulic
Ceramic and 
relic clasts
.80 3:2 (.6) 5.7%
Ško-303 Wall Render Air Lime Non-hydraulic
Silicate + 
Carbonate 
Sand
.44 2:1 (.67) 2.2%
Ško-310
Masonry 
mortar
Lime + Ceramic
Moderately 
Hydraulic
Mostly 
ceramic
.55 N.D. N.D.
Ško-315
Masonry 
mortar
Air Lime Non-hydraulic
Silicate + 
Carbonate 
Sand
N.D. 1:1 (.5) 5.1%
Ško-316 Waterproofing Lime + Ceramic
Mod. – highly 
Hydraulic
Mostly 
ceramic
.52 2:1 (.67) 7.1%
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CONCLUSIONS
This case study provided the opportunity to prove the 
efficacy of a novel method of determining the hydraulic-
ity index of a mortar by FTIR-i on polished thin sections. 
This method is invasive, but non-destructive (of the sam-
ple) and therefore could be used in cases when there is 
not enough sample material (or the resources) to make 
both a thin section and perform chemical or thermal dis-
solution. All 4 techniques (FTIR-i, SEM-EDX, TGA-DSC 
and chemical dissolution) are good for determining the 
hydraulicity index, i.e. pozzolanicity of a mortar. The 
techniques of TGA and chemical dissolution are de-
structive. SEM-EDX is not, but it is both more expensive 
and less definitive than FTIR-i. SEM-EDX shows that the 
minerals associated with pozzolanicity are in the same 
location, while FTIR-i indicates the co-molecularity of 
the types of silica and carbonate (and sometimes hy-
droxide) associated with pozzolanicity (Brunello et al., 
2019; Baragona et al. 2019a; Baragona 2021).
In general, hydraulic mortars were given special at-
tention in research, as they are particularly helpful in 
determining or confirming the use of a structure. In the 
Roman era, these mortars were often used in areas of 
high humidity or in direct contact with water, such as 
flooring or the walls of baths or cisterns (Adam, 1994), 
but also productive areas, kitchens, courts and gardens 
or other areas exposed to the elements as porticoes and 
facades. 
In the case of Školarice, the material destined to be 
analysed as examples of hydraulic mortars of the site, 
was in the first step selected because of its function and 
Figure 13: Results of four different, complementary methods for determining the hydraulicity index of a pozzolanic 
mortar. Key: Green – FTIR-i, Dark Blue – Chemical Dissolution, Light Blue – TGA, Red – EDX oxide percentage.
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Anthony J. BARAGONA et al.: ARCHAEOMETRIC ANALYSIS OF MORTARS FROM THE ROMAN VILLA RUSTICA AT ŠKOLARICE (SLOVENIA), 499–522
context, secondly by optically observing the samples, 
which were recognized as potential hydraulic mortars 
for their pale pink colour, due to the presence of crushed 
brick or of greyish granules hypothetically identified as 
pozzolana. Here presented analyses show that only a 
part of them were actual hydraulic mortars. This shows 
that criteria frequently used by archaeologists on site to 
identify hydraulic mortars do not comply with reality, 
and hydraulicity has in fact always to be tested.
The Roman villa at Školarice provides an interesting 
case study of early Imperial Roman architecture, built 
over successive building campaigns with a high level of 
sophistication. A wide range of well-established and the 
above-mentioned novel analytical technique showed 
the skillful use of different mortar recipes for a wide 
variety of applications at this Roman villa, which was 
probably also a waystation with baths that was addition-
ally a center of agricultural production. 
As mentioned before, the villa is arranged on two 
terraces, with completely different functions, on the 
lower terrace an elegant thermal complex is arranged, 
the other one hosts a productive storage area. Analysis 
showed that mortars of both areas were prepared with 
similar attention and sophistication, also with regard to 
the hydraulicity of the mortars, what we would necessar-
ily expect, being one the typical ambience of hydraulic 
mortars and high-quality architecture and decoration (i. 
e. baths), the other a space of functional character only 
tangentially connected to “wet” production activities. 
In some cases, the analysis provided important hints 
for determining the specific purpose of a structure. 
This was the case of sample Ško-217, sampled from 
the mortar covering a low structure in room AA, which 
was tentatively identified either with a productive ar-
rangement or, alternatively, with a simple floor. The 
low hydraulicity index of the sample makes the latter 
option more plausible, especially when compared to the 
hydraulicity index of sample Ško-239, which pertains to 
a typical productive arrangement, the torcularium. 
Similarly, the moderate hydraulicity of sample Ško-
310 must be pointed out: the sample came from the wall 
of an earlier building predating the construction of our 
villa. Rare structural remains (as well as plaster frag-
ments and some small finds) of this earlier building were 
identified in the thermal area and the use of a hydraulic 
mortar in its walls could indicate, that also this earlier 
building had already a similar function.
In this sample, but also in other samples dating 
from the 1st phase onwards, marble (which is not lo-
cally available) was predominately used as lime source 
stone, whereas mortars with sand aggregate Ško-303 
and Ško-315 pertaining to phase 1 showed to have 
(probably local) sandy limestone as a source of raw 
material for lime production. The more selective use of 
marble in the 1st phase implies that the material was 
at this time (second quarter of the 1st century AD) hard 
to acquire, but was specially chosen for structural uses 
that also required waterproofing. The import of marble 
in the area of north-western Istria was in Roman times 
generally very rare, as architectural decoration and 
sepulchral monuments show here predominantly to be 
made of limestone from Aurisina / Nabrežina (north-
eastern Italy), and only singular marble elements are 
documented (Krašna, 2022, 44).
On the other hand, the indiscriminate use of marble 
as a source for lime production in phase 2B (dated to the 
2nd century AD) seems to show its wider accessibility. 
However, sample Ško-294 taken from the structures of 
the basin in room 3 of the thermal area renovated in 
phase 2B, stands here out as it shows both marble and 
limestone as lime source stones. This would indicate 
that also in phase 2B, limestone was still used for this 
purpose, but was detected more rarely because there are 
fewer samples representing this building phase. 
Also the sand-lime mortar Ško-224, the only sample 
pertaining to phase 3 (3rd century AD), includes marble 
relics, as well as ceramic material, but is at the same 
time non-hydraulic, showing that marble was used as 
a lime source from the very first building of the site, 
predating the construction of our villa, throughout the 
1st and 2nd building phases and also until the 3rd one, 
and this seems to represent a very characteristic feature 
of this site.
Crushed marble is also used in the intonaco layers 
of the wall painting fragments (samples Ško-101.1 and 
Ško-101.2) and they match the marble used as lime 
source optically/structurally and chemically. A weather-
ing rim on a piece of marble used in the intonaco for 
Ško-101.1 indicates that the marble used for both this 
layer and the lime source for many of the samples was 
likely recycled. This implies that disused marble mate-
rial was imported for this use, or it was recycled from an 
adjacent earlier structure. The latter option is still more 
interesting, considered the older building predating the 
construction of the villa mentioned before.
At the same time, marble slabs and some other mar-
ble features were used especially in the thermal area of 
our site from the 1st building phase onwards. As they 
were not sampled for this analysis, we cannot confirm, 
if they also pertain to the same marble quality. But, 
in the area of north-western Istria the site of Školarice 
seems to represent an area of special concentration of 
marble materials, some of which used as raw material 
for lime production and as an aggregate in mortars, 
some as slabs and cornices (Žerjal & Novšak, 2020, 
77, 231–232, 578); parts of a statue of Dionysus dating 
to the first half of middle of the 2nd century AD were 
used in the wall of room SK4, created in the area of the 
large storehouse during the 4th building phase (this is 
during the second half of the 3rd century AD) (Žerjal & 
Novšak, 2020, 134, 204, 632, 633). This concentration 
of marble materials at this site could as well support 
the above-mentioned theory that the villa also func-
tioned as a mansio (“Aquae Risani”) on the route of the 
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main public road Via Flavia, being in this way better 
connected to the partially centralized logistics of the 
marble trade.
The intonaci of the wall painting fragments lack any 
lumps indicating the use of lime putty. Two samples 
(Ško-219 and Ško-303, pertaining to the 1st phase) 
contain pieces of charcoal, which we can recognize 
as lime production fuel residue. In all other samples, 
the quicklime was apparently thoroughly sieved after 
production or a clean burning wood was used, or of 
course both (cf. on this Laycock et al., 2018). The wood 
species appears to be a softwood, or conifer. Research 
about paleo-vegetation is still very rare, but the presence 
of conifers in this area in Roman times could be indi-
cated by the analyses made by Metka Culiberg (1997, 
136–137), however to a quite limited extent. It would 
be also possible that the wood was not necessarily of 
strictly local provenance but was imported from other 
nearby areas. This could have been done for construc-
tion, with leftover pieces being used as fuel for lime 
production.
The lime was very likely produced locally and in 
fact the remains of a lime kiln were excavated near 
the villa, at Križišče. The lime kiln was located along 
the road leading from the main road Via Flavia to the 
villa. Individual limestone pieces, which are not from 
the immediate surroundings, were found in the filling 
of the kiln and were meant to be burnt to lime. Another 
filling layer contained burnt earth, charcoal, limestone, 
and lime remains. Roman pottery was found in the fill 
as well, but remains of charred wood found inside the 
firing chamber were radiocarbon dated between 650 
and 820 AD (Novšak et al., 2019, 81–82; Kutnar, 2022, 
28–31). Despite this, excavators of the site considered 
this dating apparently incorrect, as they concluded that 
the lime kiln was used for the construction of the Roman 
villa at Školarice (Žerjal & Novšak, 2020, 21), where 
also a round structure for mixing mortar from the 1st 
building phase was found in the upper courtyard (cf. 
Figure 4, round structure north of the productive area). 
Inside this structure, ample remains of lime could be 
documented (Žerjal & Novšak, 2020, 378). These lime 
remains, both from the lime kiln and from the structure 
for mixing mortar, were not sampled for this analysis, 
but will be subject of research in the near future. As 
mentioned previously, marble was found to be the main 
source stone for the lime at Školarice, so (containing the 
lime kiln remains of limestone) it is likely that the radio-
carbon dating is correct. Considering the location and 
Roman finds in it, it is also possible, that the lime kiln 
was established for the construction or later renovations 
of the Roman villa and then reused in post-Roman time.
Open questions that could provide more detail into 
the case of the Roman villa of Školarice and its building 
materials, involve the provenance of the marble and 
sandy limestone source stones used for lime produc-
tion, as well as the tuffaceous material used as paving 
mentioned above. Additionally, analysis of any organic 
material that has left traces in the stone or soils of the 
site, e.g. GC-MS on oils or tannins soaked into the 
rough stone mosaic of the torcularium could be used 
to conclusively determine the usage of the productive 
arrangement.
ACKNOWLEDGEMENTS
The authors would like to thank Farkas Pintér at the 
Austrian Federal Office for Monuments (Bundesdenk-
malamt) for the use of his SEM-EDX as a back-up and 
to corroborate the results of the device mentioned in 
this work. The authors are also thankful to Maša Sakara 
Sučević at the Regional Museum of Koper and to Matjaž 
Novšak from Arhej d. o. o. for allowing us to perform 
this research. Special thanks go to Tina Žerjal from Arhej 
d. o. o. for providing photographs and plans from the ex-
cavation and for several fruitful discussions. The authors 
acknowledge the financial support from the Slovenian 
Research Agency (research core funding No. P6-0247).
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ARHEOMETRIČNA ANALIZA MALT Z RIMSKE VILE RUSTIKE 
NA ŠKOLARICAH (SLOVENIJA)
Anthony J. BARAGONA
Univerza uporabnih umetnosti Dunaj, Inštitut za konservatorstvo, Salzgries 14/1, 1013 Dunaj, Avstrija 
e-mail: tonybaragona@gmail.com
Katharina ZANIER
Univerza v Ljubljani, Filozofska fakulteta, Oddelek za arheologijo, Zavetiška 5, 1000 Ljubljana, Slovenija
e-mail: katharina.zanier@ff.uni-lj.si
Dita FRANKOVÁ
Češka akademija znanosti, Inštitut za teoretično in uporabno mehaniko, Prosecká 809/76, Prague 9-Prosek, Republika Češka
e-mail: frankeova@itam.cas.cz
Marta ANGHELONE
Univerza uporabnih umetnosti Dunaj, Inštitut za konservatorstvo, Salzgries 14/1, 1013 Dunaj, Avstrija 
e-mail: marta.anghelone@uni-ak.ac.at
Johannes WEBER
Univerza uporabnih umetnosti Dunaj, Inštitut za konservatorstvo, Salzgries 14/1, 1013 Dunaj, Avstrija  
e-mail: johannes.weber@uni-ak.ac.at
POVZETEK
V prispevku so predstavljeni rezultati analize malt, uporabljenih pri gradnji rimske vile rustike na Školaricah 
v Sloveniji. Analiziranih je bilo 19 vzorcev iz različnih mirkolokacij in faz, še posebej dvanajst vzorcev, ki so bili 
pripravljeni kot polirani petrografski zbruski. Ti vzorci so bili zaporedoma analizirani z optično mikroskopijo 
(OM), skenirno elektronsko mikroskopijo skupaj z energijsko disperzivno rentgensko spektroskopijo (SEM-EDX) 
in infrardečo spektroskopijo s Fourierovo transformacijo (FTIR-i), kar je omogočilo celovito analizo širokega 
spektra značilnosti in, kar je pomembno, kako so med seboj povezane. Posebna pozornost je bila namenjena 
reaktivnosti agregata in viru veziva apna. Določitev indeksa hidravličnosti veziva malte je pomemben kriterij 
pri oceni historičnih malt. Določili smo ga za keramično-apnene malte najdišča, in sicer s štirimi različnimi 
metodami (ki smo jih tako lahko tudi primerjali glede na dosežene rezultate): kemičnimi analizami z raztaplja-
njem vzorca, termogravimetrično analizo – diferenčno dinamično kalorimetrijo (TGA-DSC) ter analizo površine 
veziva z EDX in FTIR-i na ustreznih zbruskih. Pri slednji so bili spektralni podatki analizirani z analizo digitalne 
slike, ki je dala kvantitativne volumetrične rezultate, kar predstavlja novo tehniko za določanje hidravličnosti 
veziva za malto. S slikovnimi tehnikami smo določili tudi razmerje med vezivom in agregatom in poroznost. 
Rezultati so pomembno prispevali k interpretaciji vile, zlasti v zvezi z obsegom uporabe keramičnih frakcij kot 
pucolanskega ali hidroizolacijskega materiala.
Ključne besede: Rimska vila, Školarice, historična malta, FTIR spektroskopija, hidravlični indeks
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