Characterization of the
binding medium used in
Roman encaustic paintings
on wall and wood.
This is an excerpt from a professional journal found on RSC
Publishing’s website, pubs.rsc.org. We are just presenting the
last two pages of this article written by Jorge Cunı, Pedro Cunı,
Brielle Eisen, Ruben Savizkyc and John Bove.
All About Encaustic
22
Winter
Experimental studies of wax paint
media.
Due to the small amount of organic compounds
and their degree of deterioration, the characterization
of the organic binding media in ancient
paintings is a difficult task that often shows unreliable
results. This is especially evident when
trying to carry out a replica of an ancient painting
by using the painting technique suggested at
the conclusion of the chemical studies. It is not
uncommon to observe that the physical characteristics
of the original painting cannot be reproduced.
In order to determine the capability of the
beeswax-and-soap painting technique identified
in this study to reproduce the characteristics of the
ancient encaustic paintings, replicas of Roman wall
paintings and Roman-Egyptian mummy portraits
were executed with wax and- soap encaustic paint.
Wax-and-soap wall paintings allowed the reproduction
of complex large-scale murals without the
need for giornate joints, as the painting was carried
out on dry lime mortar, a feature consistent with the
generalized absence of this type of joint in Roman
wall paintings. Paint was easily applied, allowing
the artist to reproduce both transparent and thick
brush strokes present in the original paintings.
Unlike the fresco technique, wax-and-soap paint
was able to reproduce the high color intensity of the
Roman paintings. Pigments that degrade with lime
– such as white and red lead, azurite, malachite,
orpiment and red lake – were used without
problems, calcium carbonate whites could be used
as white pigment and impastos showed a smooth
and greasy surface similar to Roman originals.
Besides, the soap content in the medium allowed
the artist to reproduce the crater formations occasionally
seen in Roman thick brush strokes Table 5
Identification of key components of beeswax and
linseed oil potassium soap. Carboxylic acids were
detected as methyl esters of the compounds listed
Peak label Compound identification Retention time/
min Mass detected (m/z) Relative counta
1 Henicosane 7.750 269.6 0.19
2 Hexadecanoic acid 7.752 270.1 0.23
3 9,15-Octadecadienoic acid 9.612 294.0 0.53
4 9,12,15-Octadecatrienoic acid 9.654 292.2 0.67
5 6,11-Eicosadienoic acid 9.711 297.0 1
6 9,12-Octadecadienoic acid 10.247 294.0 0.03
7 9,15-Octadecadienoic acid 10.446 294.0 0.04
8 Tricosane 12.065 324.6 0.14
9 Pentacosane 14.690 352.6 0.47
10 Heptacosane 15.966 380.3 1
11 Tetracosanoic acid 16.152 382.1 0.72
12 Nonacosane 17.732 408.7 0.81
13 Hexacosanoic acid 17.901 410.2 0.40
14 Hentriacontane 19.367 436.8 0.80
15 Octacosanoic acid 19.549 438.2 0.37
16 Tritriacontane 20.705 464.9 0.72
17 Triacontanoic acid 20.901 466.3 0.22
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The relative counts were determined by dividing
the ion current for a given peak by the ion current
for the largest peak in that spectrum. Fig. 4 Crater
formations in the paint surface of a Roman wall
painting from Villa dei Vetti, Pompeii, 62–69 AD (a),
mummy portrait of a youth with a surgical cut in
one eye, Egypt, 190–210 AD, encaustic on wood,
The Metropolitan Museum of Art, New York (b), and
wax-and soap encaustic on wood by Jose Cunı (c).
Craters are often found in wax-and-soap encaustics
due to the soap content in the binding medium.
This journal is The Royal Society of Chemistry 2012
Anal. Methods Downloaded by Columbia University on 21
February 2012 Published on 21 February 2012 on http://pubs.
rsc.org | doi:10.1039/C2AY05635F. Finally, wax-and-soap
wall paintings carried out during the last fifty years
in open porches and interior rooms showed high
durability and lack of decay. Beeswax-and-soap
paint applied at room temperature with a spatula
allowed the artist to reproduce the thick strokes
executed with a hard instrument shown in the
faces of many mummy portraits, and application
with a brush could accurately reproduce the long,
thin, transparent or thick brush strokes shown in
eyes, jewels and garments of these portraits. As in
Roman wall paintings, encaustic mummy portraits
show crater formations that are typical of wax-andsoap
paint due to its soap content. As mentioned
above, paint made of beeswax saponified with an
alkali does not allow the reproduction of neither
mummy portraits nor Roman wall paintings due to
its lack of cohesion.
Conclusion.
The eight binding media extracts of Roman
wall painting samples submitted showed strong
evidence of the presence of beeswax and fatty
acid soap through analysis by ATR FT-IR. Some
absorption bands present in these extracts were
not identified. In five of these samples the analysis
by GC-MS detected all of the hydrocarbons and
fatty acids determined from characterization of
beeswax, and also detected a significant amount
of unsaturated fatty acids, confirming the presence
of beeswax detected by ATR FT-IR and suggesting
that the paint medium also contained soap
that could have been produced with drying oil. The
results of testing the three remaining samples by
GC-MS were inconclusive due to the very small
size of the peaks, possibly caused by the low yield
of the binding medium obtained by the aqueous
extraction method used. The ATR FT-IR analysis