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The wall paintings of the Chapel of the Holy Rood were
analysed in Chemical Laboratories of the National Gallery
in Prague in 1980 and 1982. The samples for analysis were
taken by Academic Painter Jan Pasálek. Here we shall summarize
only the main findings. The full text of the laboratory
reports, including a description of methods used,
is available for study in the Archives of Historical Art
Technology and in the National Gallery.
Sample No 1 – 24 Old Men, background
In the lowest position on the cross-section is a grey
siliceous layer 0.092mm thick. Microscopically it is identical
to the siliceous layers on the panel paintings of the
same period, e. g. the panels from Bubeček and the Alterpiece
from Zátoň. The histochemical test for binding media was
positive both for protein and for oil. The supplementary
solubility test showed the presence of glue with an admixture
of oil.
Above the siliceous layer lies an ochre base 0.025 mm
thick. The microrystal-line substance with particles less
than 0.001 mm in diameter contains colourless particles
as well as yellow and red ones. The ground layer is bound
with oil. The histochemical test for the presence of proteins
was negative. The layer of white colour 0.025 mm thick
consists of lead white with traces of ochres. The histochemical
test for binding media in the colour layer was positive
both for proteins and for oils. The supplementary tests
– the foam test, solubility in 10 % potassium hydroxide,
396 nitric acid, reaction with Mil-Ion 's reagant –
were carried out on a layer of paint also including
the ochre ground. In the evaluation of the results we
had to take this circumstance into consideration. We are
of the opinion that the binding agent in the colour layer
is egg tempera with the addition of oil.
Results of spectral analysis:
Ca Mg Pb Si Al Mn Cu Fe Ag (Sn)
Further samples taken from the same scene (the 24 Elders
of the Apocalypse) gave the following composition of colour
layers:
– blue cloak of the Elder in the middle of the front row:
ultramarine, azurite and lead white
– blue-green cloak of the Elder in the second row on the
left: azurite, lead white and a tiny amount of red
organic lake (under this layer is a very thin layer
of charcoal black)
yellow hair of the same figure:
In the microscopic fragments (grey siliceous layer, microcrystalline
ochre ground and thin yellow paint), which it was impossible
to separate, there were found yellow and red ochres, colourless
siliceous particles, lead white and charcoal black
– the Lamb – grey modelling in the highlights:
lead white, charcoal and a negligible admixture of
azurite
Sample No. 2 – the God of the Apocalypse – blue
background
The grey siliceous layer 0.185 mm thick and the ochre
base 0.016 mm thick are identical with the layers of sample
No. 1. Over the ochre base is a thin insulating layer
consisting of a thin aplication of oil. The painting
consists of two layers. The lower is light blue and contains
lead white, azurite and charcoal black. The tiny admixture
of red was considered under the microscope to be vermilion.
This layer is 0.066 mm thick. The upper layer, dark blue
in colour, is made of azurite crystals 0.010 to 0.017
mm in diameter. This layer is 0.140 mm thick.
The test for binding media in the paint was carried out
in the same way as for sample No. 1. The reactions were
again positive both for protein and for oil. Even though
the supplementary tests cannot differentiate the nature
of the proteins, we presume egg tempera with the addition
of oil.
The supplementary samples from the same picture gave us
the following determination of pigments:
– the red layer from the monochrome painting of the Angels
around God contains minium as the dominant pigment and
a small amount of ferrous red is also present.
– the blue layer from the same monochrome painting (the
»Blue Angels«) consists of azurite and ultramarine (lapis
lazuli) in proportions ofl:l. The layer also includes
lead white.
In another sample two colour layers can be seen under
the stereo-microscope. The upper layer lies on a blue-green
layer, the shade of which is created by a greater
amount of azurite, the robes of God: lead white and charcoal
black
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– the right hand of God: lead white, charcoal black,
admixture of yellow and red ochres and azurite
– brown background bottom right (powder sample):
Fragments prevail with a grey siliceous layer, ochre
base and traces of oil gilding. The brown tone is not
formed by brown pigment (only yellow and red ochres are
present), but by the general surface dirt. The oil gilding
on an ochre base was analysed on the sample from the Throne
of God:
Above the siliceous layer lies an ochre base 0.020 mm
thick. To this is applied a thin layer of oil 0.008
mm thick. On the oil base is a strip of gold 0.006
mm thick. This is oil gilding which was identified histochemically
and by solubility tests.
Pastiglia from the picture of Christ and Madgalene
The plastic ornament is on two layers. The lower layer
of ochre paint contains yellow and red ochres and lead
white. It is bound with oil. Over it is a grey-brown
layer recalling the grey siliceous layer of the panel
paintings from the Bohemian Gothic period. It contains
siliceous and lime particles with an admixture of yellow
and red ochres. The binding agent in this layer is starch,
the grains of which, 0.006 to 0.041 mm in diameter, were
identified as rye starch. On the basis of the solubility
tests we also presume the presence of glue.
Sample No. 3 – the Red Book (Christ, Mary, Martha)
Spectral analysis:
Ca Si Al Fe Hg Mg Pb (Ag) (Mn) (Cu) (Sn) Over the ochre
base, 0.020 mm thick, is a layer of lead white (0.107
mm). Over this again is a thin layer (0.016 mm) of
vermilion and lead white. The binding media in all the
layers are identical to those in sample No. 2. (Sample
No. 2/supplements from 1982) from the scene of Christ
with Mary and Martha, not published here (carnation of
Christ) brought the following findings:
The layer closest to the plaster is a siliceous layer
of light grey colour, 0.041 mm thick. It contains siliceous
parts of white, grey and black colour, pigmented with
yellow ochres The histochemical analysis was positive
both for the presence of oils and proteins. We presume
that the oil soaked through from the upper ochre layer,
which is strongly bound with oil. In the siliceous layer
the presence of starch was also indicated. Above the siliceous
layer there is an ochre layer 0.020mm thick, made up of
yellow and red ochres and lead white. The painting over
the ochre layer consists of two equally thick (0.024mm)
applications of lead white, of which the upper ispigmented
with vermilion, yellow ochre and charcoal black.)
Sample No. 4 – grey cloak (Christ, Mary, Martha)
Over the ochre ground (0.158 mm) there is grey panting
(0.044 mm) of lead white and charcoal black. The sample
applies to the binding media as given for the previous
samples.
Conclusion
From the point of view of painting technology the wall
painting is composed as follows: on a thick layer
of plaster lies grey siliceous layer, microscopically
identical to the silicious layers of the panel paintings,
e. g. the panels from Dubeček and the Altarpiece ofZátoň.
Over the siliceous layer there is thin ochre ground containing
yellow and red ochres with lead white. Through supplementary
analysis the presence of lead white in the ochre ground
was also shown in the scenes of the »24 Elders« and the
»God of the Apocalypse«. The coat of oil over the ochre
ground was evident only in sample No. 2. The painting
contains the pigments of the period-lead white, yelow
and red ochres, vermilion, ferrous, red, azurite, natural
ultramarine and charcoal black.
The analysis of the binding media, due to the very thin
layers, was mainly carried out microchemically with a compact
sample and to the partial results were confirmed histochemically
on the cross-sections. The siliceous layer is bound with
protein (glue) and a smaller amount of oil (not even
with fluorescent analysis is it possible to decide whether
this is not due to the soaking through of oil from the
ochre ground) The layer also contains rye starch, which
was subsequently identified also in the sample in previous
reports. The ochre ground is bound with oil. The painting
contains an emulsion bonding medium – protein with
a small amount of oil. The supplementary solubility
tests lead us to suppose egg tempera with the addition
of oil.
author
Jindřich Tomek,
Dorothea Pechová, AHVT I 010 (Q. D.)
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24 Elders background
1 white layer – lead white with traces of ochres
0,025 mm
2 ochre ground, 0,025 mm
1 0,092 mm grey siliceous layer
The God of the Apocalypse – blue background
6 thin layer of varnish or impurities, 0,021 mm
5 blue azurite and lead white, 0,140 mm
4 light blue azurite, lead white,vermilion, carbon
black, 0,066 mm
3 insulating interlayer,0,005 mm
2 ochre ground,0,016 mm
1 šedá křemičitá vrstva, 0,185 mm
Christ, Mary and Martha – red book
3 vermilion and lead white 0,016 mm
2 lead white, carbon black, 0,044 mm
1 ochre ground – yellow and red ochres, lead white, 0,020
mm
garment of the same picture
2 lead white, carbon black, 0,044 mm
1 ochre ground – yellow and red ochres, lead white, 0,058
mm
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