Catholic Church of the Sacred Heart, Edinburgh
A.M.D.G.

Technical Report For: Clare Meredith Brief: to make a technical examination of the materials of the painting. Examination procedure: Microscopic samples were taken from the painting, when temporarily in storage whilst in transit to be lined. These samples were taken in order to identify materials used and the structure of the paint. Samples were set both as cross sections and dispersions: cross-sections were viewed at x500 and in ultraviolet light; and dispersions were analysed by polarising light microscopy. Explanatory note: the various photographs that follow in this electronic version of the original report were achieved by scanning and then conversion to a format that would allow of reasonably quick downloading. Consequently, some of the detail will have been lost and there is no guarantee that the colour on the screen will match the colour in the original photographs.

REPORT

The preparation layers

The ground directly over the canvas was found to be a thick, chalk ground, containing natural coccoliths, and with a yellowish line at its upper edge. When viewed in ultraviolet light, this line could be seen to be slightly lighter implying that the chalk had been given a glue or resin coating after application to ensure that it was impermeable to the paint laid over it. Staining suggested that this ground was in a glue medium or had a very low oil content.

The chalk ground was laid on thickly in order to provide an absolutely smooth surface for the painter to work on. The way in which the chalk fills the interstices of the canvas weave can be seen in cross-section 1 [D606] from the tacking edge.

Cross-section 1[D606] of the tacking edge at the top of the canvas where it just turns over from the paint: photographed in reflected light x200

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Paint

The colours are laid on simply in only one or two layers. There was only one instance of a modifcation of the colour found in the samples, which was in the lighter part of the cloak of Christ.

The painter has used modern colours as well as traditional. For the vivid blue of the central figure he mixed Prussian blue with a recently produced blue, called Cerulean. Cerulean blue is cobaltous stannate, and was commercially available in England in the 1860s, and may have been available a little earlier in Germany. It was greenish blue colour and has been found used by Holman Hunt and other Pre-Raphaelite painters, as well as by Manet although not very popular with other artists since it has a rather chalky appearance in oil. However, Rauth may have been interested in this fresco-like effect of the blue. It can be seen in cross-section in the sample of the cloak of the central figure where it was still covered in varnish.

Cross-section 5(D610) of blue robe, central figure, where it had not been cleaned.
Reflected light x400

Cross-section 5(D610) of blue robe, central figure, where it had not been cleaned.
Reflected light x1000 and dispersions of same blue photographed at x1000 in plane polarised and crossed light (part reflected) showing blues, together with red and yellow earths, and lead white

There was another blue in the painting as well as Prussian blue and cerulean. In the pale violet colour of Christ's robe, French ultramarine is mixed in with lead white and a little crimson lake. French ultramarine provided a much purer blue, which contrasts well with the greenish colours around him, and allows his inner cloak to show well.

Cross-section 7 (D612) from pale violet of Christ's cloak
Photographed in reflected light at x100, x200, x400 and x1000.
Showinng two layers of paint over the ground, the first being a mixture of French ultramarine, crimson lake and traces of vermilion. The second and top layer being predominantly white with a little crimson lake, forming a pale highlight on the cloak.

Cross-section 7 (D612) from pale violet of Christ's cloak
Photographed at x400 and x1000

The red of the outer cloak of Christ was identified as vermilion. This scarlet pigment has been used since Medieval times, but this was the fine particled type known as wet-process vermilion, a 19th century product. This strong red can be seen in cross- section of a sample from the red of the outer cloak of Christ.

Cross-section 8 D613 of outer cloak of Christ
Photographed in reflected light at x400 and x1000 below

Dispersion of natural chalk from lower ground x400 crossed polars

Dispersion of chalk & lead white from lower & upper grounds x400 crossed polars

Dispersion of vermilion and a little lead white from red of Christ's outer robe
Photographed at x1000 in plane polarised light.

The flesh paint was found to be a mixture of crimson lake and vermilion in lead white, and with some yellow ochre mixed in. This is a traditional mixture for achieving the appearance of flesh, but it probably has more red and yellow than that of Christ's flesh to differentiate between the workman and the Saviour.

Cross-section of flesh paint of arm of man holding cross and Christ's sleeve
on the left.
Photographed in reflected light x200 and x1000 below

There are earth colours in use throughout the painting. Most obviously these can be seen in the pale brown of the areas depicting ground in the foreground. A cross- section of this area, at the extreme lower edge, showed that the artist had laid on a thin coat of paint containing red and yellow ochres in a lead white matrix. There are occasional particles of crimson lake in the mixture also.

Cross-section 9 D616 of buff ground at the lower edge
Photographed in reflected light at xl000

Christ's halo, on which thick layers of pale paint had been laid, presented a rather puzzling structure in cross-section, in that there appeared to be brownish red paint underneath the pale yellow underpaint. This may, however, be part of a drawing layer, since it lies over the second ground.

Drawing with a warm red paint was common practice amongst painters trained in traditional academy techniques, Since the layer is rather broken in appearance it is possible that this is a tiny fragment of a drawing out of the edge of the halo. (The sample was very near to the edge of the halo). The thickness of the halo was built up with the same underlayer of pale yellow, and what appears to be a yellow mordant over it, as can be seen in the main areas of gilding in the background.

Cross-section 12 (D617) of thick, pale yellow paint of Christ's halo.
Photographed in reflected at x200 (showing possible 'underdrawing')
and at x1000 below showing the upper layers of pale yellow, and a thin more intense yellow over.

Left hand edge of sample above

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Gilding

The gilding, sampled in the background was gold leaf laid onto a mordant of intense yellow. The brightness of this yellow, which appears to contain only a little yellow pigment, is probably enhanced by its translucency over a white preparation layer. It may have been made with a lake, although no base could be detected. The translucency may also come from extra oil being added to it as a mordant for the gold. There was no sign of a glue or other medium for the mordant when the samples were examined in ultra-violet light.

Much of the gilding is worn, and the yellow mordant has been exposed. This can be seen even on the small scale of the samples set as cross-sections.

Cross-section 2 (D607) of gilded background at upper edge
Reflected light, photographed at x200 and x1000 below

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Varnish

Several of the samples from the painting came from areas which had been left uncleaned, and showed multiple coatings from various varnishings in the past. Not all of these could be identified, and where some were more or less translucent, others were discoloured or yellowed, or had become infiltrated or covered with dirt.

The varnish over the gilding had at least two layers of what appeared to be a largely resinous substance. It had dirt over it in some places.

Cross-section 3 D608 from gilding where it was uncleaned. [some of the upper lavers of varnish may have cleaved away from the sample when handling]
Reflected light at x200 showing dirt at the upper edge

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