National Gallery Technical Bulletin Volume 11, 1987

Analyses of Paint Media

John Mills and Raymond White

This article continues our series summarizing the results of analyses of the media of National Gallery paintings. Both gas-chromatography alone and combined gas-chromatography-mass-spectrometry (note 1) have been used to obtain them, but we now more and more tend to use just the latter method since it is more sensitive and provides the added benefit of sure identification of minor components. The peak areas (used for calculation of the P/S ratios) with this method are obtained by summing the ion counts for the scans making up the particular peaks, and so could conceivably be different from areas of peaks yielded by the hydrogen flame detector used for gas-chromatography alone. Comparative tests, however, show the results to be comparable and unlikely to lead to significant error.

The standard chromatography conditions used now for all samples are: 25 m wide-bore (0.52 mm) quartz capillary column with methyl silicone-equivalent bonded phase; on-column injection; helium carrier gas at 37 cm/sec. linear velocity; temperature programming from 130 to 290°C at a rate of 5°C/min.

Artist	Picture	Date	Sample	Medium	P/S	Oil type	Note	
Bordon	Daphnis and Chloe No.637	c.1540(?)	1. Flesh, Chloe's knee
2. Red robe
3. Blue, Daphnis's garment
4. Blue, Chloe's dress
5. Green, top left	Oil
Oil
Oil
Oil
Oil + resin	2.1 2.0 2.3 2.2 2.8	?
?
Walnut?
Walnut?
Walnut	1	
Carlo Crivelli	Virgin and Child with SS.Jerome and Sebastian
No.724	After 1490	1. Red robe
2. Brown glaze on flower pot
3. White marble, L.H. edge
4. Green book
5. Brown marbling, R.H. edge
6. Virgin's blue robe, upper layer
7. Green marbling on predella frame	Egg. Some oil?
Egg
Egg
Egg. Some oil Egg
Egg. Some oil?

Egg + wax			2	
Carlo Crivelli	The Immaculate Conception
No.906	1492	1. White scroll
2. White architecture
3. Blue of Virgin's robe
4. Red of Virgin's dress
5. Brown glaze on marble
6. Green inside mantle	Egg
Egg
Egg
Egg
Egg
Egg			3	
Palma Vecchio	Portrait of a Poet No.636	c.1515–16	1. Grey ground
2. Red robe
3. Green leaf
4. White shirt	Oil
Oil
Oil
Oil	2.8
2.3
2.1
2.7	Walnut Walnut
?
Walnut	4	
Solari	A Man with a Pink No.923	before 1495(?)	1. Pale blue sky

2. Red robe, lower R.H. side	Oil + egg + resin
Oil + egg + resin	2.5

2.4	? ?	5	
Tura	An Allegorical Figure No.3070	c.1460	1. Green of inside robe

2. Red glaze on robe

3. White band at bottom
4. Dark blue sky

5. Red underlayer of robe
6. Pale green underlayer, base of throne
7. Green underpaint of dress
8. Green underpaint of green of masonry	Oil + some resin
Oil + some resin
Oil
Oil + trace
resin
Egg
Egg

Egg
Egg	1.4

1.4

2.52.0	Linseed

Linseed

Walnut Mixture?	6	
Tura	The Virgin and Child Enthroned
No.772	1470s(?)	1. Green pilaster, R.H. edge
2. Red glaze of pilaster, L.H. edge
3. Pink underlayer of sample 2
4. Brown capital, L.H. side	Oil
Oil + some resin
Egg
Egg	3.2
3.1	Walnut Walnut	7	
Zoppo	Pieta No.590	3rd quarter 15th C.	1. Light grey of sepulchure	Egg			8	
Ascribed to Campin	A Man No.653a

A Woman No.653b	2nd quarter 15th C.(?)	1. Blue of robe, L.H. edge

2. Red paint on reverse

1. Purple of robe, bottom L.H. edge	Oil + egg + resin
Oil + egg + resin
Egg + oil trace resin	1.5 1.4	Linseed Linseed	9	
Hoogstraten	A Peepshow No.3832	3rd quarter 17th C.	Numerous samples	Oil and egg			10	
Greuze	Portrait of a Man No.6500	1763(?)	1. Mixed colours, bottom edge
2. Mixed colours, R.H. edge
3. White ground	Oil
Oil
Oil	3.0
3.6
4.0	Mixture?
Mixture?
Poppy	11	
Købke	Northern Drawbridge to the Citadel in Copenhagen
No.6507	1837	1. Blue sky
2. Black, lower edge of rushes	Oil
Oil	1.6
1.3	Linseed Linseed		
Gainsborough	Dr Ralph Schomberg No.684	c.1770	1. Green-blue bushes, L.H. edge
2. White impasto of stocking	Oil
Oil	1.8
3.6	Linseed Poppy?	12	
Reynolds	Lady Cockburn and her three Eldest Sons
No.2077	1773	1. White of child's sleeve
2. Red drape, upper L.H. side

3. Black shadow on preceding area
4. Orange-yellow drape
5. Grey-white of dress, bottom edge	Oil
Oil + resin

Oil + resin + bitumen
Oil + resin
Oil	3.5
2.3

1.8

1.8
1.9	Poppy?
Walnut or mixture
Linseed

Linseed Linseed	13	
Van Gogh	A Cornfield, with Cypresses
No.3861	1889	Several samples	Oil +			14	

Notes to the Table

1. The palmitate/stearate ratios for this painting fall in the overlap region for linseed and walnut oils and one cannot be sure which has been used here. All of the samples contained significant amounts of pine resin (by GLC–MS; presence of dehydro- and 7–oxo-dehydroabietic acids), a considerable amount in the case of the green which was presumably of the 'copper resinate' type. As usual with the medium of copper greens, the oleate peak was strong (larger than the stearate).
2. Only samples 2 and 7 were also examined by GLC–MS. The former showed the presence of small amounts of pine resin; the latter of some beeswax (see (note 2)), but this seems unlikely to have been an original component. Egg is clearly the principal medium but one cannot be certain whether the apparent presence of small amounts of oil in three of the samples is original or due to later contamination; the presence of both media in two paintings by Crivelli, No.807 (note 3) and No.668 (note 4), has been noted earlier. Discussion of results on some further samples, taken from the predella frame in the course of its restoration, will be postponed until a future article on this topic.
3. In contrast to the preceding, results for this painting did not suggest the presence of any oil. Only one sample (the green, sample 6) was examined by GLC–MS. It showed no trace of resin components.
4. Only insignificant traces of resin were shown (by GLC alone) even in the green sample.
5. A distinctly low azelate peak in both samples suggested the probable presence of egg fats in addition to drying oil. This makes identification of the oil less certain but it was probably walnut. Amounts of resin were small.
6. Samples 1 and 2 showed a fair amount of pine resin and since both were semi-transparent glazes it seems likely that an oil-resin varnish medium was used in each case. We have discussed elsewhere (note 1) the possibility of distinguishing heat bodied oils (as would be formed in the preparation of oil-resin varnish by traditional methods) and raw oils. This involves the ratio of the C9 to C8 dicarboxylic acid esters, higher proportions of the C8 ester being formed on drying from the bodied oils. Higher proportions of C8 ester were indeed present in samples 1 and 2, C9/C8 being roughly 3.5 for sample 1 (green) and 2.6 for sample 2 (red) as compared with 5.6 for each of the straight oil samples 3 and 4, but it must be noted that these are apparently walnut oil, whereas the work cited above was on linseed oil. A similar possibility of the use of bodied oils has been discussed in connection with an Altdorfer painting (No.6463) (note 5). No.3070 is discussed at length on p.5ff.
7. A fortunate opportunity arose for taking a few samples from the edge of this painting by Tura for comparison with the preceding one. The results were gratifyingly clear-cut and, as can be seen, indicated a similar use of both egg tempera and oil media. The red and green glazes are used very thickly in some areas of the painting to render embossed details, and it can be seen in these that the paint has tended to sag towards its lower edge and must have been rather fluid. These thick details were in too good condition to allow sampling, but samples 1 and 2 appear to be the same paint used more thinly. The oil is clearly walnut and the proportion of resin is low; essentially absent in the case of the green. The C9/C8 ratios were high (about 6.0 and nearly 10, respectively) which would indicate that it was not a boiled oil varnish but, as was said above, we have not experimented on heat bodied walnut oil and are not sure of its behaviour.
8. Only one sample could be taken from this very small, thinly painted picture.
9. These two small panel paintings were in such good condition that sampling could be justified only in one or two places along the sides where paint had gone over the slightly raised lip of the ground at the edge. Azelate peaks were about half the size of palmitate for the first two, indicating dilution with saturated egg fats, while the single sample from No.653b was clearly largely in egg medium with just a little oil present. Despite the presence of egg, the P/S ratios for the first two samples are sufficiently low for one to be sure that the oil was linseed. Pine resin was present in all the samples, especially the first two. Unfortunately for lack of further samples the significance of these results cannot be certainly elucidated: that is, whether they represent the use of a different medium in different layers, or a mixed medium. On the basis of staining of cross-sections for protein, the presence of emulsion media, as well as the individual use of tempera and oil, have been reported in Early Netherlandish paintings (note 6, 7).
10. The complicated results from this painting are discussed on p.85.
11. Apart from the white it proved impossible to take samples of single-pigment paint. Clearly poppy oil has been used for the white but the lower P/S ratios of the other two samples could result from admixture of either walnut or a smaller amount of linseed oil.
12. The white seems most probably to be prepared in poppy oil but a ratio of 3.6 may also be just within the range given by walnut oil. Repeated sampling would be needed for certainty. This painting will be the subject of an article in a future issue of the ‘Technical Bulletin’.
13. Again, the white is most probably in poppyseed oil but may just be walnut. Presence of bitumen in sample 3 indicated by detection of hopanoid triterpanes with base peak at mass 191 (note 8, 9).
14. The results for this painting by Van Gogh are discussed at length on p.59.

References

1. Mills, J.S. and White, R., 'Organic Mass-Spectrometry of Art Materials: Work in Progress', ‘National Gallery Technical Bulletin’, 6 (1982), pp.1–18.
2. Mills, J.S. and White, R., 'The Mediums used by George Stubbs: Some Further Studies', ‘National Gallery Technical Bulletin’, 9 (1985), pp.60–64.
3. Mills, J. S. and White, R., 'The gas-chromatographic examination of paint media. Some examples of medium identification in paintings by fatty acid analysis', in N.Brommelle and P.Smith (eds.), ‘Conservation and Restoration of Pictorial Art’, Butterworths (London 1976), pp.88–92.
4. Mills, J.S. and White, R., 'Organic Analysis in the Arts: Some Further Paint Medium Analyses', ‘National Gallery Technical Bulletin, 2’ (1978), pp.71–6.
5. Mills, J. S. and White, R., 'Analyses of Paint Media', ‘National Gallery Technical Bulletin’, 7 (1983), pp.65–7.
6. Kockaert, L., 'Note sur les emulsions des primitifs flamandes', ‘Bulletin de l'Institut Royal du Patrimoine Artistique’, XIV (1973/4), pp.133–39.
7. Kockaert, L. and Verrier, M., 'Application des colorations a l'identification des liants de Van Eyck', ‘Bulletin de l'Institut Royal du Patrimoine Artistique’, XVII (1978/9), pp.122–27.
8. White, R., 'Brown and Black Organic Glazes, Pigments and Paints', ‘National Gallery Technical Bulletin’, 10 (1986), pp.58–71.
9. Mills, J.S. and White, R., ‘The Organic Chemistry of Museum Objects’, Butterworths (London 1987), Chapter 5 and pp.152–58.

National Gallery Publications Published by order of the Trustees

Scientific Adviser, John Mills
Chief Restorer, Martin Wyld
Editor: Ashok Roy

© The National Gallery 1987

All rights reserved. No part of this publication may be transmitted in any form or by any means, electronic or mechanical, including photocopy, recording, or any information storage and retrieval system, without the prior permission in writing from the publisher.

British Library Cataloguing in Publication Data

National Gallery

National Gallery technical bulletin.—Volume 11, 1987.
1. Painting — Conservation and restoration — Periodicals
I. Title
751.6'05 ND1640

ISSN 0140–7430
ISBN 0–947645–35–7

Designed by James Shurmer

Printed and bound in Great Britain by William Clowes Limited, Beccles and London