National Gallery Technical Bulletin September 1977

Analyses of Paint Media

John Mills and Raymond White

We present here in tabular form some of the results on analysis of paint media obtained by gas-chromatography from samples from National Gallery paintings. They are not all free from ambiguity, as might be expected from paintings which sometimes have a long history of reworkings and treatments of various kinds, neither has it been possible in all cases to follow up these doubtful results with testing by other means such as staining of cross-sections. They are nonetheless recorded here for possible future reference.

The analyses are based on determining the fatty acid composition of the paint sample after it has been saponified with alkali and the acids converted to their methyl esters. The method has been described in two papers (note 1, 2), and has also seen application in other laboratories besides our own, notably at the Louvre (note 3, 4). Put very briefly, the presence of a large amount of one component, azelaic acid, indicates the presence of drying oil while the presence of only a small proportion of this compound relative to significant amounts of other fatty acids such as palmitic and stearic acids indicates the presence of egg fats. The absence of significant quantities of these latter compounds implies the absence of both these media and hence (in the context of easel painting) of the presence of some other tempera medium such as glue. This can then be separately tested for.

The presence of both drying oil and egg-yolk in a sample results in a chromatogram with an intermediate level of azelaic acid. When such an intermediate level is found, therefore, the presence of both media is inferred. This is not very satisfactory evidence, though, and it is desirable to follow it up with other tests.

If the medium is thought to be oil then the ratios of the amounts of palmitic and stearic acids (the P/S ratios) are measured to give an indication of the probable identity of the oil-walnut, linseed, or poppy. It should be mentioned here that we now know that the P/S ratio for another possible oil, hempseed, falls within the same range as that of walnut and this introduces another element of uncertainty. However, this is an oil which has probably been only rather rarely used in painting as it tends to have a bright green colour when first expressed, but it is a possibility which must be born in mind. Obviously mixtures of oils will produce intermediate P/S ratios and we can therefore be most confident about our results when they lie at the two extremes of the range found, i.e. below 2.0 (linseed) and above about 4.0 (poppy).

Some of the paintings examined gave very consistent P/S ratios (e.g. Gossaert's ‘Adoration of the Kings’ and Titian's ‘Vendramin Family’) while others, even when they seemed to be in oil alone, gave very variable ones (‘Master of the Life of the Virgin’, Nos.252 and 253).

References

1. J. S. Mills, 'The Gas-Chromatographic Examination of Paint Media Part I. Fatty acid Composition and Identification of Dried Oil Films,' ‘Studies in Conservation’, 11 (1966), 92-106.
2. John S. Mills, and Raymond White, 'The Gas-Chromatographic Examination of Paint Media. Some Examples of Medium Identification in Painting by Fatty Acid Analysis,' ‘Conservation and Restoration of Pictorial Art’, (ed. N. Brommelle and P. Smith) Butterworths (1976), 72–77.
3. J.-P. Rioux, Note sur l'Analyse de quelques Enduits provenant de Peintures francaises des XVII et XVIII Siècles, Laboratoires de Recherche des Musées de France, ‘Annales’, 1973, 35-43.
4. S. Delbourgo and J.-P. Rioux, Contribution a l'Étude de la Matière picturale des Impressionistes, ibid, 1974, 34-42.

Artist	Picture	Date	Sample	Medium	P/S	Oil type	Note	
Giovanni Bellini	The Madonna of
the Meadow
NG 599	End of
15th C.	1. Unpigmented priming on ground
	Egg + trace
oil?
				
			2. Blue underpaint	Egg + oil?				
Giovanni Bellini	The Agony in the
Garden
NG 726	c. 1465	Blue paint of trees	Egg				
Cima da Conegliano	S. Sebastian
NG 4946

	End of
15th C.

	1. Grey background

	Oil

	1.55– 
1 .96
	Linseed

	1	
			2. White loincloth
	Oil
	1.67
	Linseed
		
	A Male Saint NG 4945	End of
15th C.	1. Grey background
	Oil	1.84	Linseed		
			2. Blue robe
	Oil
	1.65
	Linseed		
			3. Pale blue spandrel
	Oil
	1.61
	Linseed
		
			4. Red robe	Oil	1.51	Linseed		
Girolamo da Treviso	Madonna and Child
with SS. and Donor
NG 623	2nd quarter
16th C.	1. Saint's red robe, L.H.S.
	Oil

	1.6

	Linseed

	2	
			2. Grey base of pillar	Oil	2.16–
2.40	Walnut?		
Ascribed to
Fra Filippo Lippi	Virgin and Child.
NG 3424	15th C.	1. Brown scumble	Egg + oil?			3	
			2. Pink stripe, L.H.S.	Egg + oil?				
			3. Blue Virgin's robe,
top layer	Egg
				
			4. ditto, lower layer	Egg				
			5. White, Virgin's dress
	Egg + trace oil ?				
			6. Green, T.R.H. corner	Egg				
Andrea Mantegna	Introduction of
the Cult of
Cybele to Rome
NG 902	c. 1505	1. Red-brown, top	Glue			4 	
			2. Grey, R.H. edge	Glue				
			3. White stripe of pillar	Glue				
Melone	The walk to Emmaus
NG 753	1st quarter
16th. C.	1. Brown tree trunk Top L.H.S.	Oil
	2.6	Walnut
		
			2. Reddish paint, central figure	Oil	2.1	?		
Evangelista
Preda or
Associate of
Leonardo da Vinci	An angel in Red
with a Lute
NG 1662	End 15th C.	1. Dark grey overpaint L.H.S.	Oil	2.72	Walnut	5 	
			2. Lighter grey under 1
	Oil
	3.05
	Walnut		
			3. Grey-white of centre niche	Oil
	3.01
	Walnut
		
			4. Red of robe	Oil
	2.06	?		
			5. Dark grey of niche, top L.H.S.	Oil
	2.65
	Walnut
		
			6. Brown edge of wing, R.H.S.	Oil
	2.64 
	Walnut
		
			7. Red-brown under grey, R.H.S.	Oil	2.43	Walnut		
Sassetta	The Whim of
S. Francis to become
a Soldier.
NG 4757	2nd quarter
15th C.	1. White, R.H. column	Egg			6	
			2. Dark red glaze over silver	Egg
				
			3. Blue sky	Egg				
			4. Green chest	Egg				
Titian	Venus and Adonis
NG 34	Mid 16th C.	1. Brown on bow	Oil	1.52	Linseed		
			2. Adonis's leg	Oil	2.14	Linseed		
	The Vendramin
Family
NG 4452	Mid 16th C.	1. Deep red glaze central profile figure	Oil
	2.80	Walnut
		
			2. Blue sky	Oil
	2.40
	Walnut
		
			3. Boy's red stocking	Oil
	2.60
	Walnut
		
			4. Maroon robe, old man centre	Oil
	2.90
	Walnut
		
			5. Black boy's robe L.H.S.	Oil
	2.60
	Walnut
		
			6. Ermine sleeve, old man	Oil	2.50	Walnut		
Austrian School	Trinity with
Christ Crucified
NG 3662	15th C.	1. Red of front wing of angel	Egg			7	
			2. Red robe L.H. Angel	Egg
				
			3. Green dress of R.H. angel	Egg				
The Master of
Liesborn	The Presentation
in the Temple
NG 257	2nd half
15th C.	1. Brown-green glaze of tiles	Oil
	1.45
	Linseed
		
			2. Dark grey of arch top R.H.S.	Oil	1.8	Linseed		
Circle of the
Master of Liesborn	SS. Ambrose,
Exuperius and Jerome
NG 254	2nd half
15th C.	1. Red of S. Jerome's robe	Oil + egg

			2. Grey pillar	Oil	3.0	Walnut		
			3. Red of S. Ambrose's robe (red lake glaze)	Oil	1.76	Linseed		
Master of the Life
of the Virgin	SS. Jerome, Bernard,
Giles and Benedict.
NG 250	2nd half
15th C.

	1. Grey-white robe of Saint, R.H.S.	Oil
	3.4

	Walnut

	8	
			2. Black robe	Oil (+ egg?)
				
			3. Blue sky	Oil (+ egg?)				
	The Conversion of S. Hubert. NG 252
	2nd half
15th C.
	1. White of sleeve	Oil	1.93	Linseed		
			2. Brown horse	Oil	2.22	?		
			3. Green trees	Oil	3.23	Walnut?		
	The Mass of S. Hubert. NG 253	1485 – 1490	1. Green L.H. edge	Oil	4.02 	Poppy		
			2. White of altar cloth	Oil	4.48	Poppy		
			3. Red cloak, L.H. figure	Oil	3.0	?		
1.	
Master of the S. Bartholomew Altarpiece	Ss. Peter and Dorothy. NG 707	Late 15th early 16th C.	1. White of sky	Lean oil 			9	
			2. Green brocade	Lean oil				
Master of S. Giles	The Mass of S. Giles NG 4681	c. 1500	1. Green drape, L.H.S.	Oil + egg 			10	
			2. Blue robe of king	Oil + egg				
			3. White altar cloth	Oil + egg				
			4. Red of carpet	Oil + egg				
	S. Giles and the Hind. NG 1419	c. 1500	1. Grisaille on reverse, grey-white of S. Peter's head	Oil

	3.10

	Walnut

			2. Pale blue sky	Oil
	3.32 
	Walnut 		
			3. Green foliage, bottom edge	Oil
	3.33	Walnut		
			4. Red of cloak	Oil	3.38	Walnut		
Master of Delft	Scenes from the Passion. NG 2922	early 16th C.	1. Grisaille on reverse. Virgin's robe. L.H. wing	Oil (+ egg?)	(1.95)		11	
			2. Grisaille on reverse brown niche. L.H. wing	Oil (+ egg?)	(2.17)			
			3. White tail of horse L.H. wing	Oil (+ egg?)
	(2.10) 
			
			4. Green of sky, Top R.H. edge, R.H. wing	Oil (+ egg?)
	(2.00) 
			
			5. Grisaille of R.H. wing, niche	Oil (+ egg?)	(2.20)			
Gossaert	The Adoration of the Kings. NG 2790	1st quarter 16th C.	1. Angel's green robe	Oil	1.86 	Linseed 		
			2. Virgin's blue robe	Oil
	1.81 
	Linseed		
			3. Red of wing of upper L.H. angel	Oil
	1.85	Linseed		
			4. Grey-white of masonry	Oil
	1.81 
	Linseed		
			5. Blue grey of ditto	Oil	1.87	Linseed		
Carel Fabritius	Self Portrait NG 4042	1654	1. White cloud R.H.S.	Oil	1.60 	Linseed 		
			2. Blue of sky R.H.S.	Oil	1.45	Linseed		
Gerrit Heda 	Still Life 
NG 1469 
	1640s 	1. Black paint
	Oil	1.65 	Linseed 		
			2. White tablecloth
	Oil
	1.78	Linseed		
Rembrandt	Hendrickje Stoffels 
NG 6432	1659	3. Red background L.H. edge	Oil
	3.10	Walnut		
			4. White highlight of robe.	Oil	3.30	Walnut		
Van Dyke
(style of)	Two Englishmen NG 3605	17th C.	1. Brown velvet tunic
	Oil
	1.41
	Linseed 		
			2. Snuff-coloured drape
	Oil
	2.45
	Walnut		
			3. White highlight of satin	Oil	1.9	Linseed		
Reynolds	General Sir Banastre Tarleton 
NG 5958	18th C.	1. Red/brown of L.H. drape	Oil	1.75
		12	
			2. White of cloud	Oil	2.73			
			3. Beige of cloud edge	Oil	3.80			
			4. Brown rocks	Oil + resin 	1.86			
			5. White highlight	Oil + resin	2.5			

Notes to the Table

1	Two samples analysed.
2	Two samples analysed.
3	This painting seems to be predominantly in egg-tempera with the possible use of some oil in scumbles.
4	The fatty acid content of these samples was very low though somewhat higher in the first than the other two. Oil is definitely absent and the results are more in accord with glue-tempera than egg-tempera. The use of the latter in some of the thicker, more substantial paint is possible, however.
5	For a description of the possible extent of overpainting in this picture see The National Gallery, Jan 1973 – June 1975 (1975), 67.
6	See separate article in this Bulletin.
7	The three samples were very small but definitely showed the absence of oil. The fatty acid levels were very low, resulting most plausibly from lean egg-tempera.
8	The very varied results in these three paintings cannot be rationalised at present. The high P/S ratios of the Mass of S. Hubert seem strongly to suggest the use of poppy oil. The various lower figures for the other samples probably result from mixtures of oils.
9	Very small samples made measurement of the P/S ratios unreliable.
10	See pp. 49–56 this Bulletin.
11	The azelate peaks in all samples were somewhat lower than normal for oil alone, about 75% of the level of palmitate. The medium is therefore probably predominantly linseed oil with some egg but whether the latter is admixed or present in separate layers has not been determined as yet.
12	These very varied ratios perhaps reflect Reynolds's experimental approach to painting. Samples 3 and 4 were found to contain diterpenoid conifer resin components but the particular resin cannot be specified.

©1977, The National Gallery, London

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