Bulletin 2 (I:2), December 1963

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From the Laboratory of the National Gallery

by Nathan Stolow,
Chief Conservation and Scientific Research Division

Pages 1 | 2 | 3 | 4 | 5

Other Investigations

Scientific investigations may be carried out in the context of conservation treatment, as in the cases of The Toilet of Venus, and Le Pont de Narni, as described earlier, or they may be motivated by deterioration problems of another kind. On the other hand, analyses may be required in questions of authenticity.

In conclusion a few examples reflecting the application of laboratory investigation in these fields are given:

Investigation of Mould:

A number of paintings when returned to Canada from Sao Paulo Biennale of 1960 were found to be encrusted on the surface with mould. Laboratory investigation confirmed the existence of fungus which was disfiguring the paint surface (see Fig. 19).

"The material removed from the paintings is the mycelium and fruiting bodies of a fungus. The coenocytic hyphae of the mycelium, black spores, and spherical sporangium terminal on the long sporangiophore, suggest Rhizopus nigricans or Mucor mucedo. A few of the hyphae are septate - this may indicate a mixed culture, the septate mycelium probably belonging to Aspergillus niger." (25)

The optimum growing conditions for such fungi are 15 to 30 degrees centigrade with the relative humidity in the range of 95 to 100%. Growth can occur, however, in an environment with relative humidity as low as 70% . In general it is possible to remove the mould growth from the surface of a painting by mechanical means, usually combined with fungicidal washes. The efficiency of removal would depend on a number of factors such as the topography of the paint film, the chemical nature of the paint film and its continuity, the remanent action of the fungicide, and the chemical reactivity of the residual fungicide with the paint film itself. (26)

It is now standard practice in the National Gallery to apply fungicide to backs of paintings prior to shipment to countries where conditions conducive to fungus growth might exist. At the same time the entire packing case is disinfected using the same fungicide as has been used on the painting. Further precautions are taken by installing humidity and temperature buffers within the packing case to minimize tendencies for humidities to build up. (27)

Identification of Wood in "Viking" Sculpture:

In the latter part of 1960 there was the occasion to examine a sculptured head in wood which was dredged out of the Gaspé area (Percé), and thought by some to be of Viking origin. (28) The head, 10 1/4 inches high, and polychromed, is shown in Fig. 20. Examination of the wood by a standard method of thin sectioning and staining, followed by microscopic observation showed that it was Pinus Strobus L. or Eastern Canadian White Pine, rather than a wood of Scandinavian origin. Examination of moss-like residues on the base of the sculpture were identified as fresh water micro-organisms, and confirmed that the sculptured head came from a fresh water environment. There was no evidence to show that it had been immersed for hundreds of years in sea water. (29) The cross-sections of wood are illustrated in Fig. 21, and the fresh water algae in Fig. 22. It can now be assumed that the sculptured head is probably no more than 150 years old, and is of eastern Canadian origin.

Solvent Action Studies:

Previous fundamental studies on the action of solvents on aged linseed oil films have been continued. (30, 31) The information gained from such research is of value in understanding more completely the mechanism of action of solvent on varnish and on paint during the cleaning of pictures. By attempting to identify the nature of the leached materials from paint films it is possible to determine more precisely the reactivity of linseed oil films to solvents. The methods of micro-chemistry, infra-red spectroscopy, and gas chromatography are proving most useful in this regard. Essentially interest is being focused on the fatty acids, esters, and breakdown products which are extractable from aged paint, and which lend themselves to positive identification.

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