Experiments with Oil-Paints

Amongst the series of trials of oil-paints made by the author of this handbook, one set first arranged in 1880 may be described here. Chance's colourless plate-glass was employed as the painting-ground, so as to avoid all interference with the pigments from the surface on which they were spread; glass presents the further advantage of permitting a complete examination of the back of each specimen, and of changes in its translucency, opacity, or texture. Each glass measured 8 inches by 6; the complete series was prepared in duplicate - one for preservation in darkness, the other for exposure to all the light that could be secured (in Kew) during live years in a window facing nearly south-west. The majority of the paints tried were obtained from four firms (Messrs. Winsor and Newton, Messrs. Roberson and Co., M. Edouard of Paris, and Schoenfeld of Düsseldorf). Specimens of each pigment were reserved for further examination and analysis. Some of the chief results obtained are given in the annexed table; a few remarks on the changes observed in some of the pigments which had been mixed with flake white are added:

A series of trials of seventeen madder colours in oil was carried out in 1893. These were all prepared by Lefranc of Paris. The samples were spread on thin lantern glass 4 in. x 4 in., and when dry each glass was cut in half. One half was exposed to sunshine from March 26 until October 26, the other half of each specimen being kept in darkness. At the end of the seven months the halves of each sample were rejoined and carefully mounted, and thus an instructive set of slides obtained. The results are given in the following table, in which I have grouped together those varieties of 'laque de garance' which resembled one another in their degree of stability:

In the fourth or least stable group, comprising the varieties of madder brown, it was noticeable that the yellow constituent of the colour was most affected by exposure, the brun foncé and the nuance bitume losing all their characteristic beauty of hue and becoming of a dull, poor, rusty tint and not retaining over 20 percent of their original depth. Even in Group II. the golden hue of the rose dorée was the only chromatic element of this madder paint which had been lost to an appreciable extent during the six months' exposure.

Experiments as to the degree of stability possessed by many other oil-paints have been made; the results will be found for the most part incorporated with the accounts given of the several pigments in Part III. One remark may perhaps be usefully introduced in this place with reference to the differences observable in the quality and behaviour of pigments bearing the same name but obtained from different artists' colourmen. It is a good plan to place side by side on three trial-plates several 'makes' of the same paint and to keep one set in darkness, and to expose a second set to sunshine and a third set to strong diffused daylight. It will sometimes be found that the fascinating colour-quality which at the first glance recommends one sample is not preserved after exposure, although the reverse experience is not uncommon. It must not be forgotten that although the composition and constituents of the vast majority of pigments, both natural and artificial, are known, yet there are differences in the methods of preparation which, in some cases at least, are kept secret, and which result not in differences of nuance only, but in differences of stability also.