TABLE 2 Seurat’s tube paints and their binding media
1 Many of the samples examined contained mixtures of pigments. In some cases the palmitate/stearate ratios obtained were intermediate between those expected for linseed oil and those for poppy oil, so within the region for walnut oil. It would therefore be possible to interpret these results as suggesting the presence of walnut oil in the paint. However, examination of the pigment content suggested that these were better interpreted as mixtures of linseed and poppy: most contained lead white which was usually bound in poppy oil, while the other pigments, where a pure sample could be examined, usually contained linseed oil. It should also be remembered that Seurat could have added a little extra oil to his paint to adjust its working properties, which was not necessarily the same as that in the tube.
2 An indicator for the presence of soaps, probably of lead, in several samples, most notably from The Bridge at Courbevoie, is an apparent increase in the proportion of palmitate in the paint. Soap formation might be expected over time and might be encouraged by the presence of certain pigments or additives, or even water, but it seems unlikely that this would affect the oil fatty acid proportions so unevenly. The effect observed may be due to the deliberate addition of a palmitate soap at some stage during the manufacture or packing of the paint, possibly to improve wetting of the pigment by the oil medium. French ultramarine, for example, is a hydrophilic pigment and, without some effort or the assistance of a wetting agent, is poorly wetted by the oil. In one or two cases the raised palmitate content meant that the analytical results could not be interpreted.
3 Unfortunately the pigment content of these samples was not examined.
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