3 PAINT MEDIA AND SURFACE COATINGS

Some of Bierstadt's late paintings have varying types of surface texture that contrast to the smoother surfaces his paintings usually exhibit. This surface texture cannot be blamed on a graphite ground layer because it also occurs in paintings without graphite, for example in the Corcoran version of The Last of the Buffalo. The surface in this painting has a curiously granular appearance, and it is possible that Bierstadt may actually have textured the ground layer. The paint is somewhat powdery and seems to suffer from a lack of oil binding medium. There are pinpoint losses throughout the paint layer that appear to correspond to the tips of the textured ground and may be the result of mechanical action during previous cleanings. Other late paintings seem to have a thick, rich, slightly wrinkled texture in the paint layer. One possible explanation is that Bierstadt was experimenting with paints in this late period, at least sometimes with unfortunate results. He might even have tried some of the paints containing oil and water emulsions for which patents are common by the 1880s. Wolbers (1991b) gives an example of a typical recipe of the period that includes water, linseed oil, and, in lesser amounts, white spirit, caustic soda, copal, potato starch, casein, and manganese abietate.

Wolbers (1991a) found that the paint in both versions of The Last of the Buffalo stains positive for both oil and protein, indicating that casein or glue may have been present in the medium. It is possible that Bierstadt experimented with an emulsion paint in which the ingredients did not dry to form a satisfactory paint film, or in which a particular combination of ingredients caused deterioration. Explaining the myriad surface effects of some of these late paintings will require further research.

William MacLeod's entry for July 22, 1886, in the curator's journal of the Corcoran Gallery of Art (8:149) sheds some light on Bierstadt's use of surface coatings: “Mr. Bierstadt called.… He recommends going over his ‘Mt. Corcoran’ with ‘poppy oil’ & says the best varnish ever made is of copal dissolved in boiling turpentine. Weidenbach dissents from it.” Copal spirit varnishes made without oil were commercially available in England in the 19th century. In experiments with copal at the Canadian Conservation Institute, Carlyle (1998) has found that the spirit varnishes are similar in appearance to mastic and damar. Unlike these better-known resins, however, after a period of artificial light-aging the copal spirit varnishes continued to yellow significantly when placed in dark storage, but some reversal in yellowing did occur when they were again exposed to normal light conditions for only a few weeks. Moreover, removability of copal spirit varnishes has not been tested, and they may prove more intractable than mastic or damar films (Carlyle 1998). I have not found any evidence of copal varnish being used in the treatment of paintings in the Corcoran Gallery of Art. However, from the curator's journal and existing evidence it is clear that paintings were sometimes oiled.