The most accessible article I've found is by Hubert Baija from the Rijksmuseum. Here is an excerpt from an article about restoring a 17th century frame:
“An experiment with shell gold was quite successful, but it seemed wasteful to use up so much of it on such a large surface. Watercolors made with mica gold pigment combined with raw umber and black proved to be a good alternative (figs. 15–17).14 In the next stage, these gold-colored retouches were toned to a warmer, less greenish tint with alcohol-soluble walnut-colored wood stain in a solution of synthetic resin15 in ethanol. The resin also gives a degree of protection against handling of the objects for the water-soluble layers underneath.”
Reply With Quote