Respecting the colours used by the artists who painted on ivory, we have ample details, as many of them have left behind speci mens of their colours and information concerning their technique and media.
Painting in oil upon copper, or very occasionally upon silver plates was an art that was peculiarly characteristic of the Nether lands and also of Italy. There was a long series of artists about whose art history we know very little, who in Holland produced numberless miniature paintings of this kind. They are seldom signed. The English and French miniature painters produced very few oil paintings on metal, in fact, hardly a single example can be attributed to any of them with certainty. In Italy, the art was more usually accepted, and there are several painters, particularly of the later Bolognese school, who are known to have practised this art, but small oil portraits on copper attributed to the great masters, such as Tintoretto in Italy, and Velasquez and El Greco in Spain, must be considered as having names attributed to them very much at haphazard. We have no evidence to support such a contention, but a considerable amount of evidence to set against it. There is a bare possibility that some of them may have ex perimented in such a medium, but they have left no record of such experiments, either amongst their papers or in contemporary records or by means of their own signatures.