Note 291 — Chapter XIX · (XXXIII.)

The difference in colour between gold and silver will naturally affect the choice of the transparent vitreous pastes that are to cover them, and there are also considerations of a chemical kind which prevent the use of certain pastes on certain metal grounds. For example tin has the property of rendering transparent enamels opaque, and transparent pastes cannot be used over metal grounds wherein tin enters into the composition. Cellini, who gives the same caution as Vasari, takes as an illustration transparent ruby coloured enamel, which he says cannot be used over silver, for a reason which has about it a reminiscence of the ancient alchemy, namely, that it is a product of gold and must be employed only over its kindred metal! On the other hand he forbids for use with gold yellow, white, and turquoise blue. We are indebted for some special information on this highly technical subject to the kindness of Mr H. H. Cunynghame, C.B., who writes: ‘There are two distinct reasons why different enamels are used on silver and gold respectively. The first is an artistic reason. Transparent reds do not show well over silver, the rays reflected from a silver surface not being well calculated to show off the colours of the gold. In fact silver absorbs those rays on the transmission of which the beauty of gold-red largely depends, whence then it follows that transparent blues and greens should be used on silver, and reds, browns, and the brighter yellows on gold. In addition to this, silver has its surface disturbed by the silicic acid in the enamel. The consequence is that ordinary enamels put on a silver surface are stained. To prevent this it is desirable to add some ingredient that dissolves and renders colourless the stain. For this purpose therefore special fluxes or clear enamels are made for silver. They usually contain manganese and arsenic. The first of these has such a property of “clarifying” enamels and glazes that it used to be called the potter’s “soap,” for it cleaned the glazes on china. The other is also used for the same purpose.... As silver alloy is more easy to melt than gold alloy, fluxes, i.e. clear enamels for silver, are much more fusible than those for gold.’