“Fourth. The flux of purple is made with 3 parts of red lead or of litharge, 1 part of Etampes sand, and 5 parts of crystallized boracic acid.
“Fifth. The flux of violets is made of 27 parts of litharge or red lead, 2 parts of Etampes sand, and 11 parts of crystallized boracic acid.
“Sixth. The flux of greens employed, as well as the two preceding M. Salvetat, was prepared by him with 8 1-9 parts of red lead or litharge, 1 part of Etampes sand, and 2 parts of crystallized boracic acid.
“Seventh. Last the flux of the metallic substances, which is of sub-nitrate of bismuth, obtained by decomposing in water the nitrate of the acid of bismuth, to which is added 1-12 of borax.”
These fluxes are mixed with the basic oxyds in greater or less proportion, according as the colors are intended for work, which will require a greater or less degree of heat in firing.
Underglaze colors in powder suitable for painting on pottery, can be procured of several different manufactures. As mentioned before, the variety of these colors is not so great as is to be found in overglaze colors, but as they can be readily mixed the number is sufficient for all practical purposes.
In my own work I have made almost exclusive use of French colors, those manufactured by M. Lacroix. These colors are finely ground and of considerable variety of tint. A list of those which have been tried and found to give satisfactory results, may be given here:
Blues—Bleu de Roi (King’s blue).
Bleu violacé (violet blue).
Light blue—Bleu myosotis (Forget-me-not blue).