400 On the Composition of the Enamel . 
must be prevented by mixing with them other substances, 
such as refractory earths, or metallic oxyds difficult to be 
fused. 
The metallic calces which form the bases of the yel- 
low colours are generally those of lead ; as minium, the 
white calx of lead, or litharge, the white calx of antimo- 
ny, called diaphoretic antimony: that called crocus me- 
tallorum is also employed. This regains, pulverised and 
mixed with white oxyd, gives likewise a yellow. The 
following are the different compositions used : one part 
of the white oxyd of antimony, one of the white oxyd of 
lead (or two or three); these doses are exceedingly varia- 
ble; one part of alum, and one of sal-ammoniac. When 
these matters have been all pulverised, and mixed well 
together, they are put in a vessel over a fire sufficient to 
sublimate and decompose the sal-ammoniac; and when 
the matter has assumed a yellow colour, the operation is 
finished.* The calces of lead mixed in a small quantity 
either with silex or alumine, also with the pure calx of tin, 
exceedingly white, give likewise yellows. One part of 
the oxyd of lead is added to two, three, or four of the other 
substances above mentioned. In these different composi- 
tions for yellow, you may use also oxyd of iron, either 
pure, or that kind which has been prepared with alum 
and vitriol of iron : you will then obtain different shades 
of yellow. From what has been said, you may vary these 
compositions of yellow as much as you please. Yellows 
require so little flux, that one or two parts, in general, to 
one of the colour are sufficient ; saline fluxes are improper 
for them, and especially those which contain nitre. They 
must be used with fluxes composed of enamel sand, oxyd 
of lead, and borax, without marine salt. 
(To be concluded in our next number?) 
* This in colour-shops is called Naples yellow. 
