1* J(efearchcs reJpcEiing the 



which may be direftly obtained from (ilver. The corrlponnd 

 yellows are obtained in confequence of the fame principles as 

 the red colour of iron. For this purpofe we employ metallic 

 oxyds, the vitrification of which muft be prevented by mixing 

 with them other fubftances, fuch as refra£lory earths^ or me- 

 tallic oxyds difficult to be fuied. 



The metallic calces which form the bafes of the yellow 

 colours are generally thofe of lead j as minium, the white 

 calx of lead, or litharge, the white calx of antimony, called 

 diaphoretic antimony : that called crocus metallorum is alfo 

 employed. This regulus, pulverifed and mixed with white 

 dxyd, gives likewife a yellow. The following are the dif- 

 ferent compofitions ufed : one part of the white oxyd of an- 

 timony, one of the white oxyd of lead (or two or three) > 

 thefe dofes are exceedingly variable; one part of alum, and 

 one of fal-ammoniac. When thefe matters have been all 

 pulverifed, and mixed well together, they are put in a veflel 

 over a fire fufficient to fublimatc and decompofe the fal-am- 

 moniac ; and when the matter has affumed a yellow colour, 

 the operation is finiflied*._ The calces of lead mixed in a 

 fmall quantity either with filex or alumine, alfo with the 

 pure calx of tin, exceedingly white, give likewife yellows* 

 One part of the oxyd of lead is added to two, three, or four 

 of the other fubftances above mentioned. In thefe different 

 compofitions for yellow^ you may ufe alfo oxyd of iron, either 

 pure, or that kind which has been prepared with alum and 

 vitriol of iron : you will then obtain different fhades of yel- 

 low. From what has been faid, you may vary thefe com- 

 pofitions of yellow as much as you pleafe. Yellows require 

 ib little flux, that one or two parts, in general, to one of the 

 colour are fufficient; fallne fluxes are improper for them, 

 and efpecially thofe \\hich contain nitre. They milft be 

 ufed with fluxes compofed of enamel fand, oxyd of lead, and 

 borax, without marine fait. 



A yellow may b« obtait^ed alfo direftly from filver. AH 



thefe mixtures may be varied, and you may try others. For 



this purpofe you may ufe fulphat of filver, or any oxyd of 



that metal mixed with alumfine or file.x, or ex-en with both, 



• This in colour-fliops is called Naples vellow. 



ia 



