COLOURS OBTAINED FROM METALLIC OXIDES. 105 



Colours for enamel painting have been longeft known : the Enamel colours 

 receipts in the works I have mentioned at the beginning of %*™J^ n long 

 this eifay all relate to thefe colours. 



It is known that enamel is a glafs rendered opake by oxide Enamel is glafs 

 of tin, and very fufible by the oxide of lead. It te<*hi& kft£ y ^^^ 

 which in particular gives it properties very different from opake by ox. tin. 

 thofe of the other excipients of metallic colours. Hence all the 

 glades and glazes that contain lead, have the properties of 

 enamel, and what we may afTert of the one, will apply to the 

 other with very little difference. 



Such are the white and tranfparent glazes of Dutch or Delft It is the glaze of 

 ware, and the glaze of the porcelain called foft (tendre.) 



This porcelain, the firft made in France, particularly at Soft porcelain of 

 Sevres, and indeed for a long time almoit exclufively at this evre5 » 

 manufactory, has for its bafe a vitreous frit nearly opake, ca- 

 pable of being acted upon by marl, and its glaze is a very 

 tranfparent glafs containing much lead. 



The colours made ule of are the fame as thofe for enamel- Colours the 

 ling, consequently the changes thefe colours undergo in ena- ^Jj ** ° r Cna " 

 mel, mutt take place in this fpecies of porcelain, becaufe, as 

 we fhall foon fee, the caufes of the change are the fame in 

 both. 



The colours for enamel and tender porcelain require lefs Thefe require 



flux than the others, becaufe the glafs on which they are le u fs fl , ux b . ecaufe 

 . the glaze is very 



placed, foftens fufficiently to be penetrated by them. fufible. 



This folvent may be either the mixture of glafs of lead, and The flux before 

 pure lilex called rocaille, or this fame glafs mixed with that mentioned. 

 of borax. 



Montamy fays that glafs of lead ought not to be ufed in the 

 flux for enamel ; he employs borax alone. He then dilutes 

 or makes up his colours in a volatile oil. 



On the contrary, the painters of the manufactory at Sevres, Glafs of lead Is 

 ufeonly colours without borax, becaufe they dilute them with a S°° d material, 

 gum, and borax does not dilute well this way. I am con- 

 vinced that both methods are equally good, and that Montamy 

 is not juftified in excluding the fluxes of lead, as they are em- 

 ployed without inconvenience every day, and even render the 

 management of colours more eafy. 



I have remarked, that in the baking of thefe colours the The foft glaz« 



glaze is foftened fo much as to be eafily penetrated by them ; , very much dl " 

 i • • r ,. i i i . r™ , lutes thc c °- 



this is one great caule 01 the change they undergo. 1 hey be- i eurs , 



4 come 



