COLOURED CLASSES OF THE ANCIENTS. 229 



Silex - - Ca) - 142 grains. Compofitlon of 



Oxide of Lead - (b) - 28 she red glafs. 



of Copper (d) - \5 



of Iron - r/; - 2 



Alumine - - (e) r 5 - — — . 



Lime - - (cj - 3 — — 



195 

 On comparing the external chara6lers of this red glafs-pafte It was probably 

 with the cupreous fcoriaj of a lively brown-red, fuch as is\o"^w°k 

 fometimes obtained on melting copper ores, it is rendered 

 highly probable, that the ancients did not compound (he above 

 pafte diredly from its fimple conftiluent parts, but inftead of 

 them have perhaps employed copper fcoria?. On that fuppo- 

 fition they had nothing more to do, than to feled the beft co- 

 loured pieces to fufe and caft them into plates. 



ir. Antique Green Glafs-Pajle. 



The colour of this green parte is a light verdigris. Its mafs. Antique green 

 like that of the preceding, is opake, and of a fcoriaceous fplen- ^}^^^: opakc. 

 dent fracture. §• ?• 



For its chemical analyfis I employed tivo hundred grains, 

 which, having been treated in exactly the fame manner as the 

 foregoing, I found to confili of the following ingredients: 



Silex - - - 130 grains. Component parta 



Oxide of Copper - - 20 of the green 



.T J . . 25 enamel; 



Iron - - , 7 



Lime - - ? 13 n 



Alumine - - - 11 



196 grains. 



This green glafs-pafte, then, contains the fame conftituent j^j^p^ ^^jy jj^ 

 parts as the red, only in different proportion?, 3oth receive proportion of • 

 their colour from copper ; But the reafon \yhy this metal pro- 1^^^^^,/°" * * 

 duces in the one.a red, and in the other ^ green colour, de- 

 pends on the different degrees of its oxidation or faturation 

 with oxigen. 



It is one of he chemical properties of copper, that in the 

 IJjite of a fub-Qxide, that is only half faturated with oxigen, 



■ -■■ — ^ if 



