G L A

G t A

( 511 )

that is by carbonizing a glafs containing theoxyds of iron and copper. The colour was alively copper-red, perfectly opake and bright atthe point of fradture. The earthy and metallicparts of 400 grains, as given by analyfis, wereas follows:

Silex - - - - -

142

Oxyd of lead - -

28

Oxyd of copper - -

*5

Oxyd of iron - -

2

Alumine - - - -

5

Lime -----

3

*95

It is obfervable that this was opake, whereasthe former mentioned glafs is tranfparent.Klaproth conjectures that this antique glafswas made not by any intentional proportion orfelection of ingredients, but from the fcorite offome copper ores.

Of Green Glajfes. For thefe, which are in-tended to imitate the emerald when full-bodied,and the aqua-marine when light, there aremany receipts.

Among others the following may be feledted.Take 160 parts of any glafs bafis into whichmuch lead enters, as the glafs No. 1, 2, 3, or5, mix it with 4 parts of the oxyd of copper madeby Ample calcination, and -jV of a part of anyoxyd of iron, and melt with a fufficient heat.In this as in all the other emerald colours avery fmall addition of iron feems highly ufe-ful to give fomewhat of a richnefs of tint, andto take away the cold hue of the copper alone.For this reafon too the rich yellow of the leadis of fo much advantage.

Another is, 576 parts of the glafs bafis, 6 ofthe fame oxyd of copper, and only of oxydof iron. Another is, 200 parts of fine fand,400 of minium, 8 of calcined verdigris, and r.of oxyd of iron. The variation in thefe pro-portions is extreme.

Another method of compofing the emerald-green is by a mixture of blue and yellow glafsin due proportions. The yellow may be givenby the oxyd of antimony, and the blue bycobalt. Fontanieu gives for this 120 parts ofany of the glafs bafes, 1 of mountain blue, andtV glafs of antimony: or elfe 57 6 parts ofthe glafs No. 2, 20 of glafs of antimony, and 3of oxyd of cobalt (not zaffre).

When the green has a fenfible mixture ofblue in the tint it forms a fine fomewhat coldcolour refembiing the aqua-marine. This isproduced in general by adding cobalt in fome

form or other to the materials for the greenglafs. For this the following receipts are givenby Neri, Kunckel, and Fontanieu. Melt 300parts of any fine cryftal glafs made withoutmanganefe,. add thereto at intervals 6 parts ofcalcined copper or any fimilar preparation, and4 of a part of zaffre, ftir the glafs well whilemixing, and then let them fufe quietly for fomehours. No reafons appear however why thewhole materials fhould not be mixed at firft asin the ufual mode. Another is, 300 parts offine foda glafs with 6 of calcined brafs, meltedtogether, ftirred twice at long intervals, theheat being continued a long time, and finallyfuffered to remain in quiet fufion for manyhours before working. Another is, 256 partsof fine glafs, and 150 of litharge or minium,firft melted together and well mixed (or elfeany of the glafs bafes already mentioned thatcontain lead), to which is added 4 parts of cal-cined brafs or of oxyd of copper made by cal-cination, and \ a part of zaffre. Another re-ceipt for this colour is a mixture of yellow andblue, in fuch proportions that the blue {hallprevail a little over the perfect green, the natu-ral refult of the mixture of blue and yellow.This is done by adding to 24 parts of the glafsbafis No. 1 or No. 3, i-j part of glafs of anti-mony, and T V of a part of oxyd of cobalt.

According to Klaproth ’s analyfis of a portionof an antique verdigris-green opake glafs, thecolour was formerly, as now, given by copperand a fmall portion of iron, the fame in kind,as thofe that compofed the red glafs above men-tioned, and probably alfo the oxyds were notartificially mixed but were ufed as contained ina natural ore. Two hundred grains of tills,green glafs or pafte yielded

grains

Of Silex - - - - 130

Oxyd of copper - 20

Oxyd of lead - 15

Oxyd of iron - 7

Lime - - - - 13

Alumine - - - 11

196

Of Blue Glafs. Thefe glaftes, which areintended to imitate the fapphire, are compofedof a common bafis and coloured with cobalt,but generally with the addition of a quantity ofmanganefe, which by adding a violet tint givesa greater richnefs of body. When the manga-nefe is in large proportion, the colour then is arich violet blue or purple reiembling the ante*