COLOURED GLASSES OF THE ANCtENTS. 227 



only fubftances capable of producing fuch an efFedl. But It 

 would be a problem of difficult folution to determine, what 

 were the means and procefiTes employed by the ancients for 

 this purpofe, as they had no acquaintance with the mineral "^^""gJ^ *s ^n- 



• 1 I • 1 r /■ II 1 1-1 cients were ig- 



acids, which, at prelent, are ufiially employed in the prepa- norant of our 



ration of metallic oxides. It is neverthelefs certain, that the mineral acids, 



art of giving many various colours to glafs muft, at leaft in ]ou?^d"pafteTln 



later times among the Greeks and Romans, have reached an high perfeftion, 



eminent degree of perfedbn ; for they knew how to imitate, 



by their partes of glafs, even thofe gems which have a deep 



colour, fo as to deceive the eye vei-y confiderably, A proof 



of this, among others, is afforded by the following words of 



Pliny *, relating to the artificial imitation of the carbiinde, a 



gem then in the higheft eftimalion : " Adulterantur vitro findU 



lime : fed cote deprehenduntur, ficut alice gemmce fa6lili(B." 



It was in the time of Auguftus that the Roman architeds Roman mofalc 

 began to make ufe of coloured glafs in their mofaic decora- ^ ^ ^ * '*' 

 tions, befides the feveral fpecies of marble and other coloured 

 ftones, which, before, were ufually employed with that de- 

 sign. Such an application of the glafs-pafles was reforted to 

 in a villa built by the emperor Tiberius on the ifland of Capri, 

 as is (hewn by fpecimens lately found among its ruins. I fub- 

 jeded forae of thefe in my pofTeffion to chemical analyfis, 

 chiefly for the purpofe of difcovering what metallic fubflances 

 the ancients employed to tinge thofe varioufly coloured raafies 

 of glafs. 



I. Antique Red Glafs. 



The colour of this glafs-pafte is a lively copper-red. The Antique red 

 Jnafs is perfectly opake, and very bright at the place of recent s'^^^J ^P*^*' 

 fradure. This is probably the very fame glafs, of which Pliny 

 fays : * ** Fit el totiim rubens vitrum, atque nan tranjlucens, 

 lieematinon adpellatum." 



(a) Tivo hundred grains of this red glafs were finely tritu- Analyfis, 200 

 rated, and, together with 400 grains of caupc potajh, ignited g»-ains, tritu. ated 

 for half an hour ; by which management the mixture foon en- 400 gr. potafli ; 

 tered into a thin fufion. After cooling, the whole mafs was 

 foftened with water, then fuperfalurated with muriatic acid ; foftened with 

 and, after this mixture had been again infpilTated to a faline ^^^'^^^ > fuperfa- 



' 01 turated with 



•Lib. XXXVII. Cap. 26. Z^S!^^' 



difFufed in much 

 Q 2 raafs, hot water. 



