230^ COLOURED GtASSES OF, THE ANCIENT3. 



it produces a copper-red enamel; while, on the conlraf),, 

 when perfedtly oxided or full)' faturated with that acidifying 

 principle, the enamel which it yields is green. Pliny men- 

 tions feveral preparations of copper that were in ufe in his 

 time ; he only dwells too long on enumerating their pretended 

 medicinal virtues. Of fuch artificial preparations of copper 

 fome might have been ferviceable in making green glafs- 

 paftes, in the cafe that, perhaps, the native oxides of copper, 

 of which in particular the copper-mines on the ifland of Cyprus 

 could afford copious quantities, were not then employed for 

 this purpofe. 



III. Antique Blue Glafs. 

 Whetherthe an- My leading objeft in chemically decompofing this glafs, was 

 gurbrcobdu ^^^ folution of the queftion : What was the colouring matter 

 which the ancients employed in order to tinge their glafs blue? 

 The ftriking fimilarity of the colour of the blue antique glafs 

 to that of our modern, which, as is well known, is tinged by 

 means of cobalt, has induced feveral learned men to conjec- 

 ture, that even the ancients muft have been acquainted with 

 this foffil, as well as with its properties of colouring glafs blue. 

 This was, likewife, the opinion of Ferber, when in his Letters 

 The affirmative /ro?n Italj/, page 114, he fays; " In the villa Adriani near Ti- 

 genera y, ^^^^.^ ^^^^ Frefcati, and in feveral places, antique niufaic uorks 



hare been found which exhibited fome cubes of a blue vitreous 

 compofilion, and ferve as a proof, that the ancients mvfi have 

 known the vft of cobalt and the preparation of fmalt." This 

 opinion he repeats in various places, 

 but erroneoufly This opinion being fupporled by no chemical proof, refts 

 folely on the Aippofilion, that cobalt is the only fubftance 

 which is capable of affording a blue enamel. However, it is 

 certain the ancients knew the art of giving, by means of iron, 

 a blue colour to glafs refembling that which we produce by 

 cobalt. 

 The contrary A chemical demonllration of this fad has been given by 



Cmclin^ Gmelin of Gottingen, in his Chefnical Examination of a Blue 



Glafs from an antique Mofuic Fragment *, which was found in 

 digging a garden at Mumpelgard, and is probably of Roman 



* Commentat. Gotting. Vol. II. 



origin. 



fuppofed. 



