Crystalline Substance from the Zinc-foundry at Filisur. 403 



lingfleet. — I have found the colouring matter of these beads to 

 be coppei*. At the present day cobalt, I believe, is exclusively 

 employed to produce every shade of blue glass, copper being 

 only used in staining it red or green ; and I imagine that a 

 modern artist would be much at a loss to obtain the fine azure 

 of these beads from copper. I find that a blue glass may be 

 obtained from copper by employing a large proportion of car- 

 bonate of soda in the composition, and I suppose that the blue 

 colour in this case is given by the carbonate of copper, as the 

 red is by the protoxide. I did not succeed, however, in ob- 

 taining a good permanent glass, and have reason to think that 

 considerable nicety is required in the proportions, to bring the 

 process to perfection. Now we know that the Romans pos- 

 sessed the art of making a blue glass coloured by copper. 

 Among the most curious remains found at Pompeii were the 

 contents of a coloui'-shop, which were analysed by Sir Hum- 

 phry Davy ; and in the blue frit which he examined, that la- 

 mented philosopher found the colouring matter to be copper. 

 I have lately had occasion to show in another instance, that 

 antiquarian pursuits, however far they may appear to be dis- 

 joined from experimental philosophy, may sometimes derive 

 aid from an alliance with it. I pointed out, in a piece of black 

 pottery, angular and unaltered fragments of calcareous spar 

 forming a part of its constituent ingredients, and inferred 

 from hence that this pottery could not have been baked in the 

 usual degree; and I stated that this was that black pottery of 

 the Romans which we meet with at many of their stations, 

 and which a German chemist has shown to have been pro- 

 bably made of clay kneaded with bitumen or pitch, and after- 

 wards charred in a moderate heat. Now it is obvious that 

 wherever an antiquary should discover the fragments of a 

 pottery manufactured in so peculiar a manner, he would not 

 require to know the form of the vessel, or to decypher the 

 name of the artist, but could pronounce at once that the arts 

 of Rome had penetrated to that place. An inference of the 

 same kind I am disposed to draw from the colouring of these 

 glass beads. The date of the tumuli in which the beads were 

 found is in question. The j)ecaliar manner in which the glass 

 is coloured, determines me to believe that the tunuili, to- 

 gether with ti)e implements wiiich they contain of a more 

 equivocal character, and with whatever peculiarities ni tiic mode 

 of sepulture we may discover in tlu.m, are of a date posterior 

 to the introduction of the Roman arts into Britain. 



Since this paper was read, I have ibund among the ashes 

 contained in a Roman cinerary urn, of black pottery, a iVag- 

 mcnt of a blue glass bead precisely similar to those whicli 

 were discovered in the tumuli by Mr. Siillinglieet. I have 



?< F 2 al^o 



