Permanent Colours of Opake Bodies. 171 



Thefe experiments fhew, that Tranfparent 

 Coloured Liquors do not yield any colour by 

 refledion, but by tranfmiirion only. 



If thefe liquors are fpread thin on any white 

 ground, they appear of the fame colours, which 

 they had exhibited, when viewed in the necks of 

 the vials j as the light refleded from the white 

 ground is, in this cafe, tranfmitted through the 

 coloured medium. 



But when they are fpread upon a black ground, 

 they afford no colour. The black ground, how- 

 ever, fhould not be a polifhed body; as the 

 light, refledled thereby, would be tranfmitted 

 through the thin medium on its furface, and be 

 tinged by pafilng through it, 



1 fliall now proceed to relate feme experi- 

 ments, which were performed with tinged glaiTes; 

 thefe being, in many rcfpeds, analogous to co^ 

 loured liquors. 



I made feveral parcels of colourlefs glafs. That, 

 which I principally employed in thefe experi- 

 ments, confided of equal parts of borax and 

 white fand. The glafs was reduced to powder, 

 and afterwards ground, together with the ingre- 

 dients by which the colours were imparted. 



This method, of incorporating the tinging 

 particles, is greatly preferable to mixing them 

 with the raw materials. The glalTes, thus com- 

 pofed, excel mofl: others in hardnefs, and are 

 fiarccly inferior, in luflre, to real gems. 



All 



