292 CEMENTS. 



When it is hard, raise the isinglass up with the 

 point of a penknife, and it will fly off like horn, 

 having a sharp impression of the medal. 



The isinglass may be made of any colour by mix- 

 ing the colour with it; or you may breathe on the 

 concave side, and lay gold leaf on it, which, by 

 shining through, will make it appear like a gold 

 medal. But if you wish to imitate a copper medal, 

 mix a little carmine with the isinglass, and lay gold 

 leaf on as before. 



CEMENTS. 



Cements require to be of various compositions, 

 according to the substances to which they are ap- 

 plied, and whether they are to be exposed to heat 

 and moisture. 



Common Glue. 



Common glue is formed by extracting by boil- 

 ing the gelatinous part of cuttings or scraps of 

 coarse leather, or the hides of beasts. It is then 

 poured out in thin cakes and dried. 



Isinglass Glue. 



Isinglass glue is made by dissolving beaten isin- 

 glass in water by boiling, and, having strained it 

 through a coarse linen cloth, evaporating it again, 

 o such a consistence, that being cold, the glue will 

 be perfectly hard and dry. 



This cement is improved by dissolving the isin- 

 glass in any proof spirit by heat, or by adding to it 

 when dissolved in water, an equal quantity of spirits 

 of wine. 



