BLOCK PRINTING, &C. 195- 



^mploved ifor the fabrication of assignats, and may be esteemed — used in fabri- 



^ , -Kr r< \ -iix-i- 'Cating assig- 



tlie foundation of the stereotype art. M. Erhmann will testify j^^tg^ g^d the 



jl -g foundation of 



- , » J , , stereotypes. 



In making stamps with moulds of plaster, the success de- T^e most fusi- 



pcnds greatly on the fusibility of the metal*; that employed bv"^'*' known. 

 M. Darcet is the most fusil)le known. 



*' Numerous experinnents," says M. Darcet, " convinced 8 parts bis- 



^ , 1 . • , muth, 5 lead, 3 



my father, that the compoxind should be f(jrmed of eight parts ti,,, melts 13 

 of bismutn, five of lead, and three of tin. Wlien it is well ^e-^ees below 

 ^ , • , , boiling wat<fr. 



made, it begms to soften at 91° of the centigrade thermometer 



(196° Farht.), and melts between 92" and 93** (about 199° 

 Farht.). 



*' This compound when cold is sufficienily malleable to' Sufficiently 

 stand a blow, and hard enough to preserve the impressions from ^^^^^ 

 friction, and to allow them to be retouched with the graver. 



•" The following is the best mode of preparing it : 



''' Fuse the bismuth, cover it with resm or suet, and heat Mo.d,e of pre - 

 the whole rather strongly ; add the lead, stir them well toge- P'^'''"^ ? • 

 ther, increase the temperature a little, and add to the metals 

 in fusion the requisite quantity of tin. Sl:r tiie mixture again, 

 Ki\(\ cast it into a plato or ingot, 



" This coiTipound is to be used only in the soft state, that To be used 

 is, zt a degree of heat much below the point of boiling water ; ^"'^ ^^^'^" 

 it is then fitted for receiving the impression of the matrix, with- 

 out emitting the air and water this contains^ which would form 

 blebs or flaws in the stamp. 



" The soft state is that which th« fusible metal assumes at Birections for 

 91°(196"FtiAt.). When it begms to grow solid, ;^ crystal- "^''^^ ''* 

 tzation forms in tiie still fluid mass of metal ; and this crys- 

 tallization must be broken and rendered confused, by agitat- 

 ing the metal as quickly as possible, kneading it as it were, 

 and particularly by bringing the part near the edges to the 

 eentre, and alternately carrying the central part to the edges. 



" When the whole of the metal is reduced to this state, no- 

 thing more is necessary, but to stamp it quickly with the plas- 

 ter matrix. 



" Every time this compound is fused, oxided pellicles Scorise, 



'are formed on its surface ; and the greater heat, or the longer 



it is continued, the more considerable they lare. These scorias 



fahould be collected together, and afterwards fused with resin, 



C c 2 oil, 



