20 ON PLATE-CASTING. 



the reverse impression taken. The moulds are 

 then separated (channels for the molten gold 

 cut), again dried and adjusted, and the gold 

 poured, a much larger amount of metal being 

 melted than the actual weight required for the 

 plate ; the proportion being twenty times the 

 weight of the wax plate, the weight of the column 

 of gold being of essential service in forcing the 

 metal into every crevice of the mould, and in pre- 

 venting air-bubbles. The rough edges are now 

 taken off, and the plate fitted down to the model, 

 much in the same way as an ordinary ivory piece. 

 I have also used a hard plaster-and-sand model 

 to burnish the plate on, and to assist in correct- 

 ing irregularities. Lacing the plate will be also 

 found useful. From the approximate results of 

 several measurements, I assume that the contrac- 

 tion of 18 -carat gold is one- sixtieth of the mean 

 breadth of the plate ; hence, scraping the model 

 with a sculptor or graver evenly over its surface 

 before the wax plate is made will compensate for 

 the contraction of the metal on cooling. I am 

 not acquainted with any solvent that will answer 

 equally well. 



" Nos. 1, 2, and 3 were some of the first plates 

 cast to ascertain how thinly they could be pro- 

 duced, and also, in the event of their requiring 

 much finish, the advantage of having a thick 

 plate, to be reduced in fine fitting. 



" No. 4. A piece fitted to the model with bands. 



