MAKING MOULDS AND CASTS. 



265 



Great care is necessary to avoid breaking the cast, which of 



course is very easily cut or broken. In cutting off the pink 



lining be exceedingly careful 



not to go too deep (Fig. 65). 



The purpose of this lining is 



to show you when you are close 



to the cast. If the case of the 



mould is quite thick, hold the 



chisel on a slant of about fifty 



degrees from a perpendicular, 



and pare off the upper surface 



gradually. 



MAKING GELATINE MOULDS. 

 There are many 

 objects which can 

 not be copied in 

 plaster by either 

 of the above meth- 

 ods without great 

 difficulty. These 

 are hard s u b- 

 stances, the sur- 

 faces of which are 

 extremely irregu- 

 lar and full of lit- 



tle hollows, such 



FIG. 65. Chiseling off the Waste Mould. 



as meteorites, statuettes, sculptured rocks, or models such as 

 those of the Aztec calendar stone and sacrificial stone. "When 

 a number of copies are required, the making of a waste mould 

 for each copy is out of the question, and the manufacture of a 

 piece mould that will draw off is also a long task, to say nothing 

 of making the casts themselves and cleaning them up. The so- 

 lution of all such difficulties is the gelatine or " glue " mould, 

 w T hich is elastic, pliant, and yet keeps its shape perfectly. This 

 is how to make it : 



Let us suppose we are to make a gelatine mould of a flattened 

 meteorite, eight inches in diameter and about three inches 

 thick. Take some potter's clay, or modeling clay, which has 

 been nicely worked up in a square lump, and is not wet enough 



