THE PROPERTIES OF MODELLING-GLUES 273 



cold, the difficulty of getting such an object as a large coiled 

 snake out of its mould is almost insuperable, owing to the 

 resistance and want of elasticity of such a large mass when 

 lying in undercut folds, each fold in that case blocking the 

 other ; whereas, when made hollow, the folds are compressible 

 when being skinned out, as it were, from the mould. Not 

 only that, but there is danger of future deterioration or cracking 

 in thick masses of composition, unless, probably, protected by 

 pigment within or without. 



It may be safely affirmed, therefore, that, even if the 

 coating of composition is so thin that every detail of the 

 mould can be clearly seen through it, it will be thick enough, 

 provided it delivers without tearing ; breaking is a sign of bad 

 materials, and is quite different from tearing. 



When models are accidentally made too thick, as they 

 often will be in certain places, they may be further hollowed 

 with a knife or scissors ; fins also may be cut thinner and 

 pared. 



The method of applying the compositions, when small 

 objects are cast solid, is simply to introduce them by means of a 

 spoon or brush into the hollow mould, and turn this about until 

 the composition runs into every crevice, and, when the mould 

 is full, set it in some cool place to allow its contents to solidify. 

 Very small objects will be fit to remove from the mould in a 

 couple of hours, but such a thing as a common ringed snake is 

 better left all night before being taken out. Figures 4 and 5 

 on Plate XV. represent such an object coiled and extended. 



When, however, objects are cast hollow — which should always 

 be done, and can be done even when they are small, but is 

 absolutely necessary when they are of any size, — the method of 

 procedure is, first to warm and oil the mould slightly, then 

 pour into it a sufficient quantity of the composition to form 

 a thin skin over all. This quantity, which experience alone 



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