The creator of the casting "master" has not only to consider the aesthetics of the design but has also to think carefully about, and be familiar with, the physical facts of the process by which it will be reproduced.

These are, principally:

? Dimensional shrinkage which occurs during vulcanisation of the rubber mould, during solidification of the wax pattern and during solidification of the cast metal

? Differing thicknesses of section with respect to the cooling and solidification of molten metal

? Correct feeding of the molten metal and the location of the feed sprue or sprues without ? ideally altering the aesthetics of the piece.

? Ease of finishing the final casting. Most expensive jewellery castings are mainly hand finished, but volu

me production items tend to be finished by a variety of automatic processes. The master pattern maker may employ several techniques for the creation of his models, for example, by employing existing pieces, by fabricating in metal or by wax carving using one of the special carving waxes available.

The master pattern must always be produced to a very high standard of finish, since this will determine the quality of the resulting casting and lengthy and expensive finishin

operations will be reduced to a minimum. Thus, excessive loss of precious metal can be avoided in these operations. When the master pattern is complete, a rubber mould is made as detailed in the next section.