The assembled trees are put into steel flasks and are ready to invest.  In this process, a quick-setting plaster is mixed and poured into the flasks, surrounding the wax.  The wax trees have been dipped in a special lubricant which helps the plaster completely coat the models, reducing the amount of air that can be trapped in between wax and plaster, and thereby reducing the chances of a failed casting.

 

 

 

 

When the plaster is completely hardened, the flasks are put into a steam de-waxer.  This causes the wax to melt out of the plaster, leaving behind negative space in the shape of the pieces, which in casting will be filled with the molten metal. 

Dewaxing also helps to cure the plaster.  It is important that the plaster molds be completely dewaxed.  If any wax were to remain in the flask, it could interrupt the flow of metal and produce a bad casting.  The next process, however, prevents this from happening.

 

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