A wax suitable for casting in bronze should be hollow whenever and wherever a cross section exceeds 1". Ideally the thickness of the wall of wax should be between 1/8 and 1/4 of an inch. If any artist wants to cast his or her own wax as a means of reducing the overall cost of the bronze casting, here are some helpful tips to obtain a good wax cast.
The wax used for painting the fidelity coat into the rubber mold should be at 300+ degrees F; the wax for slushing the mold should be around 180 degrees F. Have another can where wax can be segregated and cooled to a gooey state for reinforcing high edges in the mold.
Preparing the mold
--Release the plaster flanges of each part of the plaster mother mold by brushing them with kerosene.
--Before painting the fidelity coat release the rubber surface (negative) with mold release or PAM (use the latter very conservatively because PAM is very oily).
Painting the fidelity coat
With a well-loaded natural bristle brush cover a small area at a time with very hot wax, without over brushing, to avoid trapped bubbles. On a deeply- textured surface it is a good idea to use a hot metal tip (a thick piece of wire will do) to burst trapped bubbles.
Paint a second coat of wax over the fidelity coat with wax around 180F making sure no air pockets are created between coats. Then proceed to "hang" the gooey wax on top of higher edges and also the area opposite to the pour opening, because these areas will wash off as the slush wax runs to fill/empty the mold.
Slushing the Mold
Before closing the mold, the edges (seams) of the rubber mold sections must be cleaned using a hot tool; any spills or drips on the plaster flanges that will be touching each other should also be removed to ensure a tight closing. When the mold is clean and ready to be closed make sure to apply talcum powder on the rubber seams to facilitate the closing and avoid pinching between opposite sides of the rubber which will cause an off set in the seam line. Close the mold and fill it with 180 degree F wax, leaving it in for a few seconds so as to form a thin additional film over the fidelity coat, then empty the wax from the mold and allow the wax in the mold to get cold before removing the wax positive from the mold.
Coryat Casting Co. Inc., 3346 Rt 9G, Rhinebeck N.Y. 12572
Tel: (845) 876-2553 Fax: (845) 876-0783