By Mark Parmenter
This short tour is to explain how to make a wax impression from a mold taken from life for the purpose of casting it in bronze using the lost wax casting. The molding process is called "life-casting" or "body-casting". This process is explained in detail HERE and in numerous books and videos.
In brief, a mold is taken directly from a model using plaster, dental alginate or special silicones. A great degree of detail and accuracy is achieve using this technique.
Generally, a positive is made from the mold using plasters or polymer resins by the artist. While generally permanent, these materials do suffer longevity and are fragile. Casting in bronze or aluminum is a natural choice to increase value, longevity and durability. Metal casting also opens choices for compositional extension and placement in outdoor settings. The intrinsic value of metal, especially bronze, will certainly increase the profitability of the work to the artist and the long term investment of the collector. Granted, metal casting is expensive, but we have found that the initial expense is more than offset by higher selling prices for the reasons given above.
The life-cast artist does have certain advantages over the traditional modeling techniques. The life-caster has a mold and knows how to get a positive casting from that mold. Generally in the traditional method a mold must be made from the clay model to obtain a wax positive suitable for casting. The mold making process typically costs 20% to 25% of the total casting process. Wax working is another cost that can be eliminated by the life-caster, another 5% of the casting cost. In this article, I will explain my method for obtaining a good wax impression from a life-cast mold and some general wax working techniques. I will not attempt to explain the lost wax casting process, as this is explained elsewhere and is beyond the scope of this article. For a general overview look HERE and follow the tour.
OK, let's get down to business.
The mold:
This mold is made from medical plaster gauze strips. I use plaster strips because I am not real concerned about getting every pore of the skin. Those that use alginate/plaster systems or silicones can follow the same steps. Alginate is very receptive to a wax impression. Waxes can be made quickly so no drying problems are encountered. I many cases multiple waxes can be made from the same alginate mold. For closed molds, such as a hand or feet, a wax impression can be made by filling the mold cavity with molten wax and dumping out the bulk when a suitable thickness is achieved. Bronzes are cast hollow and need to be 3mm to 6mm thick.
Another view of the mold.
