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Casting Sculpture in Metal

A short explanation of the Lost-wax casting Method

as it relates to

Silver Sculpture

Gordon Lochhead explains something of the way he makes his silver sculpture.

Most of the pieces shown on these pages were first modelled in wax, based on drawings notes and photographs. Alternatively, the wax might be cast in a rubber mold, made from an earlier metal cast or from a model made in clay or some other material. This is then used as the pattern for a lost-wax casting in silver. The essence of this method is to attach tubes of wax to the model which will act as the forms for channels to allow molten metal to run in, and hot displaced gases to escape. Round this assembly a refactory mold is made, and then the mold is fired in a kiln to melt out the wax, dry out all water, and finally burn away the wax residue which has soaked into the mold material as a hot liquid. When the mold is ready, the silver (or bronze or whatever other alloy is used) is melted in a furnace, in the case of silver to about 1050 degrees C, and poured into the mold. When cooled sufficiently, the mold is broken away, the casting cleaned and the sprues cut away.

The casting

Two sizes of casts of the Loch Lomond International golf trophy, just cast and cleaned but before removing the sprues. When the piece was cast, the conical shape at the bottom was the top of the mold where the metal was poured into the tapering cup, and it ran down the thicker tubes into the cavity of the mold. the thinner tubes are the vents which allow the hot gases to escape upwards. Trapped gas is one of the commonest causes of flaws in castings

.

Finishing

The as-cast surface of the metal can be very pleasing, but it is very hard with most forms to avoid some intrusion of sprue ends, and various flaws, imperfections, or deliberate unfinished surfaces need filing, grinding, chiselling, scraping, burnishing or polishing to achieve the desired finish. Unlike cast bronze sculpture, silver work is usually finished as polished, unpatinated metal, and this often requires many hours of skilled chasing and polishing work.

The finished casting, a replica of the Loch Lomond International Challenge Golf Trophy . Each year, the winner of the competition is given one of these full-sized replicas to keep.