Illustration: Uto Hogerzeil
Lost Wax Casting
Lost wax casting, often referred to in its French form cire perdue can be traced back to 3500 B.C. in Mesopotamia. The earliest castings were made from copper, a soft and malleable metal. The metalsmith soon found that a combination of metal ores, such as copper and tin, would create a hard-wearing metal alloy with multiple uses from the functional to the decorative.
The first written account of the lost wax casting process comes from Theophilus in twelfth century Germany. In his detailed description of a monastic metalsmithing workshop and the techniques they employed, Theophilus chronicles the lost wax casting process used to form silver handles for a chalice around the same period that monastic metalsmiths were creating the Cross of Cong and St Manchan’s shrine in a Roscommon monastery.
… take some wax and shape handles out of it and carve on them snakes, animals, birds, or foliage in any way you wish. On the top of each handle put a small piece of wax, rounded like a slender taper of the length of your little finger, but slightly thicker at the top. This wax is called the gate and you should “solder” it on with a hot iron. Then take some vigorously kneaded clay and carefully cover each handle separately, so that all the holes of the carving are filled. When the handles are dry, carefully cover them again all over except for the top of the gate; and so the same a third time.
Afterwards put these molds near the coals and when they are heated, pour out the wax. After it has been poured out, put the molds right into the fire, turning downwards the holes through which the wax came out, and leave them until they are red-hot like the coals. Immediately melt the silver and add to it a little Spanish brass, for example, a weight of two pennyweight if there is half a mark of silver, and in proportion if there is more or less. Take the molds away from the fire, stand them up firmly, and pour in the silver in the same place from which you poured out the wax. When they are cold, take away the clay and with a file and gravers fit the handles to the bowl.
Using this process each casting is unique. The metalsmith builds each object working with prepared beeswax that can be carved and moulded to create fine detailed patterns, knowing that the resultant shape and surface texture will be reproduced in the metal. The wax is then covered in a thin coat of fine clay that will take an exact impression of the wax model. Additional layers are built around the first layer and, when dry, this composite mould is heated over a furnace causing the wax model to melt from the mould and leave an interior void for the molten metal. The mould is then placed in the furnace until red hot. The prepared metal is separately heated in a clay crucible to an approximate temperature of 1150˚C and then poured into the mould, filling the void caused by the melted wax model. When cool, the mould is broken open and the casting removed for final finishing using chisels, files and burnishers.
Text and photography:Kevin O'Dwyer
Lost Wax Casting