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Lost wax casting is an ancient art. The technique was first employed by the early Egyptians but it was also independently discovered and used tribal artists in South America who used it to cast pre-Columbian gold. It was rediscovered by the great Renaissance goldsmith Benvenuto Cellini. While modern versions of the lost wax process employee a few differences, such as industrial vacuums to pull the molten gold down into the mould, the lost wax method as used today is really very similar to that employed by the goldsmiths of Egypt and the pre-Columbian tribes.

The Lost wax method is practical for casting both gold and silver alloys. Although it is most commonly used for rings and bracelets, the lost wax process can be used for casting a variety of objects. This method is currently used to create about 60% of all karat gold jewelry, as well as a significant part of all silver jewelry, enabling manufacturers to produce pieces in multiple numbers at a favourable production cost. The lost wax method allows jewellery artists to copy the finest detail into a gold casting. The jewellery produced by casting can also be subject to further treatment by soldering on additional items, etc. The modern version of the lost wax casting process can be described as follows:

1) From an original design, a model is made in metal or resin. A rubber mould is then made from the model.

2) From this rubber mould multiple copies are made in wax. The wax copies are attached together by a connecting sprue. A group of wax copies are attached together to form what is called a tree.

3) The tree is then placed in a metal flask and covered with plaster of Paris. Once it hardens, the plaster mold is then heated in an oven. The wax melts and is lost, leaving a hollow plaster mold.

4) Molten gold is then poured into the mold as the entire mold is placed in a vacuum the vacuum action draws the gold down into every crevice of the mould forming a perfect copy of the original design.

5) The plaster is then broken and washed away from the now cooled gold casting. The individual gold items are now ready to be cut from the treaty for hand finishing and polishing.

Now if the ancient and primitive peoples of Egypt and South America could do lost wax casting, and produce beautiful works of art, then so can you - with the proper tools and training. Most of the necessary tools and equipment can be purchased right over the internet, and books are available to teach you what you need to know. Here are the basics of how you can do your own lost wax casting using the pressure of steam.

1) Gold, Silver or other precious metals in a clean and castable form (often used jewellery needs cleaning and melting with borax to remove dirt, corrosion and impurities).

2) A torch powerful enough to melt a few ounces of gold or silver.

3) Lost wax casting investment material (the plaster like stuff).

4) A rubber mixing bowl - it is important to mix your investment material with as few bubbles as possible. The bubbles tend to adhere to the wax model and create bubble bumps on the finished product. Shake or vacuum the material to remove bubbles.

5) Various wax models and extra wax to make access sprues. The jewelry wax material is a special type, not just normal paraffin as is used in candles. It has a known density so that the correct amount of metal can be melted for the casting process.

6) A burn out oven capable of about 800 F, which is used to vaporize the waxes.

7) A "crucible" which in this case is a metal tube, to contain the investment and wax for the whole casting process.

8) A steam generator - usually a metal can which has wet material attached to the inside.

After the wax is made, the sprue attached, the investment poured, and the entire product baked to drive out the wax, molten metal is poured in and the steam unit pressed on top. Steam thus created pushes the metal down into the mold. After a time is waited for the metal to cool and solidify, the casting is put under water and the investment material dissolves away.

As a note, casting molten metal can be very dangerous. Molten metal splattered on clothing or skin quickly causes severe burns. Protection of the eyes and other parts of the body is necessary. Wax vapours can be flammable so precautions need to be taken there as well so that the room is fully ventilated. It is strongly urged that anyone who would like to attempt this process purchase books that provide more detail as to how this casting process is done, and read them carefully.

 

Article Author: Chris Ralph

Chris Ralph writes on small scale mining and prospecting for the ICMJ Mining Journal. He has a degree in Mining Engineering from the Mackay School of Mines in Reno, and has worked for precious metal mining companies conducting both surface and underground operations. After working in the mining industry, he has continued his interest in mining as an individual prospector.

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