by Ray Wilson
History of casting
Investment casting dates back thousands of years. Its earliest use was for idols, ornaments and jewellery, using natural beeswax for patterns, clay for the moulds and manually-operated bellows for stoking furnaces. Examples have been found around the world: from Mexico to Mesopotamia, and Egypt to Africa where the investment casting process produced detailed artwork of copper, bronze and gold. The earliest known text that describes the investment casting process (Schedula Diversarum Artium) was written around 1100 A.D. by Theophilus Presbyter.
Navajo Indians used tufa stone to create impressions in the soft stone and then pour in molten silver in the early 1800s.
History of Casting in NBLC
The first lost wax casting was introduced into NBLC by Ross Chapman about 20 years ago. Initially Ross used a car tyre pump in a home built apparatus to “suck” the molten metal into a mold. As members became more interested, the club invested in better equipment. A computer controlled kiln and centrifuge were purchased, with Ross building a shroud around the centrifuge using a stainless steel drum from a washing machine drier.
Ed Hindmarsh built 2 vibrating tables and donated to the club to assist with removing air bubbles from the investment.
Tom Power then built and donated a vacuum table so that the air was removed from the investment, giving better quality results.
Over the years we have continued to improve the process where we now have over 90% success with castings; a very good result considering how many touchpoints there are where members have been involved in the process. From weighing the waxes, to spruing correctly, to vibrating the investment to providing the correct weight of metal, to ensuring the torch flame is a neutral flame, to ensuring the metal is completely molten; all of these areas can and do cause problems with the outcome. Some clubs as part of their casting process sprue all of the required models into one flask. This is all controlled by one experienced member. NBLC has retained investing individual flasks; exactly as Ross started us off. This means individual members have more control and more involvement in the casting process, but it also means that the requirement for volunteers to assist in the process is more intensive. It is a credit to all of our members who participate in the casting workshops, so that other members enjoy an interesting sideline to the hobby of lapidary.
In the last 10 years, we have also conducted cuttlebone and broomstick casting with members leading these new endeavours.
Sand casting has also been conducted by Kirra-Lea Jewellery on a contract basis for members.
Varieties of casting
Lost Wax Casting is as the name suggests. A wax model of an object is placed in a steel flask with a plaster mix poured in to fill the flask. The flask is then “burnt out” over several hours so that the wax vaporises and leaves an empty void where the object was. Metal is then melted and induced into the void in the flask using either vacuum or centrifugal force. At NBLC we have continued to use a centrifuge on the back of the good results we achieve. The wax object can either be carved from wax rolls or sheets or by purchasing commercially available models of rings and pendants.
Organic material like flowers and gum nuts or seed pods can also be cast using this process. As long as the object can burnout at under 700 degrees Centigrade and can hold its shape under the weight of the investment mix then it can be cast in metal.
Further research: NBLC has several books in the library that specialise in lost wax casting. Murray Bovin’s Centrifugal Or Lost Wax Casting is an excellent guide for anyone who wishes to learn more about this process
Commercial waxes cast using Lost Wax Method
Commercial ring casting in Sterling Silver
Sand casting is a process where a special type of very fine grained sand is pushed under pressure into a frame and then the object you wish to cast is pushed into the sand to make an impression. Once the object is removed, the 2 halves of the frame are locked together and molten metal is poured into the frame to create a copy of the object.
Further research: https://www.KirraleaJewellery.com is the web page of Kirra-Lea who has conducted sand casting lessons at NBLC.
Craig Dabler is an American who specialises in sand casting equipment and supplying sand to hobby casters. Craig has several videos on You tube that go through the sand casting process. https://www.youtube.com/watch?v=wlzb_9KhEQw.
He also sells kits and tools at:https://www.diycastings.com/
Sand Casting Frame
Red Sand for Sand Casting
Cuttlebone is the internal shell of a squid like mollusc called a cuttlefish. The shell is made of Aragonite, a form of calcium carbonate, that is soft enough to push an object into to make an impression or objects can be carved using simple tools. Cuttlebone casting has been in use throughout the Mediterranean countries since at least the 16th century. Similar to sand casting a mold is made using 2 pieces of cuttlebone, where a shape or object is impressed or carved, the 2 pieces are bound tightly together and then molten metal is poured into the mold. The beauty of cuttlebone casting is that every piece is unique depending on the shape of the ribs within the cuttlebone. It is also a reasonably easy process to undertake without the expense of kilns and centrifuge like lost wax casting.
Further research: Tony deLuca is an authority in cuttlebone casting and has taught classes in cuttlebone casting for over 30 years in Ontario. Tony has several short videos on his web page demonstrating cuttlebone casting. If you are interested in cuttlebone casting these are worth warching at:
Cuttlebone Casting - pendants
Broomstick casting is a technique used to create unique forms. Millet straw from a straw broom is bundled tightly together and then molten metal is poured down the top of the bundle. The molten metal shape is formed by the metal running down and around the straw. The shapes are unpredictable and unrepeatable which can provide an interesting organic piece of wearable jewellery. However unlike cuttlebone or lost wax casting, you can reuse the broomsticks – just clean out the metal and re-bundle and tie tightly ready to cast again.
Broom Casting with bezel set stone
Casting in Jewellery
Casting has a wide range of use in jewellery; specifically, commercial jewellery is predominantly cast, as the cost is significantly reduced compared to hand manufacture. For the hobbyist though, casting can be used to supplement hand made pieces by adding texture or contrast. Cut gems can be added to cast pieces to add colour to the cast item.
Casting of stones in place is used in some circumstances. The rule used to be red,.blue green are suitable stones, meaning ruby, sapphire, emerald. Now cubic zirconia is also used. Other stones like zircon or topaz are not suitable and will not withstand the heating of the casting process.
Sterling silver ring - commercial wax set with sapphire
Gold ring, hand carved - set with sapphire
Cuttlebone used as components in jewellery
Broom casting as component in jewellery