Metal casting is a project that anyone can do at home, if the right equipment is available. The "lost wax" casting method is the easiest. The process gets its name from the way wax melts away to make the mould. A wax replica of the finished ring or pendant heats until it burns out, leaving a moulded impression behind used to cast a silver ring or pendant. Use caution when casting any metal, as you are working with very hot and very fast-moving equipment.
Carve your piece out of wax, using the craft knife. Ring stock is a tubular piece of wax that jewellers use. Carve out the appropriate size first, then work on your design. This may take time, patience and several wax pieces to achieve the type of detail you are looking for. The wax piece made during this step must be the exact copy of the piece of silver jewellery that you intend as your finished product.
Use a wax pin (long, thin heated piece of wax) to attach the mould to the sprue in the bottom of the rubber base. Fit the flask into the sprue base. Mix the investment, which is a plaster-like material, according to the package instructions and pour into the flask, covering the mould completely. Let it sit overnight to harden.
Take off the base and fire the mould in a kiln. Do not use the oven, as there are toxic fumes created when heating. Heat the kiln gradually to 649 degrees Celsius. The mould will disappear or "burn out" into the investment, leaving a perfect impression behind. Let the flask cool completely before going on to the next step.
Prepare your centrifugal jewellery-casting machine according to instructions. Balance and wind it before beginning. Insert the cradle-shaped crucible. Use the welding torch to heat the crucible by placing it over the top with the flame inside the cradle. Prepare it with boric acid. A small amount of boric acid (about 1/2 tsp) will make a glassy coating on the inside of the crucible to keep the silver clean and free of contaminants. Keep the torch flame inside the cradle.
Add your silver pieces to the crucible. Test the silver before using to ensure it is free of contaminants such as plating. Add casting grain according to the instructions. Continue to heat the crucible. Do not put the flame directly on the silver. Instead, move the flame around the silver inside of the crucible. Direct flame will boil the silver, causing holes in the final product. Use a graphite stick to stir the silver if needed.
Lock the flask in place and release the centrifuge. The liquid metal will now shoot from the crucible and into the flask to fill the mould. Allow the centrifuge to spin to a stop. Using heavy metal tongs, take the flask out of the centrifuge and into a bucket of water. Roll around until the water stops bubbling and the flask is cooled.
Take the white investment off the bottom of the cooled flask. Your silver piece of jewellery will be attached. It will also have the sprue attached. Use a small brush or old toothbrush and the bucket of water to thoroughly clean off the investment. Clip off the sprue with metal shears and polish.
Things you need
- Craft knife
- Wax mould
- Metal flask with rubber sprue base
- Investment (white powder)
- Centrifugal jewellery casting machine
- Sterling Silver
- Welding torch
- Boric acid
- Casting grain
- Graphite stick
- Bucket of water
- Metal tongs
- Small brush or old tooth brush