Silver casting requires a mould that can withstand extremely high temperatures. Unlike soft metals, such as pewter, tin and lead, silver will melt only once it is heated to 965 degrees Celsius (1,763 degrees Fahrenheit). To create a mould that can withstand this temperature, use refractory plaster and a wax model of your piece. With these, you can make a mould using the lost wax technique. In this process, you create a mould around your wax model and then heat it until the model melts, leaving a hole in the shape of your object that is ready for casting.
Sculpt a model of your piece out of wax. To do so, knead the wax in your hands until it becomes warm and pliable. Sculpt fine details using tools meant for pottery. Once you are finished, create a 5 by 0.6 cm (2 by 1/4-inch) tube of wax and affix it to one end of your model.
Put your wax model in a metal bucket and put the bucket on a stove burner. Balance your model on the tube of wax so that it is suspended in the air. Turn the burner on, setting it on low, and let the wax touching the bucket floor melt and adhere to the bucket. Turn the burner off immediately once you observe this and remove the bucket to cool.
Paint liquid wax all over the inside of the bucket using a large paintbrush. The liquid wax will keep your mould from sticking to the metal of the bucket, allowing for easy removal.
Put on your respirator. Take a second bucket and put it in your sink. Open your bag of refractory plaster powder and pour it into the second bucket. Pour enough to cover the wax model. Turn on the faucet, allowing water into the bucket and stirring the plaster with a stirring rod. Turn the water off when the plaster achieves the consistency of heavy mud.
Pour the plaster slowly into the bucket with your model in it. Do not pour it directly on your model or you will risk breaking it. Instead, pour around the edges of the bucket. Completely cover your model with plaster, then add another inch of it. Let the plaster cure for one week.
Tap the bottom of your bucket gently with a hammer to loosen your mould and slide it out of the bucket.
Put your oven rack down as far as you can and put your mould on top of it, with the wax tube pointing down. Put a metal pie tray under your mould to catch the wax that will dribble out of it.
Set the oven to 71 degrees C and wait for 15 minutes before checking on your mould. As the mould heats up, the wax will melt and pour down onto the pie tin. Turn the oven off only when you see that no more wax dribbles out. Let the mould cool for three hours.
If you are a novice, do not attempt to cast silver without skilled supervision.