The lost wax method is the simplest way to make a mold for gold jewelry. You do not need expensive equipment and what you do need is readily available at hardware, craft, hobby and art supply stores. The lost wax method is perfect for jewelry because it captures so much of the fine detail.
Make a model of your gold jewelry piece by carving it in wax. Jewelers wax is the best, but you can melt down a candle as well. It is a good idea to trace an outline onto the wax first, then carve it out with an artist's knife.
Use a rubber mold to make the model instead of carving. Just press the wax into the mold and when you remove the model, it will have the imprint of your design in the wax in minute detail. Rubber molds are available at art supply stores.
Attach a sprue, which is a solid piece of wax that you make in the form for a funnel and attach to the mold. When the wax is melted, it will leave a hole for you to pour the liquid gold into the mold. You need to put one on the bottom as well to let the air and gases out, otherwise you will end up with a bubble and the metal will not go all the way into the mold.
Set the wax in plaster. There are two ways to do this, depending on how you are going to heat the mold. If you are going to use a kiln, you need to put the model on a sprue base and put a special metal flask, which will fit into a groove in the sprue base, around the model. Then the flask is filled with refractory plaster. The home crafter can use a product called faster plaster, which will allow you to use a microwave instead of a kiln. Put the model into a cup. Styrofoam is just fine. Pour in the faster plaster, let it set for an hour. When it is set, remove the styrofoam. Put paper towels in the microwave and put the now solid plaster in upside down but resting on pieces of wood so it does not touch the paper towels. The heat of the microwave or kiln will melt the wax and the sprue, leaving you a hollow plaster mold that will have a perfect imprint of your design on the inside.
When you do not see any more wax coming out, remove the mold from the microwave or kiln and let it cool completely. Then lightly tap to make sure there are no bubbles and you have your mold ready to pour in the liquid gold.