What is “lost-wax” jewelry casting?
Lost-wax casting is actually the most common way that metalsmiths make jewelry. The process starts with the jeweler carving and sculpting a piece of wax to look like the piece of jewelry they want to make. Wax can be bought in a variety of shapes and hardnesses, and can be easily carved and shaped by hand or with simple tools. Once the model is ready, you attach thin wax rods called sprues to the piece at various points. The sprues will act as channels to let the wax flow out and the metal enter the model.
Next, you place the model with its sprues attached to a point at the bottom of a steel flask (these flasks look like a 3″ slice of large pipe). The flask is then filled with plaster investment that hardens around the model and its sprues. Using a kiln, the flask is fired for several hours so that the wax model and sprue rods melt and leave the flask. This step leaves you with a plaster cast of the item you are trying to make. It has a hollow form inside that is the inverse of your model. To turn the model into metal, you use a centrifugal or vacuum casting machine to shoot a jet of molten metal quickly into the void in the flask. The metal flows along the sprues and fills the space left by your wax model. Once the flask is somewhat cool, you dissolve out the investment, cut your piece off of its sprues, and clean up the rough parts. You now have a metal version of the wax model you created.
Most jewelers who cast items make a permanent mold of their wax model that they can reuse as often as they like. They can inject molten wax into this model to recast hundreds (or hundreds of thousands) of the same item. The cost of actually manufacturing any one item therefore goes way down. That and foreign labor is why you can buy jewelry in department stores for practically the cost of the raw metal.