When I write about creating jewelry, one of the steps I always mention is casting. But what is casting? Put simply, it’s a process by which jewelry models are made into metal.
These days, I send my pieces off to a professional casting company, another family-run business like my own. But I’ve certainly made many castings in my day, thanks to my excellent education at SCAD. Lost-wax casting, the most common casting method, has been around since the days of the ancient Egyptians. As they say, “If it ain’t broke, don’t fix it!”
Here’s how it works:
Wax Models and Sprues
The first step in creating a piece of metal jewelry is to create a wax model, an exact replica of the piece. There are two main ways that I make waxes. I either 3D print them from a CAD program (the ancient Egyptians did not have this option!) or create a reusable mold from a metal master that can be injected to get a wax. My collection pieces all have molds from metal masters to cast over and over.
Once formed, the wax models are attached to something called a sprue, almost like a branch on a little tree. Each of these branches will become a tube through which the molten metal will flow. But we’ll get there. Several sprues can be attached to a single base, so it looks like a wax tree sprouting tons of little jewelry designs. Very fun!
The little wax “tree” is then placed inside a metal container.
Plaster Investment
Next, we mix up a heat-resistant plaster called the investment. This investment is poured inside the metal flask to completely cover and surround the wax model. The only bit of wax that will be seen is a little opening at the bottom, called the button. This would be the base of the tree trunk. Once poured, we let the investment harden and become solid.
Burn Out
After the plaster has hardened, it’s time to place it in the kiln. Over 10-12 hours, the heat in the kiln is gradually turned up, in a process called burnout. The heat-resistant investment stays in place, but the wax model completely melts away through the open hole in the bottom. Over time, the entire wax model is lost. (Hence, “lost-wax” casting.) In its place, there is a hollow space or void in the center of the investment, the exact inverse of the model. So cool!
Pouring Molten Metal
The next step is to pour the molten metal into the void where the wax used to be. The metal is melted in a crucible using a super-hot torch. (I think it’s pretty clear why I can’t do this in my studio!) Then, the molten metal has to be moved into the void left by the melted wax.
This can be done in several ways, but many casting houses use centrifugal casting, where the crucible full of molten metal is placed on one side of a centrifuge, and the plaster flask on the other. The force of the spinning centrifuge forces the molten metal into the mold.
After the molten metal is poured, the circular button (the only visible part) will be red-hot and glowing.
Quenching
Once the metal inside the mold has cooled down a bit, the entire thing is quenched or plunged into a bucket of cool water. Finally, the plaster casing will break apart and be destroyed, leaving only the solid metal.
This metal casting will look exactly like the original wax model. That is, it will resemble a tiny tree with lots of little pieces of jewelry protruding from the branches, like a spiky porcupine!
Cutting and Cleaning
The final step in the casting process is to snip, saw, and file each piece of jewelry free from the sprue tree. This is done with a variety of hand tools. Then, the pieces are sanded down to remove any trace of the sprue to which they were originally attached.
These initial cast pieces are very rough and require a great deal of care to get them to the beautiful place that we recognize as fine jewelry. This is all the work that takes place in my studio and makes up the bulk of the jewelry-making process. But none of that magic can happen without casting!
Of all the ways to go from the original model to the final product, I bet you never imagined this! Lost-wax casting is truly one of the most fascinating aspects of the jewelry industry.
Keep following this blog for more jewelry-making secrets!
