Lost Wax Casting - How we Do It
Hi, I am Marcia. I thought you would like to understand a bit better what is involved into some of the work you see at our shop. Depending on what I want to achieve, I will build the piece layer by layer by welding a sterling silver sheet or coil. However, when I need a higher volume, this method is not enough to create what I have in mind. That's when I chose to sculpt the piece and cast. When you see on my work a tri-dimensional feel, it was undoubtedly done through lost wax casting.
Lost wax casting is a fascinating process that dates from 4500–3500 BC. Although some of the tools changed throughout the centuries, the basis of the technic is pretty much the same.
Our silversmith casting is done in-house. Its just Fred and I and lots of excitement with a process that never gets old. The cast is when you get to see in silver a lengthy project come to life.
I start with pendant, a pendant, a ring, or earrings frequently sculpted wax. On this finished wax piece, I attach another wax part called spur that looks like a wax stick. The spur is connected to a rubber cap that tightly fits one end of a metal tube called flask. After attaching the wax on the inner part of the rubber cap, the rubber cap is placed at one end of the metal flask.
Time for the next stage, the investment! Investment looks like plaster of Paris. Once mixed with water it hardens (fast!). In this step, you combine the investment with a precise quantity of water. Mix it well and pour into the flask. This simple operation between preparing the investment and pouring is anything but simply because any air bubble stuck inside can ruin your final caste piece!
When the investment dries, in about 2 hours, the rubber cap is removed from the metal flask and voila! We now have the metal flask wholly filled in one end. The opposite side of the investment filled flask shows the end of the wax spur. After the wax is removed, this part will become an empty tube making a passage for the molted silver to reach the original wax piece in the flak.
Here begins another step in the casting process. At this point, all wax must be removed. Basically, the waxwork that took hours to sculpt is about to melt! That’s the beauty of the process. After eliminating all wax residue, we end up with the metal flask, filled with investment, except for the section where you wax piece was standing.
Melting wax needs heat. This is done by placing the metal flask in a kiln until the temperature is high enough to do the job. We have been very successful by letting the temperature rise to 1000F. To avoid filling the studio with melted wax vapor, we always steam the flasks for about 3 hours before placing them in the kiln. This extra step eliminates a large quantity of the wax inside the flask.
Here at the studio, we usually burn the wax, turn the kiln off, and keep the flasks stored in the kiln until casting time. When we are ready to cast, we turn the kiln on until it reaches about 940 F. Now we are ready to cast!
We use a centrifugal casting machine for all our jewelry castings. The silver grain, previously weighted for each flask is placed into the centrifugal arm crucible. Heat is applied to melt the metal. When the metal is completed melted, the flask is carefully taken off the kiln and placed on the flask slot at the centrifugal arm. The arm tension is released, and the arm spins, shooting the molted silver through the investment hole into the flask.
After the metal hardens, the flask is placed in a bucket of water. The investment disintegrates, and cast piece is free.
Time for the bench work. After casting, the pieces look anything but pretty. A lot of cleaning, filing, and sanding takes place after casting.