Lost Wax Casting
After a wax carving is completed, it is put on a sprue (wax rod) which is attached to a rubber base. If several pieces are to be cast in the same metal, they are put together to form a tree. The sprued wax is then put into a metal flask that is filled with an investment material which is similar to plaster of paris. The investment has been put through a vacuum process to remove any air bubbles. After the investment hardens, the rubber base is removed and it is placed into the oven. It then “bakes” at a series of high temperatures (up to 1575 degrees F) for eight to ten hours, causing the wax to vaporize, or get “lost.”
The exact impression of the original wax is left in the investment material, which is then removed from the oven and placed into a centrifugal casting machine with a crucible attached to one end. A mathematical formula allows us to translate the wax eight to gold weight, so that we can measure the proper amount of casting grain (small gold nuggets).
The metal is placed in the crucible and melted with a torch until molten. The wheel is released, causing the contents to spin at high speed. This forces the gold into the investment, where it solidifies in the exact shape as the cavity.
After a brief cooling period, the flask is removed and quenched in water, causing the investment to disintegrate. The piece of raw gold casting is then cut from the sprue in preparation for clean-up and polishing.
The entire process is done in-house here at Urban Jewelers, which allows us to maintain our high quality standards and improve turn-around time.