How to Do Jewelry Casting

There are several ways to manufacture jewelry, but one of the more common techniques for producing intricate patterns in silver and gold is the casting process. First making a wax model, it is used to make a mold into which the molten metal is poured and cools to take the shape of the designed piece of jewelry.

Difficulty: Moderate

Instructions

Things You'll Need:

• Modeling wax Wax carving tools Silicon mold rubber Investment mold compound Investment casting oven Mold flask Crucible Precious metals Finishing tools

Design and Create a Model

1. Plan the piece of jewelry. Design the piece before ever carving into the modeling wax. The goal is to determine the starting size of the wax piece which will eventually become the model for the piece of jewelry.

2. Carve the piece in wax. Using the wax carving tools, take a piece of modeling wax bigger than the finished piece and carve out the design. Mistakes made here can be corrected, as modeling wax is typically reusable, by melting and casting it back into basic shapes. Master jewelry casters typically keep a collection of basic shape molds to create their first wax pieces.

3. Add sprue pieces of wax to the designed piece; these are short rods and wedge-shaped pieces that provide a path for the molten metal to enter the mold, and the air to escape. A small torch or lighter will soften the wax sprue enough to bond to the piece, typically in a relatively plain spot, such as the inner surface of a ring, or where attachment hardware will later be soldered.

Make the Negative Rubber Mold

4. Use RTV silicone rubber, if you plan to make a number of copies of the design (such as if the design is a basic shape for later designs or if it is a production piece).

5. Mix the rubber according to the manufacturer's instructions, then, pour it into the mold flask, around the jewelry model. Be certain to leave the sprue pieces exposed.

6. Cut the mold to form a two-part mold. This mold cannot withstand molten metal temperatures, but can withstand the temperature of molten wax, enabling many reproductions of the design to made in wax for the next step.

Make the Investment Cast

7. This process is similar to the rubber step, only the investment material can withstand molten metal temperatures.

8. Secure the wax model in the mold flask.

9. Fill the container with investment material to surround the was mold, again leaving the sprue pieces exposed. Allow the investment material to solidify.

10. Heat the mold in an investment casting oven, which is designed to melt the wax out and collect it for reuse. What remains is the ready-to-use mold.

Cast the Piece

11. Melt the precious metal in a crucible designed to provide the right temperature. (See Tips for some important information on temperatures.)

12. Carefully pour molten precious metal into the mold. Proceed slowly and surely, making sure that you stop when the metal completely fills the mold.

13. Remove the container surrounding the investment mold. Gently break apart the mold, leaving the piece of Jewelry with sprue pieces attached. You may regrind and reuse some kinds of investment material.

Finish the Piece

14. Cut off the sprue pieces, and save them for reuse.

15. Use carvers, files and polishing tools to provide a clean finish to the piece of jewelry.

16. Add any precious stones, chains or attachment hardware.

Tips & Warnings

• It will take several times to get the first couple of designs right. The beauty of this technique is that since just about everything is reusable, if the first attempt is a failure, melt it all down and try again. Be sure that for the melt and pour that your work surfaces can withstand upwards of 2000 degrees Fahrenheit and that if a spill occurs, you can safely avoid the molten metal, while placing the crucible back safely down and retreating until the metal cools. Typically, since it costs a good deal of energy to melt the metal, many molds are made before hand, so that one pour can create a number of pieces.
• Silver and gold have melting points that can approach well over 1500 degrees Fahrenheit. Extreme caution is recommended during the metal melting and pour stages, as these temperatures will destroy flesh. Do not attempt to use liquids or other cold agents to speed up the cooling of the piece, as an explosion of steam could occur sending molten metal everywhere, including towards you.

References

• Creative Casting: Jewelry, Silverware, Sculpture; Sharr Choate; 2007