Casting is one method of creating jewelry pieces that can be replicated several times as opposed to cutting, bending and welding sections of metal. Lost wax casting is one of several methods of casting jewelry. Even with a meticulously designed jewelry piece, the casting may turn up with some imperfections such as bumps that can ruin the final piece. When this occurs the casting needs to be cleaned first. The lost wax casting method is suitable for gold and silver casting and is used in about sixty percent of all karat gold jewelry. To clean jewelry castings, take a look at the steps below.
- First let us understand how a casting is made. After the final model of the jewelry design has been replicated in rubber, this will be injected with liquid wax that will be the final pattern for the casting. The wax pattern is attached to a wax pole called a sprue. The sprue is a rod coated with hard wax. This is where the molten metal will be poured once the casting begins. Several completed wax patterns attached with sprue will be assembled to form a tree. The tree will create the void where the molten metal will be injected to cast the final jewelry. The tree will them be placed on a rubber base and surrounded with a cylindrical metal flask. Slurry made from plaster-like substance, called investment will be poured into the cylindrical flask to coat the tree leaving the sprue ends exposed. Once hardened the flask is removed from the rubber base and placed in an oven with controlled heating to melt the wax. The resulting hollow void will then be filled with molten metal through the sprue openings and allowed to cool and harden. The investment is then dunked in water to be washed away from the casted metal.
- The next step is cleaning the jewelry casting. First thing you need to do is to remove the sprue. You can do this by using a jewelry saw and cutting as close to the jewelry design as possible. You can remove the rest of the sprue through different polishing techniques. You can grind what remains of the sprue using fine carborundum bits. Grind the sprue as close to the pattern until it is no longer noticeable. Make sure that you do not touch the design itself while you are doing this.
- You will notice that there may be some oxidation that coats the surface of the metal. This is caused by the heat during the melting process to remove the wax from the plaster cast. This can be removed by placing the jewelry piece in a pickle solution – an acid bath that can be heated in a hot pot set on low. Wash the jewelry in running water as soon as the oxidation and the rest of the investment has been removed.
- Select the right type of abrasive metal brushes that can be attached to a flex shaft, Dremel or a buffing machine to remove burrs and other imperfections on the surface of the jewelry. You can also use small metal files and pumice to make the surface smooth. Choose the best applicable tool to clean and make the jewelry surface as smooth as possible.
- Place the jewelry piece in tumbler with stainless steel shot to burnish it. Check the piece if the surface is already smooth and any nicks, indentations and bumps have been removed.
- Polish the jewelry on the polishing wheel. There are three steps involved in the gradual polishing process. First step is to use bobbing paste for a quick polish to remove surface burrs that have been left out, followed by using Tripoli paste which is still abrasive but finer than the bobbing compound. Finish the polishing process with rouge. It comes in different colors. Use the one that is suitable for gold or silver jewelry.
Be thorough when cleaning jewelry casting. Inspect the piece all around. Use a magnifying glass to see minute imperfections. Wear protective gear when working with metals, cutting and polishing devices and polishing compounds Metal dust is quite heavy and is harmful when inhaled.