Lesson: Mold Making

Lesson 2: Mold Making
Mold Overview
Molds can be used to create multiple casting of one original piece. There are several types of molds. Most industry made jewelry molds are vulcanized rubber molds. Rubber is put under both heat and pressure until it hardens, yet retains its flexibility. This process helps increase the life of the mold. Vulcanized rubber molds last a long time. However, these molds are unsuitable for molding anything that cannot take heat or pressure.
For molding items that are heat or pressure sensitive, RTV (room temperature vulcanizing) molds are the best option. RTV molds can be either silicone or polyurethane plastic. Depending on the mold material, these also have a long life, and require less equipment to produce. Alginate and brushable latex can also be used to create molds.
Standard molds are comprised of 2 halves. The halves fit into each other snugly with out movement. Brass “buttons” can be used to register the halves, or tabs cut into the mold. These are called “closed” or 2-part molds.
Depending on the original, you can also make an “open” or 1 part mold. These molds are easier to produce since they don’t require cutting or separating the mold, but can only be used on pieces that doesn’t have a lot of undercutting.
In order to create multiples of a piece, the mold is injected with molten wax, creating a wax version of the piece. Multiple waxes are created, and then each wax is cast.
A wax injector is used to shoot the wax into the mold. Simply pouring the wax into the mold will not get a full impression of the piece. The wax cools too quickly for that. By using compressed air to get force behind the wax as it comes out of the injector, you can be assured of complete waxes.
Open molds can be filled by pouring wax into them.
Both molds can be used for casting other materials than wax.

RTV Molds:
• Read the instructions for the compounds. RTV Molds are usually comprised of a Part A and a Part B (activator or catalyst). You need to check to see whether the molds need to be vacuumed during mixing and what the mixing ratio is.
• Make sure that your mold frame is clean, and spray with mold release.
• If making an injector mold, attach sprue and funnel to original.
• Spray original with mold release.
• Arrange original in the mold frame. Check that orginal is placed so that it is only touching the frame at the designated opening.
• Mix mold compound. Wear gloves. Measure very carefully and stir completely and thoroughly.
• Pour compound smoothly, slowly, and evenly into frame.
• Let mold cure.
• Once cured, remove mold from frame. Thin flexible spatulas can assist in this.
• If a 2 part mold, separate and cut apart.
• Trim any excess from the mold.
• Your RTV mold is ready to use!