How to Make a Mold for Glass Casting

Step-by-step simple plaster/silica mold for casting glass. This video demonstrates making an open-face mold around an oil-based clay sculpture. After the mold-mix has hardened, the clay is removed, leaving a negative impression of the sculpture. Glass will then be loaded into the mold and placed in a casting kiln which will slowly heat the mold, causing the glass to melt into the cavity. This is a one-off casting process because the clay is often damaged or destroyed when removed from the mold. However, this is a very fast way to transform a clay sculpture into glass.

The mold mix used here is 1 part Plaster, 1 part Silica Flour (300 mesh) and 1 part Water.

The dry materials are mixed dry and then added to the water. They are allowed to soak for 3 minutes (until all the dry has absorbed water) and then they are mixed by hand for 2 minutes. A face coat is then added with a brush, taking care to push mold mix into all the details and crevices to prevent bubbles. As this is happening the mold mix is setting up, thickening to a whip-cream like consistency. When it is significantly thickened it can be applied to the clay and will hold to vertical surfaces. If the mix is still too wet it will run down the sides and puddle out. This just means you should wait a bit longer before applying the mix.

Ideal mold wall thickness for small castings like this is roughly 2—2.5 inches. The goal is to make even walls all the way around the clay. Even molds dry and cure evenly, preventing cracks which can cause the mold to fail at casting temperature, allowing the glass to leak out! For most sculptures hand-build molds like this are stronger, because they can more easily be made uniform as opposed to poured, block molds.

SAFETY NOTICE! This mold mix contains crystalline silica, which is a known health hazard. Proper dust masks or respirators are essential when working with this material in dry form. N95 masks or filters are recommended.

Видео How to Make a Mold for Glass Casting канала Kent State Glass