How can I Release Glass Trapped in Casting Moulds?

How to get stuck glass out of a reusable mould?

The material is important to the method of removing stuck glass.

• Metal expands and contracts more than glass.

• Ceramic expands and contracts less than glass.

Mechanical methods

• Metal moulds can be hit relatively hard to break the contact between the mould and glass.

• Ceramic moulds should have only gentle taps, as they are more fragile than metal.

• If the glass is stuck, but moveable within the mould. It may be possible to wiggle the glass and mould against each other, which after a time may wear away the contact points and release the glass.

• Do not try to pry the glass from the mould. It is likely one or the other will break.

• Destructive method is to break the mould or the glass, which ever is the least important.

Contrasting temperature methods

Drape over metal –

• The metal contracts more than the glass, so placing the two in the freezer is one possible approach.

• Alternatively, heat the glass with hot water

• A third method is to place the drape upside down in the kiln and take it up to slumping temperature. Peek to determine when the glass has relaxed enough to be free from the mould. If the release temperature is above the annealing point, anneal again as before.

Drape over ceramic -

• The glass contracts more than the ceramic, so heating the glass with hot water may provide enough expansion to release from the mould.

• Or place the drape upside down in the kiln and take it up toward the slumping temperature. Peek to determine when the glass is released and skip to the anneal and cool process.

Slump into metal -

• The metal contracts more than the metal, so heat treatments will work best.

• Apply hot water to the metal until the glass is freed.

• Place the mould upside down on short posts and fire until the glass drops out. If the annealing temperature is exceeded, anneal again.

• Bang the metal mould with a rubber mallet. This risks breaking the glass, of course.

• Freezing only tightens the hold of the metal to the glass.

Slump into ceramic -

• The glass contracts more than the ceramic, so cold can work.

• Usually, glass sticking to a ceramic mould is a result of insufficient coverage of the mould with the separator.

• Placing the mould and glass in the freezer for a few hours may allow the glass to contract enough to be freed when taken out.

• Place the mould upside down supported on short posts. Set the firing to go to fusing temperature. Monitor with quick peeks from the slump temperature at regular intervals. When it drops, skip to the anneal process.

• Firing to a high temperature does not always release all of the glass.

Using adequate and appropriate separators to avoid trapping the mould or the glass need to be used to prevent the need to employ these release methods.