Casting Glass

Step 6: Kiln cast glass

Now you need a furnace big enough to hold your investment in the flask and your glass piece over it. We simply upended the crucibles full of glass over the mouth of the investment.

Close furnace and turn the heat up to 800C.
Leave it in there for six days.

We also put some little ceramic boats with extra glass chunks in the furnace, just so that we'd have some visual feedback.

(We did 900C for 12 hours, but our glass didn't turn out very pretty. The six-day figure is from this source: http://www.glasskulls.com/asending-sequence/)

The last picture shows our graphite crucibles disintegrating all over the furnace. That's why you should use a different material, I guess...

When you're casting metal, you can just quench your investment in cold water and it will pop right off, giving you access to your pieces. However, glass cracks when cooled too quickly, so you'll have to let it slow cool. Turn your furnace off and let it sit until it returns to room temperature.

Comments

[Chris Logan]

Cooling metal too quickly can generate cracks. But almost always leaves a less-desirable molecular structure.

Don't cool it faster than you have to.

[SelkeyMoonbeam]

Would you recommend quenching & annealing?

[Chris Logan]

Not unless you have very specific requirements for material properties.

Cooling iron, zinc, steel in cold water will leave microfractures throughout the surface if it doesn't shatter the part outright.

Cooling aluminum, magnesium results in a stupidly soft and unmachinable alloy, regardless of your starting material. 6061 after a water quench ends up with properties like 1001.

Just let your parts air cool. You avoid putting unnecessary molecular and physical stress on them.

[Chris Logan]

Air cooling avoids that stress. And results in a part that is easier to machine or handwork finished.

[Chris Logan]

Additionally, your graphite, that's dissolving away, is just oxidizing into oblivion... CO2 generation.

I'm sure some of it was absorbed by the glass.