Microwave Kiln Uh-Ohs and How to Deal with Them!

Fuseworks Microwave Kiln Fused GlassWe all make the occasional “oops”, that’s why Diamond Tech is here to help. Keep in mind that practice makes perfect and if you follow the instructions and these pointers for preventing and sometimes fixing a fusing flub, you’ll be churning out awesome art in no time!




Arg, I have air bubbles under my glass!

Make sure the layers are laying flat. Edges fuse before the center, so cut your base glass 1/8” larger than the top layer to      allow air to escape.

Err, my edges are uneven!

Uneven edges generally occur if you didn’t fire it long enough or to a high enough temperature for a full fuse, continue firing in 30 seconds intervals to reach desired effect.

Oh, no! My edges look like a porcupine.

The piece was fired too long. The spiked edges are caused by the glass grabbing as it is trying to shrink.

My glass is toooo flat!

Again over firing is the culprit. Reduce your power and shorten your time. After your first firing inspect the piece, continue firing in 30 seconds intervals to reach desired effect.

I wanted a different size!

Glass naturally reaches ¼” thickness when heated. Your glass will shrink or expand to obtain this depth.

My glass is repelling.

This happens when different coatings like dichroic and iridized coatings are fused together. To avoid this, encase the coated glass with separate non-coated glass.

There’s a white gunk on my glass.

This can happen if your glass remains between 1000ºF-1300ºF too long or by cleaning glass with a slew of cleaning products; clean your glass with diluted vinegar or water.

My edges are gray and scummy, gross!

This usually happens when a piece is fired once and then cold worked before refiring. Cold working involves using either a grinder or glass saw on a piece of glass. Scrub completely after cold working and dry before refiring.

My piece has cracked!

This can happen from thermal shock or glass incompatibility. Thermal shock happens by exposing the hot glass to cool air to soon or by heating too quickly (an “S” shape appears). If the crack occurs where two pieces of glass meet, the two pieces are not compatible. Make sure your glass has the same COE (coefficient of expansion).

My glass has shattered, much like my hopes

Don’t give up yet! Pieces over 1” with more than 1 layer may sometimes shatter. Make sure your glass is clean and dry and fire at a lower power.


If you have any questions, please ask away in our comments section, we would love to hear from you! Check out our Creative Corner for more how-to and a flurry of fun fusing projects.