Cracking on Mirrored Acrylic

Can someone tell me why my mirrored acrylic is cracking this way? I masked it on both sides. When it comes out of the glow forge it is fine, but starts to crack shortly after.

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Did you clean it with alcohol?


Alcohol for cleaning???

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Stress fractures from the heat - especially at the sharp interior corners. Try making all those outer cuts slightly rounded.


Or annealing.

Pop it in the oven for an hour at a non melting point and then let it naturally cool in there. It’ll realign the molecules so there’s isn’t all the stress in spots.

Should still shy away from alcohol as a cleaner. Ammonia base is okay.



The traditional formula is 170F for one hour per mm of thickness to fully anneal. Less time will result in partial annealing which is often good enough. Temps higher than 200 are to be avoided as they can start to raise air bubbles in the surface and anything over 250-270 can warp & even slump the acrylic.