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How to fuse glass in a microwave? Time, glass layout, placement, confetti? Answered



3 years ago

you can actually melt glass in a microwave quite easily. The material in the microwave kiln is a microwave susceptor. Typically, this is silicon carbide, available as a powder. It's mixed with refractory material. Once the glass becomes hot (as a result of the hot silicon carbide), it actually becomes a microwave susceptor. The hot glass will begin to glow red, eventually melting under the effects of the RF energy.

News for the fun of it:  Most glass is transparent to microwaves - just like light...until something happens...something neat.

Heat up a piece of glass to 'near glowing' with a torch...then put it in a microwave.  You will notice the HOT glass is now opaque to the high energy waves, and absorbs them - all of them - and starts to get hotter and hotter.

If you can uniformly get your piece up to a suitable temperature (guessin here - around 600 celcius, just below glowing hot) then toss it in the microwave, the oven should take it the rest of the way.

That's kind of epically cool. Utterly useless for the purpose of creating fused glass artwork, but you gotta love beer bottle plasma.

I figure if you could equally preheat the object (probably from below) with a limited amount of heat, then a microwave would be just the ticket - you'd need an upgraded diffuser and ceramic turntable, but I think it would work.

Yeah, now that I think about it, the microwave kiln probably only generates enough heat to make the glass inside visible to the microwaves, and the glass takes it from there.
It's the preheating and controlled cooling that are potentially problematic, I think. Presumably the preheating could be done outside the microwave in a gas or electric mini-oven thingy, but great care would have to be taken when moving the glass into the microwave, to prevent the pieces shifting before they're fused. Better to preheat inside the microwave if possible. For the same reason, it would be best to use a stationary ceramic base rather than a turntable.
The cooldown is the real trick.  Controlled annealing and cooldown are critical to fusing glass successfully. The pieces that fit in my little microwave kiln are small enough that just letting the kiln cool naturally is mostly sufficient to relieve the worst of the internal stresses in the glass. Larger pieces need a much slower annealing/cooldown period, so some provision would have to be made to allow for that.
Sounds like kind of a fun project to figure out.

perhaps taking the klystron/magnetron out of a microwave and fitting it to aim at a fixed small space surrounded by heated ceramic bricks to form an oven for the preheat and cooldown...

It sounds to me like if we're talking about surrounding the piece with heated ceramic bricks (which I think is great), maybe the answer is just to build a larger version of the mini-kiln I have, with the mettalic coating inside and a microwave-safe  temperature sensor of some kind to allow for the kind of control that larger pieces need.
I wonder what that coating is made of. I have a bunch of kiln bricks I'm not using....

...this works because glass becomes electrically conductive above about 600 C., and more conductive the hotter it gets. Big glass plants keep the melt liquid by heating with damned big rods carrying a lot fo current, pushed into the glass.

You'll need a microwave glass fusing kiln. It won't work without one.
The biggest downside to microwave glass kilns is that they are small. You can only do one piece at a time, and the pieces can't be much larger than about 1 1/4" in diameter. The upside is that is only takes 3-4 minutes to fuse a piece in the microwave, and another half-hour or so to cool down.
I'm not sure what you mean by glass layout, placement, confetti - these would be design considerations, so it would depend on what you wanted to make.
I have a microwave kiln and it's fun to play with, but for serious pieces you'll want a real kiln eventually.

What causes it to heat?  I know about the microwaves but what are the microwaves acting on?

The kiln itself is just a round refractory ceramic fiber box (flattish bottom piece with a domed lid). The inside of the lid is coated with a metallic coating, kind of like the silvery-grayish stuff on the inside of a Hot Pocket sleeve, only more so. Your just stick it in the microwave and the metallic coating gets nice and hot inside the kiln. Mine has achieved temperatures in excess of 1500 F, if my eyeball analysis is accurate.

 I think the kilns are made of some kind of ceramic that microwaves can heat.  I know that things like granite and some others also have this property.

I would be surprised if you could heat glass very hot in a microwave.