One of the newer toys in our lab is a microwave kiln. A microwave kiln is a device which you place in a conventional microwave and it acts like a kiln. Microwaves kilns are commercially available from various places on the internet.
It is composed of a porous ceramic body (likely alumina) with a ring or inside coating of high temperature susceptor material (the black colored material). Susceptor materials are materials that absorb microwave energy (like water, fats, oils, etc). There are a wide variety of susceptor materials some of which reach very high temperatures -> 1800 degs F. These materials are generally a patented or trade secret material combination – think graphite, magnetite, and/or various iron oxides.
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There propose along with the microwave oven is the bring the fired item in the kiln to high temperature in a short period of time (think 6-12 minutes).
We purchased one of these toys and have been exploring its usefulness.
We are using a standard 1000 watt home microwave. We placed a fun-u-factured flower into the microwave kiln. Closed the door. Set the timer on 9 minutes. We pressed start….
{Note the glow from the inside.}
Microwave kilns and microwave kiln processing of glass and ceramics have been around for over twenty years (thus its really not a new technology). The availability of low cost ($75-$175) microwave kilns has only happened in the last couple of years. We have found that there is quite a bit of variability in the results (there are some issues in getting repeatable results).
Lastly, we encourage you to try these out as they are reasonable in cost and may have a place in your lab/studio. We caution you to read and follow ALL of the manufacturers instructions. Happy cooking!
I picked up a microwave kiln for $99 last fall – and had tons of fun violating all of the rules of glass…with help. To begin with, I have a 1200 watt microwave, and I also bought a fair amount of kiln paper in various thicknesses. I was able to create 1/2″ glass pieces that were fully fused within cut-outs formed from the kiln paper/padding, but stopped after only a couple weeks once I realized (after more online research) that the burn off from my microwave kiln might add itself to my food since I was using the same microwave for both.
I do want to utilize the microwave kiln, and it works, but I’m holding off on any additional experiments until I pick up a microwave from goodwill that I can devote solely to glass fusing. I would advise that you do the same. That being said, “power” is not the big thing, I actually had to step mine down, as anything over 1000 watts, at least with the microwave kiln I purchased, actually seemed to be detrimental to the process.
The cooling/annealing process is also less clear with microwave kilns. Upon removing the microwave kiln from the oven, I would place it on a “bed” of 2 bricks, and place a 3rd over the hole in the top – then leave it overnight. Not exactly the annealing process as outlined in your standard glass books – but I’ve dropped some of the pendants I made, and they haven’t even chipped.
Dawn, you REALLY never want to share/reuse anything that you use for food. We’re glad to hear some success stories for microwave-kilns. It has been iffy at best for us. Perhaps we shouldn’t have purchase a re-furbished microwave. You could use a fiberfrax blanket to cover your microwave kiln to slow down cooling and aid in annealing (although annealing has set temperature/time schedules). If you are using borosilicate glass, annealing may not be such a big issue (especially if you pieces are thin).
psst. it’s spelled susceptor.
why is there a big hole in the top? to let out all the heat?
Fenn, thanks for pointing that out. I think the spelling checker didn’t like susceptor and suggested suspector (as perhaps an evil villain).
As for the hole in the top, it’s a commercially sold device. Hmm? Letting out all the heat (you say)? Seems very likely. If one is processing glass, once the glass is above red glow, it starts to become conductive (thus becomes its own heating device) and thus heat loss may not be as big of an issue. Our biggest issue with the device is the inconsistency of the results.
We have melted the rotating glass tray to the floor of the microwave (which was pretty interesting). Thanks for the assist.
[...] such as sugar, ceramic, and glass. Take a look through their archives. We found the post on microwave kilns interesting, as well as the writeup about Shapeways glass printing which is seen above. We’ve [...]
The hole in the top is for allowing air, steam and vapours to escape and to allow air back in when it cools down. Quantum physics teaches us that this small hole releases only very little heat.
Maggy, thanks for the info.
Can you fuse nichrome metal into glass in the microwave kilns for a jewelry finding? I know you aren’t supposed to put metal into a microwave, but thought maybe the micro wave kiln might make it work?
Smooth metal in a microwave is not a real issue (sharp or thin pieces of metal produces problems including wire). If you are looking for entertainment, check the web for “interesting things in your microwave”. That being said, you could get two pieces of boro glass to
hot-tack state, open the microwave kiln and put the nichrome wire in the boro sandwhich.
Dear sir
shell we make microwave kiln to fuse glass?
Yes, we’ve been using the microwave kiln for fusing glass.
Can you use recycled glass bits, such ass broken green, brown and blue beer bottles?
Yes, you can use any type of glass. However, different glass bottles have different coefficients of thermal expansion which might make them incompatible with one another and cause cracking. You will need to do some testing.