DIY Microwave Kiln | Fuse Glass in Your Microwave

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About: Innovative Projects, Diy's, Life Hacks

In this Instructable, we'll look into way to make a microwave kiln.

For those who don't know what is a microwave kiln, here is a quick introduction.

Microwave kiln is a kiln that you can put in your regular microwave oven.

It does not use a wire heating element or gas to heat up. Microwave kiln is covered with silicon carbide.

Silicon carbide absorbs microwaves and turns them into heat.

Microwave kilns are usually used to fuse glass.

You can turn broken glass into amazing jewelry.

After reading comments, I realized that a lot of people did not know that microwave kilns exist.

You can easily buy one from amazon, ebay, Aliexpress (check the supply list)

This DIY version is not limited with size and it's much more durable than most cheap microwave kiln.

There is so much more that you can do with microwave kilns.

I use a microwave kiln to burn out Wax or Pla from plaster molds. It works very good.

You can also melt metals, but more on that in another Instructable, since there is much better way to do it by using the same principle.

Supplies:

Amazon Affiliate links:

Step 1: Making a Plaster Ring Mold

First we need to make a plaster ring.

To do that, you can make a mold from EVA foam or you can use a 3D printed mold.

If you use EVA foam, just cut strips of foam and glue them in the circle on top of another piece of foam.

The first strip I wrapped around a cup and used cello tape to glue it together.

The second strip I overlapped and glued together with some glue.

Both foam rings were glued on top of another foam with some regular school glue.

Step 2: Making a Plaster Ring

It's important to make the plaster ring weak.
You can use Plaster of Paris or any other plaster as long as it's white. Most of construction plaster will work just fine. In general you want your plaster mix to be watery not creamy. If you used a 3D printed mold, wait for the plaster to start thickening before pouring it, so the mold does not leak.

You can wait for the plaster to dry naturally or you can dry it in the oven.

There is another, much quicker way to do it.

You can dry it in the microwave.

It's not how you would normally dry/cure the plaster. Microwaved plaster will not be very strong, but in this case it's Ok, since that's what we need.

Wait at least an hour before microwaving the plaster. If you do it earlier, it might shatter.

Put it on top of some paper towels and microwave it until the plaster feels dry.

It does not have to be 100% dry. Steam on the microwave walls will help you to judge when the plaster has dried.

I normally do it in one go since I know my microwaves.

The plaster this size takes less than 10 minutes to microwave dry.

If you want, you can stop the microwave half way to wipe down the walls and make sure it's not too hot.

Step 3: Close the Bottom

You need to close one of the sides with some kind of lid.

I normally use an electrical tape to attach it. If you used a 3D printed mold, just flip the base around and use that.

Step 4: Mixing the Sodium Silicate (Water Glass)

You'll need Sodium Silicate also known as Water-Glass.

In the picture you can see cured water glass with red food coloring added to it.
Now you know why it's called Water-Glass.

The one I used is 37%, but you can also use 40%.

We'll need to dilute it with water.

Mix it with water in ratio 1:2 by weight.

For example: 11g of Sodium Silicate and 22g of Water.

We'll put it in a small spray bottle that mists.

It's important for the bottle to be small and be able to mist the solution. If it's spraying too strong, it's not gonna work.

Step 5: Prepare Silicon Carbide

You'll need silicon carbide grit.

Any grit should works, but for this method it's better to use a grit that's not too coarse or too powdery.

Something in a range of 80 - 220 should work fine.

In this case, I used 80 grit silicon carbide.

Step 6: Covering the Plaster

First we'll wet the plaster walls with water and wait a minute for it to soak in.

Then we'll cover the walls with silicon carbide.

Use your finger to press the silicon carbide.

Step 7: Covering the Plaster

Next, we'll switch to water-glass mix we prepared earlier.

You will keep wetting and covering silicon carbide with more layers.

It's important NOT to over spray the water-glass solution.

Silicon carbide should feel slightly wet, but not too wet.

It's not necessary to spray it after every layer. Do it by the feel.

On average I spray it after every 2nd layer.

It's important to press the silicon carbide tightly together.

Step 8: Covering the Plaster

When desired thickness is achieved, use a coffee stirrer to remove excess material

Step 9: Covering the Plaster

Next we'll remove the lid and tidy up the other side.

If necessary you can spray some more water-glass

Step 10: Microwave Cure the Water-glass

You might know that water-glass can be cured with CO2.

We will not use CO2.

I am mentioning it only in case you have used CO2 before to cure water-glass that was mixed with sand.

We will put the plaster ring directly in the microwave as it is.

The microwaves will cure it.

Later we'll need ceramic fiber blanket (kaowool)

We'll use some of it now to protect the microwave and insulate the ring.

You should wear a respirator and gloves when working with ceramic fiber

Sandwich the ring between ceramic fiber blankets and microwave it until it glows red.

You want to do it in a well ventilated area, because burning plaster can stink.

With heat proof gloves on, take it out and remove the top blanket.

Let the ring cool down.

Once cooled, you should be able to peel off the plaster.

If the silicon carbide ring has cracked, most likely the plaster was too strong or you did not press the grit tightly together.

You want the plaster to crumble around the silicon carbide ring. If it's too strong, the silicon carbide will stick to it too good and when the plaster cracks the carbide will also crack.

You can also see what happens when you over spray the water-glass. It will bubble up cracking the silicon carbide.

Step 11: Sanding the Glass

Get a piece of glass (for example a glass from a picture frame)

Wrap the table with plastic wrap, so the glass does not move.

We'll pour some silicon carbide on top and add water.

Use a drinking glass (or any piece of glass that's flat) to sand it.

Now we can use the glass to sand the ring and later the kiln.

Step 12: Finishing the Silicon Carbide Ring

Add tiny amount of water and sand the ring from both sides.

Brush off the excess grit and put the ring in the microwave to dry it.

At this point you can spray some more water-glass (if necessary) to make the ring stronger.

After that, microwave dry it again.

The ring weights about 40g and is 4mm thick.

Step 13: Wrapping With Ceramic Fiber Blanket

I cut 2 strips of ceramic fiber

Then I cut ends of strips in angle and wrapped them around the ring.

I did the same thing with the other strip.

I cut it to size, chopped the ends in 45-ish degree angle and wrapped around the first strip.

Then I used rubber bands to keep the strips from unwrapping.

Give it a roll to make sure everything sits in place nicely.

Step 14: Preparing the Water-Glass

We'll use sodium silicate again, but this time as it is. You don't need to add any water.

Instead, well add some food coloring.

Food coloring will make it easier to see where we brush it.

Step 15: Glue It With Water-Glass

We'll glue the strip to itself to keep it from unwrapping.

Do not brush water-glass under the fiber sheet, brush it only on top.

I explain why in step 31

Then I put it in the microwave to cure the water-glass.

If you used food coloring, the water-glass will most likely turn brown (not always).

Without the food coloring, it will be white, so it's harder to see.

No we can remove the rubber bands. Sometimes they break in the microwave, so don't get scared if you hear a weird noise :)

Step 16: "Sanding" the Ceramic Fiber

We'll wrap the kiln with a cling film to keep the fiber layers from separating.

You want to cut off the excess cling film from top and the bottom, leaving it only on the sides.

We'll use the glass again.

Add generous amounts of water and let the kiln soak it.

Then start slowly sanding it.

hmmm.....Sanding is maybe not the correct word to use.

The glass will give you much better result than sandpaper.

You will want to do it on both sides.

Then we'll put it in the microwave to dry it

Step 17: Covering Rest of the Kiln With Water-Glass

We'll remove the plastic wrap and cover the kiln with water-glass.

Then we'll microwave cure it.

I did it in 2 parts, so it would not stick to the fiber blanket.

At this stage, Do Not overheat the kiln!

Once the water-glass appears to be set, that's it.

Don't heat it more!

I explain why in step 31

Step 18: Heating Up the Water-Glass

You will want to heat up the sodium silicate with a blowtorch.

Since I have a heat-gun, I like to start with that, but that's optional.

Blowtorch is what you need.

By heating up the sodium silicate, you will change its properties.

It will bubble up and look like stone.

I explain why in step 31

Step 19: Sanding the "Popcorn"

After blow-torching the kiln, it will look like a popcorn ceiling in some spots.

We don't want too much of this effect.

So we'll sand it a little bit.

Again, I explain why in step 31

Step 20: Sealing the Stone Like Water-glass With Water-glass

I diluted the leftover water-glass with water in ratio 1:2

Then I brushed it on top of the "stone like water-glass" to make it stronger.

After microwave drying it, I added another layer and dried it again.

Step 21: Enlarging the Hole

I cut one of the holes bigger and sanded both ends of the kiln one more time.

Then I microwave dried it for the last time.

Step 22: Making the Base

I put the kiln on top of 2 ceramic fiber sheets, so I could cut out the base in the shape of a kiln.

I sprayed some water between the sheets, so the blankets would hold together better while I work on them.

Step 23: Making the Base

I covered the top and sides with water-glass.

Just like when gluing strips, you don't want to brush any water-glass between the sheets of ceramic fiber.

They are held together only by the water-glass that's brushed on sides.

Step 24: Making the Base

After microwave curing the sodium silicate, the base was sanded.

As you can see, I did not cover the whole side with the water-glass. We'll do it after sanding it.

I also did not use a cling film this time. It's because we're sanding the blanket the flat side down

After sanding it, I finished covering the sides with sodium silicate.

Step 25: Making the Base

I felt like it needed some more water-glass

Step 26: Making the Base

I did the same thing that I did with the kiln.

Blowtorches the water-glass, sanded the popcorn, sealed with 1:2 ratio water-glass

Step 27: Making the Base

I used 2 packets of Sugru to add silicon feet.

Step 28: Making the Lid

The same way I made a lid, but only a single blanket thick

Step 29: Finish!

Now we can fuse some glass.

You don't want to put glass directly on the base, because it will stick to it.

We'll use ceramic fiber kiln paper. It's made for this purpose.

Fusing times will depend on the size of your kiln, the power of your microwave and whether or not you use the glass turntable.

In this microwave it takes about 4 minutes to fuse the glass.

I am not using gloves, because the kiln is only warm when I take it out from the microwave.

The temperature will keep rising and after a few minutes the kiln will be hot, but by that time it will be sitting somewhere to cool down.

Step 30: A Different Microwave

Here I am using an 800w microwave.

In this microwave it takes under 3 minutes to fuse glass.

Of course fusing the glass that fast is not always the best thing to do.

Sometimes it's better to turn down the microwave power to achieve better results.

Step 31: Why Did We Blow-torch It, Sanded the Popcorn and Did Not Brush Water-glass Between the Fiber Blankets?

We did all those things to avoid possible microwave arcing and the water-glass heating up on its own.

Water-glass behaves similar to glass when microwaved.

If you heat up glass with a blowtorch in one spot and put it in the microwave, it will keep heating up. I demonstrate it by heating up a glass plate and then putting it in a microwave.

You can see that it kept heating up. The same thing can happen with water-glass.

In the picture you can see a kiln with a hole that's glowing hot.

The thing that's glowing is not silicon carbide, it's water-glass.

That's why we heat it with a blowtorch so it appears less glass like and more stone like.

We sanded the popcorn for the same reason. To avoid possible arcing, because of weird shapes that could have glass like structure.

It's also why you don't want to brush water-glass between the sheets. You will not be able to heat it up to make it appear less glass like.

Of course you will not always get these problems.

Some of my early kilns have glued blankets and popcorn pattern and they work fine, but you never know.

That's why it's better to be safe than sorry.

Speaking about the glass turntable. For the same reasons, It can make your kiln heat up slower, especially when it's warm.

Step 32: Microwave Kilns Are Awesome!

Here you can see one of my early kilns that I have used a lot.

It's a 3 piece kiln with 3 large silicon carbide rings.

I use it mainly for burning out wax or pla from plaster molds.

If you wonder how it fits in the microwave, you just flip the microwave on the side.

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    81 Discussions

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    needfulthing

    17 hours ago

    Very cool project, I didn't know this was possible in a microwave. I wonder if this might be an alternative to finish metal clay instead of just burning it on a metal mesh with a torch. Although I'm a little worried about temperature control in this case.

    1 reply
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    arclite7needfulthing

    Reply 7 hours ago

    Absolutely so Needfullthing! I am thinking just as yourself and the "ceramic paper" referred to by ShakeTheFuture as a clean flat support surface sounds perfect for example before solving many 3D shaped profiles like artisan-al wedding bands? Should they be created flat? Then rolled up and welded/brazed before sizing as a complete process? Has anybody seen a 3D printer adaptation for liquid clay printing? The results would likely be spectacular if not extremely expensive finished artefacts when sold in Japan. Cloisonné preparation would be somewhat less time consuming by this method instead of by traditional wire brazing? I instinctively look to Japan for their celebration of innovation and modernisation without loosing quality. This kiln is the best thing since sliced bread, I still think! Good luck with your ideas too...

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    Jan5412

    Tip 3 days ago

    Observe the necessary safety requirements because Silicon Carbide may be carcinogenic.
    There is still much uncertainty about it, but prevention is better than cure.

    9 replies
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    a-morpheusJan5412

    Reply 2 days ago

    I'd never heard of that risk, so thanks. That said, thinking of the literally millions of silicon carbide grinding wheels in use in shops everywhere over the past decades...makes me think it's not super bad. Powdered SiC might be, as many minerals/metals in powder form become very to extremely toxic...can't find the reference where I read that right now unfortunately. I don't think 80 grit is a powder. Although it's just one reference this document from an abrasives specialist manufacturer says "Abrasive powders commonly refer to any size finer than #240 grit" (http://kcabrasive.com/projects/gritpowdersizing.pd....
    This "systematic review" (https://www.ncbi.nlm.nih.gov/pubmed/27628329), says, "The increased risk of lung cancer detected in the SiC production industry appears to be associated with high exposure levels to total dust, including crystalline silica and cristobalite which occurred in this industry in the past decades. It may not persist under current exposure circumstances, characterized by lower levels and use of personal protection equipment. Commercial users of SiC-based products were not affected."
    This other document refers fibers of SiC being an issue: "Nonfibrous particles have low to very low toxic effects on lung tissue. Silicon carbide fibers, on the other hand, can cause lung fibrosis, lung cancer, and possibly mesothelioma." (https://hazmap.nlm.nih.gov/category-details?id=624&table=copytblagents)

    So to me the main question of safety regarding SiC in this furnace is, does heating the 80 grit particle generate silicon carbide fibers somehow? If not I don't see much of any toxicity issue.

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    AlexandraC62a-morpheus

    Reply 2 days ago

    Incorrect reference due to typographic error. Fibrous silica was intended as hazardous and not inclusive of non-fibrous silicon carbide crystals as a hazardous environment for furnace loaders during the large scale manufacturing process from raw materials. Dust hazards are recognised. SiC fibres are not referred to at all as they are not present and are not intended to be referred to.

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    a-morpheusAlexandraC62

    Reply 20 hours ago

    I'm trying to understand your comment but I'm not sure which typo or link you're referring to. The first linked doc talks about dust being a problem, the 2nd talks about fibers of SiC being a problem. I don't get where something was unclear or incorrect... I must be missing something obvious.

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    arclite7a-morpheus

    Reply 9 hours ago

    I looked at your reference in PubMed, These research write-ups are usually extremely precise and matter of fact but in this case the 'English language' is a little non-standard to which I propose there is no intended reference to SiC crystals as carcinogenic just as fibrous SiC is not intended as a reference. If it were the subject of a serious indictment the reference to such would indeed be precise and not resting on a weak syntactical bridge as this "a typographical error" leading to ambiguity. The best approach to this would be to contact the papers author(s) and to ask for clarification - this may be of good service leading to an amendment and refocus of the papers intended statement. My approach is as a person with autism. I am not writing in any sense of a rebuke, your comment is fair just as is my observation of a writing style in context to many others also observed as fit for purpose. This may sound a little "Sheldonesque" but ambiguities really cause me problems I must seek to resolve! I thank you for your reply.

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    AlexandraC62a-morpheus

    Reply 2 days ago

    The closest association would be nano-particles as the cross-section of fibre ends resembles these structures for their electro-physical and chemical effects when they puncture cell walls and their internal structures. Is SiC found or manufactured as fibres as was asbestos for many years so still claiming many lives - Turner Newel were found manufacturing blue asbestos in South Africa using an exclusive black workforce years after medical evidence forced them to shut down their European/British plant. A SiC pattern of racist supremacy hopefully never to be repeated! We are all brothers and sisters proven by mitochondrial Eve our first hominid ancestor who lived in Africa and who was black. I am like everybody else her descendent. A white allele was selected as we travelled Northwards where sunlight was significantly weaker and our skin was less able to create vitamin 'D' essential for strong bones. That selection was long ago and can be seen today in countries like Norway and Finland where fair hair and blue eyes are a common trait. But supremacy is a falsehood Bourne out of ignorance of our shared history. Thank you for continuing this wonderful tradition of human celebration of difference.

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    AlexandraC62a-morpheus

    Reply 2 days ago

    Best place to look for current medical research with the most powerful search engine and personal document collection system is PubMed, google this to access public entrance, second to nothing else for public awareness!!! If SiC poses any risk, you will first find collected evidence here. Thank you for excellent work and Copyleft intelligence.

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    Quantumdusta-morpheus

    Reply 2 days ago

    You have the correct approach !
    SiC fibers are generated only by the process used to make SiC abrasives as a by -product. SiC fibers are also made on purpose as additives to other materials to change their properties. Working inside these plants without protection can lead to carcinogenic symptoms over time. Using, heating or any other common abrasive/grinding purpose for SiC will NOT produces the fibers.

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    Frank1450

    15 hours ago

    Excellent instructions!

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    charlessenf-gm

    17 hours ago

    Easily one of the best Instructable videos I've seen to date. Absolutely no interest in fusing glass, but seriously tempted to make one of these after watching you do it!

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    natblondeartist

    2 days ago

    This is a great tutorial! Any chance you sell these kilns?
    I am a working artist, however current circumstances prevent me from being able to make my own. Please let me know!

    2 replies

    Thank You!
    I don't sell these kilns, but you can easily buy one from amazon (check the supply list) or if you look around (aliexpress), you can find them even cheaper.

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    ToniM95

    Question 1 day ago

    When will you have the feature on melting metal? My an used to be a machinist and is always looking for more ways to work metel

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    kmpres

    2 days ago

    I had no idea this was possible. Looking forward to the lost PLA method of metal molding using one of these.

    1 reply