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.
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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.