DIY Glass Kiln from Ceramic Fiber Board Insulation

120 VAC and 20 amps

Building this kiln was a process of experimentation, adjustment, and a fair amount of trial and error. If you’re considering a similar build, hopefully this saves you some time and helps you avoid a few of the pitfalls along the way.

This kiln design does not include any built-in temperature control. To operate it safely and effectively, you will need to use an external kiln controller or other temperature-regulating device.

I built this kiln several years ago and am sharing these photos and construction ideas simply as suggestions for how you might approach building something similar. When I constructed mine, I had seen a somewhat similar design online, but I did not know if my version would actually work. The materials and dimensions I chose were largely based on educated guesses and experimentation—fortunately, the result has performed well through many firings.

For the frame, I used a MIG welder to tack the metal pieces together. However, the frame could likely be assembled with bolts instead if welding equipment is not available.

This kiln was built in 2022, before AI tools were widely available. Today, those tools may be helpful for planning dimensions, calculating heating elements, or troubleshooting design questions as you build your own version.

A WORD OF EXTREME CAUTION!!

My limited experience at the time meant there were risks I did not fully appreciate when I began this build. If I had not taken precautions and remained prepared for problems, I could easily have caused serious damage—possibly even a fire in my shop. As you look further into this project, you will likely see the kinds of issues I’m referring to.

For that reason, approach a build like this carefully. Take the time to understand the electrical and heating aspects involved and make sure appropriate safety measures are in place before operating the kiln.

I’ll organize this into groups of photos that illustrate the main stages of the build. Each section focuses on a particular task or decision that was part of the process.

1. Working with the ceramic fiber boards.
2. Treating the boards with rigidizer to improve their strength and make them easier to handle and cut.
3. Cutting the boards to the required dimensions.
4. Determining the specifications for the quartz tubes and cutting them to length.
5. Heating element specifications —diameter, length, and resistance required.
6. Winding the heating elements and installing them in the tubes.
7. Planning and building a simple metal frame using angle iron to hold the boards together.
8. Thermocouple considerations for temperature measurement and controller input.
9. Burnout of the manufacturing binders in the boards — CAUTION HERE!

These steps reflect the approach I took and are intended mainly as a reference to show the general sequence of the build.

The overall size of this particular product worked out extremely well for project.

Before handling the material, read this article concerning safety.

It references ceramic fiber blankets, but it pertains to the boards/sheets also.

Ceramic Fiber Blanket Safety | Handling and Installation Guidelines.

Untreated ceramic fiber boards are extremely fragile. Without a hardening agent, they are highly susceptible to chipping, denting, and edge wear. Even light handling or an accidental bump can cause irreversible damage, as there is no simple way to “patch” the material once it breaks.

The rigidizer acts as a silica‑based “glue” that locks the fibers together, significantly increasing the board’s durability. I used a spray bottle to apply a fine, even mist across the face of the board.

The edges and corners are the most vulnerable areas. I used a brush to apply heavy, soaking coats in those spots. Remember that cutting the board will create raw, untreated edges that will require immediate treatment.

You can dilute the rigidizer with water to help it go farther, but keep in mind that the rigidizer works by leaving silica behind as the water evaporates. Higher dilution means more liquid must evaporate before the board hardens.

You can use any heat source to speed up the evaporation process. Once fully dry, the boards will feel noticeably harder and more structural.

Even after the rigidizer has set, the boards still contain factory binders. During the first kiln firing, these binders will burn off. This is a normal part of the curing process—more on that later.

This drawing shows the way I chose to cut the sheets. One sheet will be the top and bottom and the second the front, back, and sides.

Before you go further, did you see the article about the safety concerns?

I used a small cordless circular saw to cut the sheets.

As you can tell by the method I chose to cut the sheets, I should have been much more careful! I did use a face/eye shield along with an N95 mask, along with being very careful about vacuuming and cleaning up the area. Just be aware of the risks.

As you can see from the photos, I used a large metal square as a guide for the saw.

I should have taken more pictures of the top and bottom pieces to show how they are meant to be fitted INSIDE the perimeter of the walls. You may be able to get an idea from one of the photos that I marked up. I made a lip that was 3/4 the thickness of the material. Basically, a 1/2" section that would extend into the chamber once fitted. Keep in mind the quartz elements and how close you want them to the top.

I purchased two clear fused quartz tubes 12mm x 14mm x 4ft from Whale Apparatus. I also purchased a diamond cut-off wheel #545 for my Dremel. The tubing was much easier to cut then I had expected. Again, take necessary precautions with face and eye protection etc. Cut slow without applying pressure. I made a jig from some paper clips to hold the tube and make it easy to turn while cutting.

I waited until I cut the notches in the side walls for the tubes. before deciding how long to cut the tube length.

I tried to space the tubes out evenly and I used masking tape for my template. I used a small hobby saw that I had to make the notches. A blade from a hacksaw would work also.

Power Design:

1. Power = 120v x 120v / 6.44 Ω = 2,236 Watts
2. Current = 2236 Watts / 120v = 18.6 A

Element Design:

1. 16-ga Kanthal A1: ≈0.269 Ω/ft
2. Total wire: 24 ft
3. 4 elements in series
4. Wire per element: 24ft / 4 elements = 6 ft ea
5. Mandrel circumference: 0.79 in ( 1/4" rod)
6. Total turns calculated: 377
7. Turns per element: 377/4 = 94.25
8. Coil length before stretching ≈ 4.8"
9. Stretched coil: ≈ 17"
10. Resistance/element = 6ft. × 0.269 ≈ 1.61 Ω
11. Total resistance: = 4 elements × ≈ 1.61 Ω = ≈ 6.44 Ω

Quartz Tube:

1. Size: 12mm I.D. x 14mm O.D. x 4 ft.

I used 6ft of wire for each coil. Don't worry about the exact number of turns. Just use a 1/4" rod and the entire 4 ft length of wire. I found this video very helpful.

Easy Coil Heating Element Winding Jig

A pigtail will have to be added to the end of the coil. It will make it more durable and easier to make electrical connections. I made a simple little jig to help me hold and twist the pigtail. Try not to pinch, smash, or scratch the element wire.

I realize that not everyone is going to have an old unused metal storage shelf, but at least these pictures will give you some idea of the basic structure. Absent an old shelf as I had, you'll have to come up with some steel angle iron. I would NOT use aluminum. I don't know whether it would work or not. I did, however, use a piece of aluminum against the side wall when I mounted the thermocouple and it appears to be okay.

Just know that the frame only has to hold the pieces together. The frame just fits snuggly, but not tight. If it is too tight you will chip the corners or edges trying to fit it in place.

Once constructed, the pieces should fit together firmly and not feel loose or floppy.

The hinges were made from some 4" x 6" x 1/8" aluminum plates I had. I used a hacksaw and rubber mallet to cut and form the pieces. Notice the rest stop I added to hold the lid open. I had to play with getting the angle just right to keep it from coming closed or tipping over. Turned out to be a delicate balance, and I was lucky that it all worked out. The handle was simple enough, just a piece of fiberglass tubing I had saved. If I had to guess, I think it came from my old pole saw.

I picked a thermocouple with the same look and mounting style as one used in a commercial kiln. It’s rated for 1300 °C (2372 °F). It was necessary to make it shorter. I mounted an aluminum plate to the outside frame bottom on one side and then drilled about a half a half inch hole through the plate and the kiln wall. The thermocouple had several 3/4 ceramic segments running the length of the probe. I removed some of the segments and cut off the excess length. I used the same Dremel and blade that I used for cutting the quartz tubes.

I cut and then inserted some ceramic tubes through the wall of kiln. This kept the pigtail ends of the element wire from touching the wall. All the elements were then inserted into place.

I used 10ga wire that would tolerate heat and some heavy duty copper connectors. I added a 20 amp switch and a 120vac pilot lamp. The switch is for emergency off and the lamp indicates whether the elements are being turned on or off. A fuse and an over temp thermostat could also be connected at this time. Put them in series also.

To protect the electrical connections, I fashioned a cover box using one of the shelves from the storage cabinet. I also used a scrap piece of perforated stainless steel fabrication sheet. All that was needed to make it was a hacksaw, rubber hammer, and some pop rivets. Both boxes were identical except for some holes for the cord, switch, and pilot lamp.

Burning the byproducts out of material like this is a common process if you were to make your own kiln shelfs. You can find information online that addresses the concerns and expectations. I took the temperature up to 600 degrees (the material will be turn totally BLACK) and I left it there for an hour, after which took it up to 1200 degree and left it there for at least another hour. The two temperature steps are recommended. The process is finished when it has turned white again and all looks as though the cooking process has stopped.

Not knowing what to expect, I took some very basic precautions, but as you can see by the photos and the video clip, I made a very stupid mistake. I inadvertently left a piece of hardboard on the outside bottom of the kiln. When I took the photo, I had already removed the bottom floor of the kiln - it was not damaged, in fact none of the kiln was damaged. I had used the hardboard as a shim at one point while adjusting the hinges and forgot to remove it.

As a precaution, I placed the kiln on a portable steel table. I opened up my shop as much as possible and placed a fan to blow over the area. I also, made sure I had access to a fire extinguisher.

Now, is this safe to do for a DIY project? I would say yes, if you know what to expect. There should NOT have been a fire!! That was my fault due to a mistake I made.

All things considered, what should you expect. The kiln is going to get very hot and turn black. Not to worry though, it will again turn totally white on the inside and leave the exterior with various shades of white and brown. Some of my scorched look was actually from the fire I caused and not the process itself.

You can expect a very bad smell/smoke, toxic? I suspect it could be. I wore a mask with carbon filtration, plus I tried to stay away from the area until the part where I had to intervene.

The only thing I would do differently if I were to do this again, is double check for anything flammable touching the kiln. Also, more ventilation under the kiln. Remember, I had a lot of ventilation happening and directed it all out of the shop.

I am happy with the way this project turned out. The only precaution is too make sure you have a fireproof surface underneath with plenty of room for air movement all around. It really does not get hot enough on the top or bottom to burn you instantly or set something on fire very easily. I am pleased with how cool it actually stays.

My wife had a much smaller kiln when she first started fusing. Had we known better at the time, we never should had purchased the kiln. It turned out to be a "bead" kiln, that was meant for annealing. Despite its limitations, it was able to reach approximately 1600 °F, meaning it could theoretically be used for fusing if paired with adequate temperature control. With only a mechanical thermostat and a tiny temperature gauge, I had to build a full controller from scratch to manage the glass‑fusing stages.

The controller I made to operate the kiln has two rpi zero w(s). One controls the heating process while the other uses a separate thermocouple for overall safety monitoring. A local web page allows adding, storing, and editing various fusing programs and starting the fusing process. A status page keeps me updated. Monitoring can also be done via Node-RED and it has a nice graphical display for temperature and history.

Several fail safes are employed to completely disable all power to kiln should the main controller quit functioning properly or the main AC power drop out and come back on, which could possibly leave the kiln in an unsafe mode. The system will notify me via a text message alert when a danger is sensed. Temperature can be monitored remotely on any networked device. If there were to be enough interest in any part of the controller, I could provide more information but, it's still in a state of flux.

If you made it through this far and appreciate me sharing my experience of this project with you, please consider buying me a cup of coffee. Thank you for your interest!