You Can Use Glass in Your Ceramics Kiln (Who Knew!)

All of these examples were done by 6-9 year old students!
All of these examples were done by 6-9 year old students. Photo courtesy of Ed Hoy’s International.

Imagine this scenario: You open the kiln for the first time after a ceramics project’s glaze firing, and peek inside. An array of colors and textures, perfect little projects to send home stare back at you, just waiting to be shared. They are guaranteed to get a WOW from parents and are likely to be kept in glass cabinets and window sills for years to come. I still have pieces of clay I did in school, don’t you?

Sadly, clay is usually one of the only media in the art room that has this profound impact because it feels real, solid, and tangible to students. I am left wishing there were more opportunities for students to work with unique materials like this, but frankly, the options out there can be intimidating. It just so happened last spring at NAEA I was browsing the exhibitors floor, I ran into Maria from the glass art supplier, Ed Hoy’s International. We got to talking about all the options for using glass in the art room and I was instantly intrigued.  I had never ventured forth using glass in my kiln, in fact, I didn’t even know I could! I was eager to learn more from Maria (she is really a wealth of information) and I wanted to share my findings with all of you.

Ed Hoy's International


Here are some of the initial questions I had, (and you may be wondering the same) and some of Maria’s answers. I hope it helps!


What is the Difference between a Glass Kiln and a Ceramic Kiln?

The main difference between a glass kiln and a ceramic kiln is that glass kilns generally heat a single layer from the top and ceramic kilns heat multiple layers from the side.

The reason glass kilns were designed to heat the kiln from the top is because the majority of glass projects tend to be relatively flat. With the heat being radiated from the top, the entire face of the glass “sees” the heat at the same time. This keeps temperature differences within a glass project uniform and prevents cracking.

The same uniform heating results can easily be attained by simply slowing down the firing. Because there are a lot of technicalities, the following resource from Skutt Kilns really breaks this down. It might be helpful to you if you want to learn more – Keep this on file as a resource when you are ready!

screenshot of resource

So now that know I CAN use glass my kiln, what other science is involved that I should be aware of?

Glass expands when heated and contracts when cooled.  The rate that this movement occurs is referred to as the Coefficient of Expansion (COE). The two most common COEs are 90 and 96.  Either coefficient works well in the classroom, but they may not mix or breakage will occur. Sometimes this breakage occurs immediately, and sometimes it occurs in the days or weeks that follow a firing. Either way, mixed COEs create disappointing results.

What if I don’t know the COE of a glass? 

There are 2 options when you don’t know the COE:

  1. Glass is always compatible with itself and may be fused together for tone on tone designs or simple slumped forms.
  2. Use the glass for mosaics. This is a beautiful way to incorporate glass in the classroom for all ages. ( More info on glass mosaics tomorrow…)

How do I prepare the kiln shelf for glass?

Glass will stick to the kiln shelf if there is no barrier between them. Again you have 2 options when protecting the kiln shelf.

  1. Kiln shelf paper can be used to line and protect the shelf.  Some paper is good for multiple firings, while others are single fire use. This option is convenient but more expensive than kiln wash.
  2. Glass kiln wash is specially formulated to easily separate glass from either a shelf or mold. Primo Primer is especially easy to use. It removes from the shelf after firing by simply brushing or by wiping with a damp sponge. No tedious and or messy scraping is required. Primo Primer also retains the fine detail in any mold (i.e., the veins in a butterfly wing.)

See, with a little research and some planning, you can bring the beauty of glass to your art room, even in small ways. Along your journey you may hear some common misconceptions about using glass in the ceramic kilns. Here are a couple of the most common:

Wow- That was a lot of information! I hope it helps you see more possibilities for your art curriculum. If you are like me, it’s worth a little extra research to give students that ‘WOW’ factor with an art project they just can’t get anywhere else in the school. Art wins!

Have you ever tried to use glass or other non-traditional materials in your kiln?

How did it go?

What questions do you still have about using your kiln for glass?

We will do our best to help. 



Jessica Balsley

Jessica Balsley is the Founder and President at AOE. She is passionate about helping art teachers enhance their lives and careers through relevant professional development.


  • Emily

    Great timing! At my new school this year I have a brand-spanking new giant kiln and tons of glass! All of which I’m sure was quite costly. I want to make good use of it since I already have all this glass and tools for it, just don’t know how to do it. I will be reading closely this week. Could you please include some ideas for what types of glass projects I could do?

    • Christina Papanikolaou Erb

      I read somewhere you should fire glass at a cone 06.

      • Carissa

        Depending on what you are doing with the glass, the temperature you fire to will vary. Temperatures range from about 1200 degrees for a tack fuse to 1500 degrees for a full fuse. I use a ramp hold program on my kiln when firing glass and check frequently (with UV glasses through the peep holes) toward the end.

        • Maria

          I am a big fan of tack fusing with frit. It adds a really cool texture. These pieces can always be put back in the kiln for a full fuse to demonstrate how the glass changes at different temperatures.

      • Christina- The information that Ed Hoy’s and Skutt put out should have more detailed specifics on cones. I hope it helps!

      • kathleenmk

        NO that’s around 1848 degrees!

        Glass is fired in the 1100 to 1400 degree range.It depends on what kind of fusing(versus melting) you want.

        • Christina Papanikolaou Erb

          That is just what I read some where. It was a lesson on melting marbles on the bottom of a pinch pot.

    • Emily- Take a look at this article for some tips on glass mosaics!

    • Maria

      Emily, there are a lot of projects that the children can do but the simplest one is to give them a small glass base and have them decorate it with other glass pieces. These can be fused to make pendants or magnets and are super popular. If you are working with younger children you may prefer to have them decorate with glass..

  • Wanda Holmgren

    I used glass marbles (flat bottomed from dollar store) in 2 different projects last year and it worked wonderfully! We just added the marbles to bird baths or koi ponds after glazing and put them in the glaze fire! I wasn’t sure what I was doing, and now know I wasn’t doing it right, but it had such amazing results! I will keep close tabs on your series and try to do it even better this year!

    • Lisa

      I do the same thing! Some of the glass cracked and sometimes they didn’t. Now that I’m thinking of it, the ones that didn’t crack were all on the middle shelves – slower to cool down I’m guessing. Luckily, the students actually liked the cracked look in their birdbaths. Just need to remind them not to run their fingers over the surface so they don’t get nicked!

      • Leah

        My students loved it when theirs cracked too! In fact, they were bummed out if they got a smooth one!!

        • Trish P

          Any chance you could post pics of your final product?

    • Wanda – using glass marbles seems to be a new trend. Thanks for sharing your experiences!

  • kathleenMK

    Good basic info that i had to learn through lots of research with trial and error. Start by flattening bottles for cheese trays. They may need to fire a little longer or hotter than COE 90 or 96

  • Shirley Leslie

    I have an older model ceramic kiln that has dials for heat control which are low med and high. I am wondering if I can use this kiln to fuse and slump glass ? Thanks for any info you can provide .

    • Steph

      I have the same question Shirley. My ceramic kiln has low, medium and high settings. I am also wondering what cone number to use for glass fusing and slumping? I appreciate this article Jessica!

  • Jon

    May i know what’s the temperature for full firing? A glass bottles , flatten and converted into a glass plate. Full Firing/ Half firing.

    Thanks :)

  • Linda Ayling Glozzer

    I just got a kiln that uses cones I was wanting to use for glass and I was told by a friend I couldn’t because you have to go up slow with glass, but reading this makes me think I can use it without converting it over with a controller but still not sure. What do you think?

    • Hi Linda, I’m sorry- I’m no glass expert! I would suggest contacting your kiln manufacturer. Many have great customer support lines with people happy to answer your questions. Best of luck!

    • Stephani Rodgers

      We had the same problem Linda. What I found is we didn’t put a cone in, we just ran the kiln without it. We put ours on high, we have a low, med, and high setting kiln. after three hours we turn the kiln off. I pull our peep hole plugs out after 2 hours and let it cool own another 4 hours. then I prop open the lid and let it cool another 2 hours. all my glass has turned out amazing. Hope this helps.

  • Brooke Wagner

    The “resource” from Skutt is missing.

    • Hi Brooke,

      Thanks for letting us know! It looks like it’s no longer on their website. I found an updated version and linked it!

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