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How to Prime Kiln Shelves

You have questions. I’m here to help!

Some of you are asking great questions about priming a ceramic kiln shelf after viewing my How to Prime a Kiln Shelf Video. I’m happy to expand on my process to help you understand how and why I do things the way I do.

Why we prime.

Hot glass will stick to ceramic and metal surfaces unless the surface is coated with a separator like shelf primer that prevents the glass from sticking.

How and why.

I prime my kiln shelves with 3- 4 even coats of primer after every use. I have a lot of kiln shelves in my studio. A fresh coat of primer will prevent sticking up to 1600 degrees. When I reach for a primed shelf I’m confident I can fire any type of project, using any technique without risk of sticking. For me, it’s an easy extra step I’m willing to take in order to reduce questionable problems.

When and how I remove the used primer on ceramic shelves.

I prime my shelves after every use. If the used primer is in good condition I apply 3-4 coats of fresh primer directly over the used primer. If the used primer shows signs of wear I scrape the old primer off down to the bare ceramic shelf with a razor blade or metal putty knife.

What are signs of wear?

If the old primer looks thin, if it’s chipped or flaking I scrape the shelf down to the bare ceramic and apply 3-4 new coats of shelf primer.

I use Bullseye Shelf Primer. It comes in a powder form that I mix with water following the manufacturers instructions.

The following is an excerpt from my Firing Surfaces sheet.

Firing surfaces have a significant impact on the physical appearance and manufacturing cost of your finished fused glass artwork. In my experience, those two important factors make further study into the best practical uses of the many different options worthwhile. So, let’s get to it.

Ceramic Kiln Shelf: The advantages of using a ceramic kiln shelf are many. A well primed (kiln washed) ceramic self will give the backside of your fused glass a smooth, professional looking finish. Re-priming a ceramic shelf is fast and easy. Plus, doing so makes little dust or mess. (I prime my ceramic shelves with 3- 5 coats of primer before every use.) And using a primed shelf is the least expensive, most cost-effective way to fire glass.

One disadvantage to a using a ceramic shelf is the primer’s dry time. You can speed up the dry time by placing the wet shelf in the sun or by heating it in a vented kiln set to 500 degrees for 15 minutes. (Be sure to let the shelf cool completely before placing any glass on top.) Another drawback is weight. Ceramic shelves are heavy, so moving them in and out of the kiln can be awkward. Size is another thing to consider. Ceramic shelves tend to be cut considerably smaller than the kiln’s interior therefore reducing the number and size or projects you can fire at one time. By cutting a larger, tighter fitting kiln shelf from fiber board, you can increase the number and size of projects that will fit.  

For more information on firing surfaces check out my Firing Surfaces sheet.

Fiber Board as a Kiln Shelf: The fiber board we’re referring to here is a high refractory material purchased at your art glass supplier specifically to use inside a kiln. It’s available in a variety of sizes and thicknesses. The sheets I use are ½ inch thick, 24 inch wide and 36 inch long. This fiber board is primed with 3-5 coats of primer before every use. The pros: it’s lightweight and cuts easily to fit tightly inside any size kiln to maximize the firing space. It becomes smoother with every coat of primer and soon produces a finish that is close to the smoothness of ceramic.

The cons: the porous material retains moisture like a sponge, therefore its flimsy when wet with primer (so moving it when wet is not recommended) and it takes longer to dry than ceramic.

White glass, and some paint-based labels like those on the backside of Grey Goose bottles, will stick to the board even if it’s well primed. Removing white based projects will pull a chunk out of the board. I fire these projects on fiber paper or primed ceramic to avoid damaging my fiber board shelves. 

Fiber board is soft. Dropping glass or another hard object on the shelf will put a hole in the smooth surface. The upside is damaged shelves can be cut down and used for shelves in smaller kilns. Or they can be cut into strips and used to dam cast glass projects. Nothing goes to waste.

For more information on Kiln Shelves and Shelf Primer check out my Glass Fusing Terms sheet.

Kiln Shelf: A ceramic or fiber board shelf that supports the glass while firing. A primer or separator must be applied to the shelf before firing to keep the glass from sticking to the shelf. See shelf primer. 

Kiln Wash: See shelf primer.

Shelf Primer: A powder mixed with water and “painted” on the kiln shelf and slumping molds before use to act as a release and prevent the glass from sticking.

Thank you for all your positive feedback! I hope you find this new information helpful!

Where ever you are in your journey you are doing great! Keep the fire burning!

Happy Fusing!


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2 thoughts on “How to Prime Kiln Shelves

  1. Hi Lisa! I was wondering if you have problems with shelf primer sticking to your glass and if opals are worse in this regard than transparents? Thank you for all the info you give!

    1. Primer will frequently stick to white glass and when the glass is heated above fusing temperature of 1,465F; Like when your combing glass. You can remove it with a single edge blade or you can use bathroom cleaners that help remove calcium build up.

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