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You may have heard of kiln cookies and wondered what they are and what they do. This post is all about the humble kiln cookie. Also known as patties, the kiln cookie is firing essential and handy kiln saver. Once you start using them, you won’t look back!
Kiln cookies are thin flat slabs or discs of clay that are placed under your pottery during a glaze fire. Most potters bisque fire them before they are used. Others use bone dry clay but make sure it’s thin enough that it does not explode in the glaze fire.
What are Kiln Cookies and Why Use Them?
Kiln cookies are used for two main reasons:
- To catch any drips of glaze that may have run down your pottery in a glaze fire. Glaze can run because it has been applied too thickly, or too close to the base of your ware. Some glazes, called flowing glazes, simply move about more than other glazes that stay put.
Whatever the reason, it’s annoying if your glaze drips down from your pot onto your kiln shelf. Most of the time if you get glaze on the kiln shelf, you can snap the pot off by wiggling it. But, even if you can remove the pot easily enough, you will need to grind the glaze off the shelf.
Kiln cookies catch the glaze and stop it from going onto the shelf. Of course, if your glaze drips onto the cookie, then the cookie will be stuck to your pot. You then have the problem of removing the cookie. But this is an easier issue to deal with than having the pot welded to the shelf.
- Kiln cookies can also be used under large flat pieces of pottery as they fire. Big flat items like platters, plates, and tiles have a tendency to bend or warp when they are fired. This is because there is a lot of internal tension in large flat surface areas as they fire. Sometimes pieces will break under the tension.
Placing a cookie under a plate or a similar item help with heat distribution during firing. The cookie acts as a buffer between the plate and the kiln shelf. If anything breaks or warps, it is likely to be the kiln cookie rather than your pottery.
Here are some kiln cookies in action…
How do you Make Kiln Cookies?
There are different ways to make kiln cookies. Whichever technique you choose they are pretty simple to make.
Here are some methods:
- Pressing them out with the palm of your hand.
- Rolling out a slab with a rolling pin.
- Throwing the clay at your wedging table at an angle. This spreads the clay out across the surface of the table into a thin patty.
- Throwing them on the wheel.
You can either make them into the size that you need or cut them to size with a knife. It’s important that the kiln cookie is larger than the base of the piece that will sit on them. As a rule, make the patty ¾ of an inch larger than your pottery. This should be enough to catch any running glaze.
Because kiln cookies are thin and flat, they have a tendency to bend as they dry. If you find this is happening, you can dry them sandwiched between two surfaces. For example, you can dry them between a couple of wheel batts, or even under a book.
I dry mine as I would a tile of clay, by putting them on a baker’s cooling tray. I then wrap it loosely in a bag so that they don’t dry too quickly. This is enough to let them dry without bending.
It’s important that the kiln cookie isn’t bent because it needs to be stable enough to support your pottery.
You can also paint the cookie with kiln wash. If you use kiln wash, and your glaze does drip, the pot is much easier to remove from the patty.
Do you Need to Bisque Fire a Kiln Cookie?
It’s quite common practice to bisque fire kiln cookies before they are used. You can just put them in with a bisque load, rather than firing the kiln for them specifically.
However, not all potter’s bisque fire kiln cookies first. Some potters simply make sure they are bone dry before being placed under the pottery for a glaze fire.
If you choose not to bisque fire the cookie, you need to make sure that it is really quite thin. This leads me to the next question about kiln cookies…
How Thick or Large Should Kiln Cookies Be?
There are different variations in the way kiln cookies are made. I will go into these differences a little further down. However, for the most part, kiln cookies are about ¾ of an inch larger than the pottery resting on them.
Nevertheless, it’s important that they are not so large that they take up too much space in your kiln.
With regards to thickness, potters will often make their kiln cookies between 1/8 -1/4 inch thick. 1/8 of an inch is often recommended. However, the thickness does depend on whether you are bisque firing them first.
If you are bisque firing them, you can get away with them being a bit thicker. About the thickness of a pancake is ok. But if you are putting them in bone dry, make them as thin as you can without making them fragile.
How Many Times Can You Use Kiln Cookies?
Kiln cookies are quite fragile. Because they are thin and flat, they break easily. But I find that I can use them a few times before they become too brittle.
Some potters report that they can use their kiln cookies time after time. But it’s common for them to bloat up after they have been through a glaze fire a few times.
How many times you can use them depends a little on the type of clay you use. That leads me neatly onto the next question….
What Type of Clay to Use to Make Kiln Cookies?
Most potters will make their kiln cookies out of scraps of recycled clay that they have lying around the studio.
However, the patty does need to be the same cone or higher than the clay you are glazing. If you use a lower cone, there is a risk it will melt, warp or bloat during the glaze fire.
Some potters recommend making kiln cookies out of cone 10 clay to make sure they are as robust as possible.
Other potters get a bit more technical and have a kiln cookie recipe.
One such recipe is to mix EPK Kaolin with Alumina Hydrate. Alumina Hydrate is refractory, which means that it is heat resistant. As such, it doesn’t melt to your pottery. EPK helps to bond the alumina hydrate together and makes it into a workable mix that you can shape.
Another recipe is to mix grog, fire clay, or alumina with a high-temperature clay. This recipe is also designed to make kiln cookies that are refractory and can survive multiple firings.
Different Varieties of Kiln Cookie
Usually, when potters talk about kiln cookies, they are talking about the large, thin, flat patties described above. However, there are different types of kiln cookies. Here are some variations on the theme:
Small Kiln Cookies
These disks have 3 or 4 little raised bumps on the surface. The pot sits on the raised bumps. And the pottery can be kept steady on the small cookie by using a small amount of Elmer’s glue. Alternatively, you can use tacky wax to keep the cookie attached to the pot. The glue or wax will burn off as it fires.
Be aware that as your pot fires it will shrink a little. If the cookie shrinks less than the pot, it can get wedged in the foot ring. This is because the foot ring shrinks around the cookie and traps it.
An alternative to using a kiln cookie is to use wadding. Wadding is normally made from a mixture of alumina hydrate and EPK. It is then rolled into small balls, beads of blobs about the size of a pea. 3 or 4 balls of wadding are stuck to the foot ring of your pot using a dab of glue. Once the pottery has been glaze fired, these dots of wadding tap off the foot ring easily.
The balls of wadding can be stuck to the foot ring when they are workable. These are then left until they are air dry. They are small enough that they are very unlikely to crack or explode during the glaze fire.
Alternatively, some potters will make a slab of wadding and cut it into little cubes. These are then bisque fired and placed under the pots during a glaze fire. They work a bit like kiln stilts.
Wadding is often used in atmospheric firings like soda firing or wood firing. The wadding raises the base of the pottery of the kiln shelf. This allows flashing, characteristic of atmospheric firing methods, to occur all the way around the piece, including the base.
How to Remove Kiln Cookies that are Stuck to a Glazed Pot
If your glaze does run, you will need to find a way of removing the pot from the kiln cookie.
There are a few ways of doing this:
- TAP IT: If the glaze has only run a little, you may be able to simply tap the cookie off the pot.
- SAND IT: If the glaze has run more substantially, you might have to chisel the cookie off. You will probably have to do a bit of sanding if this is the case. You can either use sanding paper or a palm sander. If you are sanding or grinding, remember to wear a mask.
- GRIND IT: Another option is to grind the kiln cookie off the pot. You can either use a Dremel tool or a grinder. Diamond Core Tools grinders are disks that are attached to a batt on your wheel head. As they turn, you hold the pot over the grinder, and it will grind the cookie off evenly.
- Check out this video to see Diamond Core Tools being used
Kiln cookies are a simple but useful part of your pottery arsenal. Experiment with what works for you, and you will avoid hours of grinding glaze off your kiln shelves.