Are you new to pottery and wondering what kiln wash is and how it is supposed to be used? If you are, then we are here to help.
In this article, we will explain what kiln wash is, why you should use it, when not to apply it, and how to make it, and cover a variety of other questions you may have about using kiln wash.
What is Kiln Wash?
Kiln Wash, sometimes referred to as shelf primer, are liquids that you apply to a kiln shelf to prevent clay and glaze drips from sticking to them. Brushing kiln wash on your kiln shelves creates a protective layer, much like greasing and flouring a pan does before baking.
Kiln washes are made from refractory materials such as silica, alumina, or zirconium that have high melting points. Their exact formulation can vary greatly depending on the firing range of their intended use. They should always be
What is Kiln Wash Made Of
Typically, silica is the primary ingredient used in kiln wash intended to be used at low- and mid-cone ranges (1745℉ (950℃) and 2012℉ (1100℃), Cone 015 up to Cone 1). Alumina, sourced from kaolin clay, is used as temperatures approach the upper limits of mid-fired clay and the lower end of high-fire (2124℉ (1240℃) to 2381℉ (1305℃)).
Zirconium, in the form of zirconium silicate or zirconium oxide, is reserved for high-fire work due to its higher melting point of 3371℉ (1855℃) and its expense. Zirconium-based kiln wash is quite a bit more expensive than other types of kiln wash.
Of course, higher temperature kiln wash can be used for lower temperature firings, but most serious potters keep all three on hand to minimize expenses.
Buying Kiln Wash
Kiln washes can be purchased either in powder form, which requires hydrating, or pre-mixed. While the powders are less expensive, many potters still opt to buy pre-mixed kiln wash as its convenience and consistency of results are seen as worth the minimal extra expense.
You can also make your own kiln wash. This is a subject that we will cover in-depth in a subsequent section.
Why Do You Need to Use Kiln Wash?
The simple answer to why you need to use kiln wash is to protect your kiln furniture from damage. Kiln shelves are usually made of ceramic materials, just like your pottery. If glaze comes into contact with your ceramic shelves, it will stick and cook onto them.
To prevent unexpected glaze runs from ruining your ceramic shelves, you coat them with a good kiln wash. This doesn’t mean you shouldn’t still use stilting to help prevent contact between your pieces and the shelf. It is just an extra measure to help ensure your work and kiln furniture do not come into direct contact.
Beyond the worry that glaze drips and spits can cause, there are times when bloating or melting clay bodies can occur from accidental over-firing. If this happens or a piece should topple over, you have a real problem if you haven’t used kiln wash. With some porcelain clays, they don’t even have to fall. The clay itself can bond to the shelf.
Not only will you be faced with your work being ruined, but you will also have a good deal of work ahead of you. You will first have the difficult task of removing the fused-on glazed pots, and then you will need to grind and sand the residue off of the kiln shelves.
This is an impossible task to perform without damaging the kiln shelves. Even worse is the fact that any glaze that you miss or that has seeped into the pores of the shelf will continue to eat away with every subsequent firing and considerably shorten the life of your kiln shelves.
Applying a thin layer of wash to your kiln shelf prevents this from occurring. Considering the possible ramifications, the minimal time and expense of using a thin coat of kiln wash for all glaze firings are more than warranted.
Kiln Wash Recipe
There are many kiln wash recipes that can be used, and the one that works best will depend on the firing range that you are working in.
Commercial Powdered Kiln Wash
If you have purchased kiln walls from a supplier in powder form, be sure that it is rated for the firing range you will be working with and mix with water according to the manufacturer’s directions.
Making your Own Kiln Wash
If you are wanting to make your own kiln wash, then it is a good idea to formulate it for minimum shrinkage. Kiln wash shrinkage during firing is what causes flaky kiln wash.
Flaky kiln wash is messy, and has to be reapplied often, and in a worst-case scenario, kiln wash flakes can fall on your pottery and ruin your work.
Another thing you want to avoid is kiln wash which is hard to remove from your kiln shelves. This can occur if you add fluxes like soda or salts. So try to avoid them. It can also be an issue if you are firing in a flux-filled kiln like soda, wood, or salt firings.
Ideally, your kiln wash sticks well to the kiln shelf until you are ready to remove it. Then it will come off easily using a paint scraper.
KIln Wash Recipe
Here is a simple kiln wash recipe that we have found works well for most firings short of cone 10. For extremely hot firings, we will use pure alumina as a kiln wash to make sure and preserve the health of our kiln shelves.
This formula has extremely low shrinkage to avoid kiln wash flakes, applies smoothly, and, just as importantly, is easy to remove.
What You Will Need
This kiln wash requires only three ingredients, all of which should be readily available from your local pottery shop and most online glaze suppliers.
Alumina – The primary ingredient that makes your wash work; highly refractory, expensive, powdery, doesn’t melt, and doesn’t shrink.
EPK – Edgar Plastic Kaolin bonds the other ingredients together; highly refractory, cheap, doesn’t melt and has high shrinkage.
Silica – Used primarily as an expander to reduce the cost of your kiln wash; highly refractory, very cheap, can melt if it comes into contact with fluxes, and has low shrinkage.
Water – Used to hydrate and thin your kiln wash.
Epsom’s Salts (optional) – Used as a flocculent to thicken your kiln wash and make it more spreadable. You can simply leave your kiln wash thicker, but this increases the cost of use.
Please note: The quality of ingredients can vary widely from one supplier to another. If you suffer excessive flaking, crawling, or cracking, substitute half of the EPK used with calcined kaolin. It is more expensive but has a lower shrinkage rate.
MIxing home-made Kiln wash
We will give our recipe in parts just to make it simpler to create whatever amount of kiln wash you may need. We use coffee scoops, but it doesn’t really matter what measuring device you use. For small batches, a teaspoon will work, and for more kiln wash, you could use a mug. Just maintain the correct rations.
- 2 parts Alumina Hydrate
- 2 parts Edgar Plastic Kaolin
- 1 part Silica
For the sake of safety and to protect your lungs, it is always an excellent idea to wear a dust mask when mixing kiln wash. We also recommend wearing gloves and safety goggles. These ingredients come in a powdered form and can create a lot of airborne dust.
Combine all of your dry ingredients in a sufficiently large bowl or bucket. You will need plenty of room to add water.
Work the ingredients together with a spoon, fork, or your fingers. The best method will depend on the volume you are mixing. Our personal preference is to use our fingers.
Slowly add water to create a doughy consistency, and then continue adding and using your mixer to blend the water in. We most often use a stick blender and add healthy dollops of water at a time.
You can continue this process until you achieve your desired thickness or proceed as follows.
Your kiln wash should be the consistency of melted ice cream or half and half.
Continue thinning your kiln wash until it is as thin as milk.
Then add Ebsom’s Salt to cause the particles of the mixture to come together.
Run this through a strainer to remove any lumps, and you’re done.
The advantage of this process is the kiln wash will flow easier, dry slower, and make it simpler to achieve a smooth coat.
How to Use Kiln Wash
Kiln wash application is a fairly simple process. To begin with, if you have brand new kiln shelves, you should put them through a low-fire firing in your kiln before applying kiln wash. This is to eliminate any leftover moisture that may be hiding inside of them them.
Moisture hiding deep in a kiln shelf can lead to warping and cracking.
When your kiln shelves are dry and cool, lay them out on a smooth surface and wipe them with a large wet sponge and allow them to air dry.
Once dry, coat each kiln shelf with a thin layer of kiln wash. Apply kiln wash using long flowing strokes in a single direction. Thin coats work best.
You want complete coverage, but try to avoid getting kiln wash on the edges of your kiln shelves. It can flake over time and drop onto works being fired nearer to the kiln floor.
Remember, a thin coat is best; more isn’t necessarily better.
Allow each kiln shelf to dry for several hours.
Turn your kiln shelf to ninety degrees and repeat the above process. You should be working across any brush marks left by the previous coat of kiln wash. Again, less is more.
Allow the second coat of kiln wash to dry for an hour or more, and they will be ready to use.
When to NOT Use Kiln Wash
As important as the kiln wash rules are, they are not universal. There are times when it is entirely appropriate not to use kiln wash and on certain types of kiln shelves, you should not apply kiln wash to for any reason.
Kiln Fiber Shelves
If you have fiber shelves, they should never be coated with kiln wash. Fiber shelves, most often seen in glass kilns, are absorbent by nature, and applying kiln wash would destroy them. They are designed for a low-moister atmosphere and will unravel if wet.
If you need a barrier to prevent sticking with fiber shelves, we recommend using kiln shelf paper.
Nitride Bonded Silicon Carbide Shelves
As a general rule, glazes will not stick to nitride-bonded silicon carbide shelves. Because of this, it is normally not necessary to apply kiln wash to them. The one possible exception is when firing certain types of kaolin clays that can become molten under proper conditions and bond with the kiln shelf.
In these cases, kiln wash saves the kiln shelves from permanently damage.
When Bisque Firing
Also, there is no need to use kiln wash when performing bisque firings. As you are probably aware, bisque firings are raw clays and do not involve the use of glazes. So there is no need to prevent glaze drips from damaging your shelves.
If you are concerned about specific clays becoming permanently fused to your kiln shelves, then kiln shelf paper works just as well as kiln wash at the modest temperatures used for bisque firings.
Here we offer a few extra tips that have not been covered in the article so far. While they haven’t fit into any of the sections above, the information listed here is no less important.
Kiln Wash the Floor of Your Kiln
Just as glazes can spit and run onto a kiln shelf, they can also drip onto the floor of your kiln and damage the fire bricks. To prevent this from happening, it is advised to coat your kiln’s floor with kiln wash periodically as part of its regular maintenance.
Avoid Your Kiln’s Heating Elements
You should do your best to avoid kiln wash from making contact with the heating elements inside your kiln. It will attack the materials they are made from and cause them to burn out fairly quickly. If your kiln floor has heating elements, do not apply kiln wash to them.
This type of degradation is true of both wet and dry kiln wash. This is one reason we recommend vacuuming your kiln in between firings. Making sure the resistance coils in your kiln remain free of wash flakes and dust will greatly increase their service life.
Salt or Soda Glazing
Salt and Soda glazing are often used in the production of traditional earthenware and low-fired stoneware. These processes involve creating an atmosphere that is rich in flux materials within the kiln.
The silica that is used in the majority of kiln wash formulations can react with these flux materials and become glaze themselves. Avoid using kiln washes that contain silica when performing these types of firings. If you are worried about wares bonding to shelving, use wading to raise them off the shelves.
Fine Art and Glasswares
If you are working with glass that may show brush strokes and imperfection through their transparent bodies, it is recommended that you use kiln shelf paper instead of kiln wash. It is much smoother in nature.
The same advice would apply to fine artwork ceramics, where imperfections, even in the bottom of a piece, would be considered a flaw.
Kiln shelf paper is considerably more expensive than kiln wash, but in these cases, it is warranted.
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Frequently Asked Questions
Should I kiln wash the floor of my kiln?
It is generally recommended that you do a kiln wash on the floor of your kiln. The one exception to this advice is when there are resistance coils embedded in the kiln floor. You should always do your best to avoid having kiln wash, both dry and wet, and contact your heating elements.
Frequent vacuuming of your kiln and wiping your coils down with a damp sponge will help extend their service life.
Is batt wash the same as kiln wash?
In pottery circles, any flat surface is generally called a batt. Kiln wash is considered a more American term, while batt wash or shelf primer is most often used in Europe and the U.K. So, yes, they are the same thing.
How do you get kiln wash-off pottery?
If kiln wash flakes have gotten onto your pottery during glaze firing, then there is little you can do other than start over.
In some very rare events, it may be worthwhile to try and sand and polish out the imperfection, but as a general rule, it is easier just to create a new piece and clean your kiln before firing it.
Can kiln wash be too thick?
Yes, kiln wash can be too thick. If it has too heavy a consistency when applied or too many coats are laid on, it can lead to cracking and peeling.
Do I have to use kiln wash for bisque firing?
In most cases, kiln wash is not considered necessary during bisque firing. That said, it does not present any danger either. Unless you are using nitride-bonded silicon carbide shelves or fiber kiln shelves, it is always a good idea to keep kiln wash on any kiln shelf you have in your shop.
How long does kiln wash need to dry?
It is recommended that you wait at least an hour between applying kiln wash coats to a shelf. Most artists use two or three coats on each shelf, allowing the last coat to dry for several hours.
Some potters will even put a kiln shelf through a low bisque firing for good measure. This can be a good idea if firing glazes that are sensitive to moister.
What is the ratio of water to kiln wash?
The exact proportions of kiln wash powder to water will depend on the exact formulation of the kiln wash. Water should be added and well mixed in until the kiln wash is the consistency of whole milk or half and half.
It is better to err on the side of being thin and needing to apply extra coats than to have the kiln wash too thick. Kiln wash that is too thick can lead to cracking and peeling.
I’m Jessica and I’m obsessed with kilns. I’ve been doing pottery from when I was a little girl and I created TypesOfKilns to help people find the right kiln for their needs.