Maintaining your kiln furniture is one of those most overlooked but important aspects to ensuring the longevity of your kiln. It also ensures that your production runs smoothly. While it’s tempting to ignore the shelves inside of your kiln it will catch up to you eventually and end in a ruined product.
The easiest way to prevent glaze build-up is to regularly clean your shelves to apply kiln wash. You might be thinking, another thing to add to my list of consumables. Luckily, kiln wash can be made in your factory or studio at little cost to you; we’ll share the recipe below. First, let’s dive into everything you need to know about kiln wash and how it serves to keep your kiln healthy and productive.
We like to compare kiln wash to the non-stick coating on your favorite pan at home. Its sole purpose is to act as a barrier between your kiln shelf and the ceramic and ceramic glaze that sits on top of it. As you may already know, glaze drip is a pervasive and problematic issue and once it’s started sticking to the kiln it’s impossible to remove without grinding it away. If left unchecked, it will eventually create an unstable surface for your ceramics to sit on. To put it simply, it’s better to keep it off the shelf, when possible. Kiln wash does exactly that.
There are three primary properties to kiln wash: alumina hydrate, kaolin, and water. The alumina hydrate and kaolin are mixed with water in a 50/50 ratio until the mixture resembles half and half or skim milk. Depending on your operating temperature you may want to research washes that observe a higher thermal resistance but Alumina is the go-to ceramic hydrate.
Mixed kiln wash will resemble a thin white fluid and act, in many ways, like the glaze you put on your ceramics. As we mentioned earlier, it should resemble half in half or skim milk when mixed at the proper ratio.
Once your wash has been mixed, it needs to be applied to your shelves in 2-3 coats. Wash can be applied using a conventional paintbrush, paint roller, or even a paint sprayer. As each coat is applied, allow it to dry before applying the next coat.
As kiln wash is continually fired it will eventually flake off of your shelf, which is why we recommend that you leave a ½” edge on the front of your shelf that is without wash to keep those flakes from adhering to your ceramics.
Many kiln operators will forgo mixing their own recipe and just buy a pre-mixed kiln wash off the shelf. However, for smaller operations, it's entirely possible to mix your own wash. After all, some of us like to roll up our sleeves. This is a basic kiln wash recipe that we recommend for most kilns:
10% ball clay
50% alumina hydrate
Mix these powders with the same volume of water to create a 50/50 mixture of powder and water. Vigorously mix the solution until it reaches a thin, creamy consistency. From there, apply the kiln wash using a paintbrush, roller, or sprayer.
If you periodically flip your shelves you can skip the ball clay and use a ratio of 10% kaolin and 90% alumina hydrate mixed with the same 50/50 ratio of water. There are many recipes online, some including things like salt soda and other materials that can bolster the thermal properties already inherent in the wash.
Like the natural process of glaze run, kiln wash can also build up, flake away, and affect the overall levelness of your shelves as it's fired over and over. Once your kiln wash has become uneven it's time to remove it and re-apply it. The primary means for removing kiln wash is by grinding it away. If you've ever used an angle grinder, then you know it's a great tool for grinding away at a surface. An angle grinder can make quick work of the leftover kiln wash on the surface of your kiln shelves. With some skill, it can also have a surprising degree of accuracy. However, the type of disc you use depends on the amount of kiln wash you're dealing with.
Fiberglass discs are great for regular use when your primary intention is to remove a small amount of kiln wash from your shelf without actually grinding away at the shelf itself. We recommend these for frequent, light grinding.
Sometimes kiln wash is so pervasive that it requires you to level the entire shelf along with the wash. A diamond cup wheel will make quick work of the kiln wash and grind into the shelf itself, giving you the power to re-level the entire shelf. However, be aware that using such a hard material as a grinding agent can lead to irreversible damage to your shelf if you're too heavy-handed.
Much like a diamond cup wheel, silicon carbide cup wheels are for heavy-duty grinding and resurfacing of your shelf. In all intents and purposes, a silicon carbide cup wheel is indistinguishable from a diamond cup wheel.
If kiln wash is the nonstick coating on your sauté pan, then kiln paper is the kiln-equivalent to the parchment paper you place on your favorite roasting pan. This analogy works on many layers; just as a non-stick pan coating is more durable than parchment paper, so too is kiln wash when compared to kiln paper.
However, both serve their purposes. Kiln paper is a simple, elegant solution to creating a protective barrier in kilns that fire at a temperature at or below 1,600F. Best of all, they are easily disposed of and re-applied when compared to kiln wash.
While kiln wash is a simpler product it simply does not compete with the high melting point and longevity of kiln wash. To break it down easily; use kiln wash if you need something that stays put for dozens of firings under high heat. Use kiln paper when you have a smaller studio with less frequent firings at low temperatures. One other caveat to mention is that, if applied excessively, kiln wash can ruin your electric kilns so apply it conservatively or use kiln paper.