Frequently Asked Questions About Ceramic Firing and Techniques

These answers and tips are recommendations based on my own long-term practical experience—I have been running both low-fire and high-fire firings in my home studio for at least ten years. These are not official textbook or professional guidelines, but rather observations that I have found to be good and functional in practice along the way!

Please note, however, that if you intend to make food-safe dinnerware, you must always follow the official guidelines and manufacturers' specifications regarding clays, glazes, and firing temperatures.

 

1. Can high-fire clay be used in a low-fire setting (e.g., with low-fire glazes)?

Yes, it can, as long as the piece is intended for decorative or dry storage use.

As the name implies, the primary purpose of high-fire clay is to be fired at high temperatures, which causes the clay to vitrify into fully dense stoneware. If high-fire clay is fired at a lower temperature, it won't become stoneware; instead, it remains technically a bit more porous.

In practice, however, the piece will become completely hard and durable—it certainly won't crumble or be full of holes. It is perfectly suitable for normal everyday use as a tealight holder, pen cup, or other decorative display. The only difference from high-firing is that the material is not completely waterproof. Therefore, this combination will likely not hold standing water (such as in a flower vase) and is not suitable for dinnerware, but for any other decorative or interior use, it is excellent.

 

2. Can pieces be single-fired (once-fired, i.e., glazing raw clay and firing only once)?

Yes, they can. Single-firing is a fully functional technique used by many ceramicists and hobbyists. In single-firing, the piece is glazed while it is still raw, skipping the separate bisque firing stage, and goes straight into the glaze fire.

If you want to try this technique, keep the following things in mind:

  • The piece must be 100% bone-dry: Since no bisque firing has been done, even a tiny amount of residual moisture in the clay can cause the piece to shatter in the kiln.
  • Glaze behavior: The glaze might not always look exactly the same when brushed onto raw clay and fired as it would in a traditional two-firing process.
  • Fragility: Raw clay pieces are extremely fragile, so you have to be very careful when applying the glaze. Many potters (including myself) often avoid single-firing simply because the risk of the piece breaking before the kiln or during the firing is higher than with two separate firings.

 

3. Can the bottom of a piece be glazed?

Yes, it can. It is technically not impossible at all, even though many firing services ban it to protect their kiln shelves. There are two common ways to glaze the bottom of a piece:

  • Fully glazed bottom (Stilts): The piece can be placed in the kiln on special pointed supports called stilts. After firing, the stilts will leave tiny, sharp pinmarks in the glaze surface. This is completely normal, and they can be easily filed smooth with a standard small hand file. With this technique, the piece must be well supported (at least 3 points, and for larger pieces, also in the middle and ends) so that the bottom doesn't sag or warp in the high heat. This method is best suited for small and medium-sized works.
  • Partially glazed bottom (Foot ring tools): Nowadays, many handy foot ring tools have come onto the market, allowing you to glaze the bottom partially. These tools make it easy to wipe or mask the glaze very neatly off just the specific part (like a raised ring) that touches the kiln shelf. This allows the piece to sit securely on its own foot in the kiln without extra stilts, while the center of the bottom still gets a beautiful glaze finish.

 

4. Do clay pieces always need to be covered with plastic to dry as slowly as possible?

No, absolutely not. Using plastic depends entirely on the size and thickness of the piece. Being overly cautious with plastic often just means waiting weeks for no reason.

  • Small and thin works (under 5 mm): Standard or small, thin pieces usually don't need to be covered with plastic at all. They dry safely and much faster in the open air.
  • Large, flat items (such as plates): Even large plates don't need to be covered with plastic, as long as you protect their shape correctly. As they dry, the edges of a plate often tend to warp upwards, which is why it's recommended to place a heavy board (like a plaster or wooden board) on top of the piece. The most important thing is that at least the surface underneath is breathable so that air can circulate and drying doesn't take forever. For this you can use a lot things from oven racks to small drying racks designed specifically for small items.
  • Large and thick works (over 5 mm): In these cases, covering with plastic or slowing down the drying process is justified. If a massive or very thick piece dries too quickly, different parts of the clay dry at different rates, causing tension that easily leads to cracking.

 

5. How should jewelry and other small items be fired and glazed? (Many have pre-made holes or hooks for hanging)

It is completely possible and highly recommended, as long as you use the right tools. You don't need to try and balance tiny jewelry pieces on a flat kiln shelf; instead, there are specific techniques designed just for them:

  • Jewelry holders and support rods: You can string the jewelry pieces through their holes to hang from specialized firing racks or support rods. When purchasing racks and rods, it is crucial to ensure that they can withstand the specific firing temperature (low-fire/high-fire) you intend to use. If you are doing a high-fire, the rack and rods must be rated for high temperatures.
  • Mind the weight and rod thickness: The heavier the piece, the sturdier and thicker the rod needs to be. Metal rods, in particular, can easily warp or sag under too much weight in the intense heat of the kiln, which can cause the pieces to slide into each other or onto the kiln shelf.
  • Glazing the entire piece: The biggest advantage of using rods is that you can glaze the jewelry piece completely on all sides, as it only touches the rod from the inside of the hole.
  • Small items and kanthal wire: If the pieces are very small, it can be difficult to make holes large enough to keep the glaze from clogging them. In these cases, it is recommended to use kanthal wire (high-temperature resistance wire) to cut and shape your own small hanging hooks before firing. You can also find pre-made hanging hooks on the market—just be sure to check whether they are rated for low or high-fire when buying.