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Common Questions » FAQs

About firing your kiln.

How long do I need to let my students work dry before I bisque fire it?

Answer: Let the work dry until it is bone dry. That is, when the piece no longer feels cool, but rather feels room temperature, because the moisture left in clay will always make the clay feel “cool”. The time it takes to let clay dry varies with the weather and environment where you are working. You will notice your work dry faster on the hot dry summer days and slower during the raining season. Most pieces can dry completely when left uncovered for three to four days.

What is the best temperature to bisque fire to?

Answer: Bisque firing is generally fired between cone 06 to cone 04. Cone 04 is the temperature I most recommend, especially when firing earthenware clay. Firing to cone 04 (the hottest of the temperatures mentioned) allows the impurities in the clay to burn out, preventing problems later on in your glaze firing. If the impurities in the clay do not burn out in the bisque they can later burn out in the glaze firing causing pin holing or crazing in your glazes.


Do I need to bisque fire stoneware clay at a different temperature than earthenware clay?

Answer: No. All clay can be bisque fired to the same temperature and even in the same kiln. Bisque firing is simply the process of hardening the clay so that the piece is less fragile and can be glazed easier, with less chance of glaze defects.


How often do I need to put kiln wash on my shelves?

Answer: Kiln wash should always be applied to new shelves. After the initial coat you simply need to up keep your shelves. Grind or scrap off any glaze drippings that occur after your firings and coat the area with new kiln wash. If you find that your shelves are beginning to look as though the kiln wash is thin apply a new coat of fresh kiln wash.


How thick is too thick in the walls of my clay projects?

Answer: The problem with thick walls in clay projects is that it takes longer to dry. When a piece is not completely dry and is put into the bisque kiln it will most likely explode and/or crack. Water (or the moisture in the clay) when heated will expand and turn into vapor, causing the piece to make way for the expansion of the moisture and explode. When possible hollow out pieces that are solid. This makes the object lighter and safer! Any piece greater than ¾” – 1 ½” thick in any area is a candidate for explosion if it is not dried carefully.

When loading the kiln, can the pieces touch one another during the firing?

Answer: Pieces can touch each other and be stacked carefully in the bisque firing only. During the glaze firing, the actual glaze on the pieces will become molten and can run into one another if the pieces are touching in the kiln. When loading a glaze kiln it is wise to place the pieces a fingers width apart to prevent glaze disasters.


How soon can I open the kiln after the firing is complete?

Answer: If you have a pyrometer on your kiln to tell you the inside temperature of the kiln, you can easily know when the kiln has cooled off completely. It is recommended not to open your kiln until it has cooled to 100 degrees Fahrenheit or cooler. It is important to remember to never open your kiln while it is still on or glowing inside. The internal temperature of a kiln can reach very dangerous temperatures that can cause tremendous harm if exposed. If you do not have a pyrometer on your kiln, it is good measure to wait at least a day before opening your kiln.