Keep in mind that glazes and clay bodies must be matched for temperature maturation as closely as possible. In nearly all circumstances, low-fire clay bodies should be used with low-fire glazes. Mid-range or high-fire clay bodies will remain too porous or “punky” if combined with the wrong type of glaze. The wrong glaze also can have an undesirable effect on the color of the finished piece. When bisque firing low-fire clay bodies, you can fire the clay slightly higher than the glaze. Usually, this means you will bisque fire to cone 04 (make sure you get the zero in there!), which will tighten the clay body just a bit more than a lower temperature will. After bisque firing is complete, the clay contains no chemically bonded water. Remember to use wax resist and coat the pot’s bottom and up its outer sides 1/4 inch before using underglazes and glazes. Wax resist prevents the pot from sticking to the bottom of the kiln, which can crack the pot or ruin the kiln shelf. Raw glazes are not at all the same color they will be once fired, which can stretch your imagination as you work to envision what the finished piece might look like. If you have examples of the fired glazes, you can use them for reference as you glaze your new pots. It’s important to note that raw firing is not as robust as glaze firing and is best suited to decorative pieces because it is not food-safe. The firing schedule for glazing is faster than for bisqueing. This is because the bisque firing has already transformed the clay into a ceramic material. Low-fire glaze firings are usually between cone 06 and 04, with cone 05 being very common. A typical firing schedule includes:
Two hours with ramp at 150 degrees F/hrThree hours with ramp at 400 F/hrRamp at 120 F until the desired temperature is reached
Allow the kiln to cool down at its own pace until it is below 200 F. At that point, the kiln can be opened, and your new, finished pottery can be unloaded.
