Having trouble firing a sitter/timer kiln? Not sure when to plug your peepholes? Click here for a handy firing chart.
BISQUE
Q: I've noticed you recommend a cone 04 bisque for your clays. Why? Typically bisque firing is done from cones 06-04. With lighter-colored clays or very thin pieces-cone 06 can be fine. But if you are using a darker or speckled clay, or your pieces are thicker or have variation throughout-cone 04 will produce more consistent results. Darker and speckled clays are "gassy," and need a little more heat in the kiln. Otherwise, occasional blisters will result after glaze firing (bubbles in your clay that can interfere with the look and functionality of your piece). A cone 04 bisque firing also allows the clay to be at a great stage of vitrification for glazing-allowing glaze application to be smoother and more even. We always recommend cone 04 bisque for all of our clays, and a slow setting on digital kilns for both the bisque and glaze firing.
Q: My pots keep blowing up during the bisque firing. Why? Usually this is a simple answer-they're not dry. Clay must be 100% dry to fire properly, otherwise the water in the pot turns into steam. This can often result in "blow-outs," often seen in the bottom half of heavy pots or in thicker pieces and sculptures. When in doubt-give your pieces an extra day to dry. And always keep in mind-if you are storing your greenware in a really humid environment, dry pieces can re-hydrate and take on moisture from the air. they can also dry incredibly slowly. When firing thick pieces or large sculptures, even if you are sure they are dry, it won't hurt to program a 2-hour preheat for your firing (leave the peephole plugs out). This let the kiln heat up more slowly. If you touch the bottom of your greenware and it feels really cool to the touch, the clay is probably still wet.
GLAZE
Q: When I take my pieces out of the kiln after glaze firing, I often hear "pinging" in the glazes and sometimes my pieces will crack later on. What's happening? How cool is your kiln when you open it? Your kiln should be within 20 degrees of room temperature before you open it. Keep that in mind always, especially during the winter months. Sudden temperature change will often cause glaze crazing and clay cracking. The "pinging" sound you hear is little crackles forming in your glaze, and this can affect the look and functionality of your piece. And if you have to use pot holders to comfortably handle your pots-close that kiln! Be patient. Good things come to those who wait.
