Ryan Greene

Ah, well I hope you don’t have to abandon the glaze! As for the sand wads, simply place the piece where you want it loaded in the kiln and trace a light pencil mark to show the footprint. I’ve been taught to use a very small scoop to place quarter to half dollar sized piles of sand that can be up to about 1/2” tall as needed. Place as many piles as needed to prevent slumping, and you can sweep it off the shelves and reuse it forever. You may need to sieve out small kiln wash chunks over time. Good luck!

Hi Kristina, As many people have said, this is definitely a crack that occurred in the cooling process. I see this as being the cause of either direct contact with the shelf over a wide area, or more possibly, a glaze fit problem. It seems this form has no foot/flat bottom, so using small sand pile “wads” on the shelves could allow the floor to cool evenly with the walls. Hollow core shelves or advancer shelves cool more evenly, but sometimes, they do not cool fast enough to keep up with the wares of much less mass. Using a thin layer of sand may help prevent it from sticking to the shelf, but may not create enough space between to allow for cooling to occur evenly. I think using waster slabs would only perpetuate the problem because it doesn’t go so far to separate the two masses. If you do try to slow cool, I would look at focusing on temperatures closer to quarts. At 1600, the pieces are still very vulnerable to cooling cracks. If you need to slow cool through quartz to prevent cracks like this, then I would say there’s a bigger problem at hand anyways. This brings me back to my original thought which is glaze fit! Do you mix your own glaze? Do you know if this has lithium? Lithium has one of the lowest thermal expansion rates among ceramic materials and almost always causes dunting cracks when only used as a liner glaze. Have you had this problem with other glazes? It could also be the clay body contributing to a poor glaze fit, so there could be a little testing in that.