Quartz inversion

When clay is fired, first the water evaporates. Then the various organic substances in the clay also begin to oxidise. When the temperature reaches about 573°C, the quartz inversion takes place. The quartz crystals in the clay rearrange, causing the clay to expand about 1% in volume. If this happens too quickly, it can lead to cracks. It is important to increase the temperature gradually and let the quartz inversion happen slowly. If you were to remove your pot from the kiln at this point, it will shrink again by 1% while cooling down.