Crackle, also known as crazing, is a type of ceramic glazing effect that is actually a type of defect. Because of the unique appearance it creates, it is sometimes used deliberately as a beautiful decorative effect. When ceramics are fired, the clay and glaze expand as they get hotter and shrink as they cool. Crazing happens when the clay and the glaze on it expand and contract at different rates, causing little cracks to form as the piece cools. Potters sometimes rub ink in these cracks to make the crackle effect stand out more.
Crawling, like crackle, is another decorative effect that began as a glaze defect. It has many causes, and occurs when the glaze starts to melt. A textured surface is produced, appearing beaded or scaly, and the clay underneath is visible between the scales. To enhance this effect, potters can color the clay itself before applying a glaze designed to crawl, so that the scales may be white over a blue or black background. This type of effect is used to give the effect of lizard or leopard skin, or even dried mud.
Lava glaze is an effect created by adding granite powder to a glaze or by sprinkling salt on top of a glaze while still moist. This causes the glaze to bubble, creating a pitted, cratered surface. Using this type of glazing effect for a food-serving object would not be the best idea because of the pitted surface and the fact that most types of glazes used to create the texture are not food-safe. This effect adds a unique texture to a vase or a sculpture, and it makes a look similar to that of a pumice stone or porous lava rock.