Crackle is the name given to the method of intentionally forming fine cracks in the glaze-base as a decoration, and crazing is the name for accidental crackle. One can buy a glaze-base with this texture prepared. When mixing the crackle-base with water, it must not be passed through the sieve as it has a very fine, sand like texture, which causes the cracks. Crackle appears after firing, during the cooling down process and is caused by the glaze contracting more than the bisque.
Before opening the kiln, while it is cooling down, you can hear it clicking as it shrinks and breaks. When taken out of the kiln, the texture is difficult to see, so to accentuate it, rub the whole piece using a cloth dipped into a prepared color; strong brown is the one usually used. As the paint integrates into the cracks, the lines appear. Then rub it with a soft, disposable paper, taking off all the unnecessary color. If the piece is going to be used for decoration, it can be left as it is, otherwise it should be fired again. Remember that non-fired colors could be poisonous. One crackle glaze can be laid over another and very interesting results can be obtained. Crackle weakens the glaze and is not advisable to use for outside work where the temperature varies or for something that is going to be continually used.
Crackle surfaces when used a lot get damaged. The next four photos are of two different crackle plates decorated by us. I have used them in my house for about six years and only for keeping fresh fruit. These are to show how the dirt from the fruit and frequently washing the bowls has affected the crackle; it has integrated and cannot be cleaned off. The plate above is still perfect, it is older but has never been used as it has been hung up as a decoration.