Crazing

What is it? Crazing appears as a web of fine cracks in the glaze. It happens when the shrinkage rate of the glaze is greater than the shrinkage rate of the clay body - the glaze becomes too small for the pot and this causes it to crack. Sometimes this is exactly the look you were going for - crackle glazes are actually designed to do this, but be aware that cracked glazes are not considered food safe as they can harbour bacteria.

How can I avoid it? Since the problem is a fit issue you need to try either a different clay or different glaze - for example our mid-fire turquoise has a tendency to do this on some clays but works well on porcelain.

shivering

What is it? Shivering (sometimes called ‘chittering’ when over the rims of pots) is basically the opposite of crazing - it happens when the shrinkage of the clay body is greater than that of the glaze and the glaze peels or chips off.

How can I avoid it? As with crazing, the problem is a fit issue so you need to try either a different clay or different glaze.

Crawling

What is it? Crawling is when the glaze has separated and pooled and left bare patches. It is often caused by dust on the pot or glaze being applied too thick. it tends to happen more with matte glazes

How can I avoid it? You can fit it by making sure you blow your pots with the compressor or use a slightly damp sponge to remove dust.

If you are layering glazes, try spraying them for thinner coats and avoid layering one matte glaze over another.

Running

What is it? Running is when the glaze melts and drips down the pot. Some glazes, like Chun, are designed to do this and will have extra flux in them to create this effect, but it is never desirable to have the glaze run down your pot and onto the kiln shelf. It is often cause by layering glazes or applying them too thickly.

It can also be the result of putting a lower-firing glaze into the high-fire kiln.

How can I avoid it? Apply a thinner coat. If you are going to layer glazes never double dip the outside of the pot lower than halfway and always leave half a centimetre of bare clay the base of the pot. If you suspect your glaze might run, put it onto a separate broken piece of kiln shelf .

Always make sure you put the right glaze into the right firing temperature.

Blisters and pinholes

What is it? These are caused by air pockets in the clay body that get caught in the glaze when it is fired. Pinholes penetrate right to the clay body.

How can I avoid it? Make sure your clay is well wedged before you use it. Ensure it is well-sanded and free from dust when you apply your glaze and don’t apply it too thickly.