FAQ: Is Crazed Ceramic Safe?

Is it safe to drink out of a crazed mug?

Just because it feels smooth to your finger doesn’t mean there aren’t thousands of tiny cracks waiting to provide a home for bacteria and make you sick. Don’t drink out of mugs with crazing, unless perhaps you re-glaze with a better fitting clear glaze and fire again.

Is crazing not food safe?

There is a common misconception in pottery, suggesting that crazed glaze surfaces are not food safe because they retain dangerous pathogens. But, through some mystery of the ages, glazed wares exhibiting crazing have been made and eaten off of for over 1000 years.

Is crazing okay?

Crazing on dinnerware pieces is never okay You may have heard it called crackling or even, heaven forbid, grazing. Most collectors use pieces as display-only and therefore accept crazed pieces into their collection though as a general rule, crazing isn’t a good thing.

Can you use pottery with crazing?

Crazing is the effect on pottery which causes it to have a web of tiny cracks over its surface. Although crazing is generally a surface affliction, it can weaken the integrity of your piece in time, as it is opening up the glazed piece of your pottery and thus weakening its overall structure.

Why do mugs crack on the inside?

It’s caused by a slightly poor “fit” between glaze and clay body of the ceramics, usually because of too much silica in the glaze. With some glazes, it’s intentional; celedons craze, as do white raku glazes.

Why do ceramic dishes crack?

In general, cracks result from stresses in the clay. There is always some stress in clay because of the fact that it shrinks as it dries and when it is fired, and it also expands and contracts during firing. Sometimes the stress is too much for the clay to handle and it cracks.

Can you fix crazing?

Crazing can often be eliminated simply by applying a thinner glaze coat. With some glazes, a thinner coat is not an option, but often a slight decrease in glaze thickness will stop crazing. 2. Fire the glaze kiln to the correct cone over a longer period of time.

Why is crazing bad?

Technically crazing is considered a defect in the glaze and can weaken the item. It may also harbor bacteria. So if you are buying pieces to use for serving food you should look for uncrazed pieces. It sits between the lines or in the clay under the glaze so cannot be removed by scrubbing the surface.

How do you stop crazing?

To reduce crazing:

1. Increase silica and clay by 5% silica and 4% clay.
2. Add 5% talc or zinc oxide.
3. Substitute lithium feldspar for sodium feldspar.
4. Substitute borate frit for high-alkaline frit.
5. Apply glaze thinly.
6. Increase firing temperature.

What causes crazing?

Crazing is caused by the glaze being under too much tension. This tension occurs when the glaze contracts more than the clay body during cooling. Because glazes are a very thin coating, most will pull apart or craze under very little tension. Crazing can make a food safe glaze unsafe and ruin the look of the piece.

What does crazing look like?

Crazing can be present in varying degrees. Sometimes items may have a couple of crazing lines on one side and not the other, other times the crazing can look like a spider web and cover the entire item. The cracks are very small and can usually not even be felt, rather just seen visually.

Can you still use dishes that have crazing?

Technically crazing is considered a defect in the glaze and can weaken the item. It may also harbor bacteria. So if you are buying pieces to use for serving food you should look for uncrazed pieces.

How do you fix ceramic crazing?

In practice, the most effective ways to correct crazing are:

1. increase the silica, in body or glaze.
2. decrease the feldspar, in body or glaze.
3. decrease any other material containing sodium or potassium.
4. increase the boron.
5. increase the alumina, i.e. the clay content.
6. increase lead oxide.

Does crazing cause leaks?

Crazing on earthenware pots can cause them to leak, as the fired clay body remains porous and water can seep through. The cracks can also harbour dirt and bacteria, so are not ideal on functional pots.

How do you get rid of crazing on pottery?

Consider some of the suggestions often given:

1. Apply a thinner glaze coat.
2. Add increasing amounts of silica.
3. Remove some feldspar and line blend additions of silica.
4. Firing higher or over a longer time.
5. Add increments of 5% silica to the clay body.
6. Slow cool the glaze kiln, don’t open it until it is below 200°C (390°F)