Frozen clay suffers laminations. Does that really harm it?

No. Ordinary laminations from improper pugging can simply be wedged out and the clay is still fine to use. But freezing is a different matter. No chemical changes happen when clay is frozen, the water connections between clay particles are simply disrupted. Frost has taken this piece of clay well beyond simple laminations, but it has not become soggy - it can be brought back to normal workability by more thorough wedging. What if the clay gets frozen solid and is soggy and falling apart on the edges? Will wedging restore the workability? Yes. But it will require a plaster slab or table and rubber rib (to be able to deal with the mushy material) and determined wedging - but it is certainly doable.

Related Pictures

Laminations in pugged clay: Wedge it or lose the ware

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These are cross-cuts from slugs of a production run of clay that was improperly pugged (inadequate vacuum). The problem becomes evident weeks or months after pugging. In this case the clay body contained 2% talc, our production must make doubly sure to monitor vacuum pressure at all times (or laminations will result). These are not a problem if clay is wedged well before use. If not the laminations "build in" failure points that initiate drying and firing cracks later. Even if pieces survive the drying and firing processes, weaknesses can persist making them more prone to failure-on-impact or stress. This being said, does that mean you do not need to wedge plastic clay bodies if they are not laminated? No. All clays laminate to some extent when pugged.

Here is how plastic pottery clay should behave (assuming it has not been frozen)

It is winter. It is easy to underestimate the danger of clay getting frozen. Or partially frozen. Storage close to a cold wall or transporting it in the back of a truck are common causes. If your clay is splitting, falling apart, mushy or unthrowable it is almost certain that it has been frozen. Only highly plastic clay will extrude from our pugmill, any sudden changes in plasticity are thus immediately noted by our staff (as it tears coming out of the nose of the machine). You should be able to bend and stretch (as can be seen in this video) any of our products.

Can frozen clay be used? Have we been wrong all along?

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The slug of M340 clay on the left was frozen solid. After thawing, although it was cold and mushy, I warmed up a piece in the microwave and wedged it thoroughly on a plaster table. Although a little soft it throws normally. Are tales about frozen clay being useless really true? I repeated this the next day and made a much larger bellied vase, it worked even better. After all, the clay was frozen and thawn millions of times in the ground before we dug it out.

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Glossary

Wedging
The process of mixing a plastic clay by hand before forming it. Similar to kneading of bread dough, it is considered an essential step by most potters.

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