Workable clay has tiny pockets of water, which makes it soft and malleable. However, even a minuscule amount of water trapped in clay will separate from the clay particles and expand, turning it into hard solid clay at very low temperatures.
Here’s what you should Know about Pottery Clay in Extremely Low Temperatures
Pottery clay freezes at extremely low temperatures. As water particles expand, they push clay particles apart, causing cracks on the clay. Stiff clay is not effective for making pottery. If frozen clay is put in a warmer environment, it will become soft again because its particles will contract.
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At What Temperature should you Store your Pottery Clay?
Keep your clay at a little lower than room temperature of 45° to 59°F, preferably in a cool atmosphere. Such a temperature range is not too dry to harden the clay and not too cold to make it freeze over.
Always prevent sunlight from directly hitting the clay and, if possible, keep the clay in a place with some darkness.
The ideal storage location would be an old, dead freezer or fridge that’s kept in the shade. However, if it’s summer and you don’t have an old fridge, wrap the clay bags with draping wet towels.
The whole point is to keep your pottery clay soft and workable in a humid environment and prevent it from hardening on its own by losing the moisture in it.
Will Pottery Clay Freeze in Climates with Low Temperatures?
Clay will freeze at a climatic temperature lower than 32°F. Workable clay is moist clay which is simple dewatered slurry.
Water bonds in clay are weak, and when exposed to freezing temperatures, the water particles will quickly separate from clay particles.
Frozen clay is fairly common for potters storing their clay in garages or home studios. It doesn’t happen all year-round, but when your local TV weatherman starts screeching about protecting pipes, pets, and plants for 12 hours of sub-freezing temperatures, you might want to move your clay from the exterior walls of your studio.
Note that letting clay freeze will not hurt it; it could even help it. The freeze-thaw cycle is what happens in nature to make clay in the first place.
How does Freezing your Pottery Clay Affect its Characteristics?
When clay remains in its frozen state, it certainly loses the characteristics that make it suitable for making pottery. An evident characteristic change is stiffness.
The water in the clay body turns to ice which causes a one-third expansion in the water’s volume leading to clay becoming non-uniform (uneven). The resultant clay body will not remain a “throwable” clay body.
Pottery clay loses a lot of water in repeated freeze-thaw cycles. Clay without enough water to soften it and make it “workable” water is generally degraded clay.
Frozen clay will become “extremely short” afterward, meaning practically little to no plasticity left. However, with enough time and patience (and vinegar), the plasticity is recoverable.
Is it Bad for your Pottery Clay if it Freezes?
Consider annual summer, autumn, winter, and spring cycles. If freezing were bad for clay, it seems all our clay ancestors would have been from warm weather regions and countries. Frozen clay isn’t necessarily bad clay because it can be reversed to be soft and workable again.
However, even after its effects are reversed, frozen clay will need some time to equalize moisture content.
If you mix your clay from slip, freezing can be the perfect way of bringing the water content down to a plastic consistency. Freezing also helps the workability of clay by reducing particle size over long periods.
It explains why previously frozen clay often performs okay for potters simply because freezing is like a mini weathering episode.
When unfreezing previously frozen clay, the excess water tends to migrate and seep back into clay in a process motivated by capillary activity. This process can be sped up by micro-fractures developed on the clay at 32°F because of the expansion of water just before freezing.
Therefore, freezing doesn’t do any damage to the clay.
Can you Still use your Clay for Pottery Once it Freezes?
You can still have a great deal of experience with a frozen clay body once it’s thawed. Begin by running the thawed clay through a pug mill, then spread out the clay and cover it with a thin film of water for as long as convenient (the longer, the better).
You’ll end up with a mushy clay-water substance with little to no plasticity at all. The clay body should then be re-pugged at least twice to help complete the integration process.
After successful integration, allow the clay to “rest” for about a week maximum, and it will be ready for use. The freeze-thaw-pugging is time-consuming, but it’s worth it if your clay is as important to you as the finished product.
Will the Quality of your Pottery be Affected if you use Previously Frozen Clay?
Clay often leads to mediocre finished pottery pieces. Potters who don’t thoroughly hand knead or wedge frozen pottery often end up with art pieces made from clay with no homogeneity, with some parts too hard and some too short.
Constant pugging and remixing frozen clay helps get it to a consistency suitable for making uniformly crafted pottery.
Another effect of freezing on clay is the invisible fault lines that develop in the clay. While these fault lines can be wedged away, inadequate wedging may result in spider-like cracks pottery after the final firing.
How can you Restore your Pottery Clay to Normal Consistency?
Frozen clay will seem unusually wet because of water bunching together in between particles of clay. When this happens, you’ll notice varying consistencies in different parts of the clay, making it “unworkable” as it is.
It’s not uncommon to find “just thaw it, wedge, and it’s good as new” in pottery forums. While this is true, it’s not as simple as that, especially when it comes to the wedging department.
For frozen clay doing it once won’t cut it, and you’ll risk making pottery with sub-par clay. Proper wedging to restore consistency requires a lot of patience since you’ll be wedging thoroughly, then wait and wedge again.
Ensure you thoroughly wedge the thawed clay a few times in between breaks, and you’ll finally attain consistency. Be sure to wedge the clay on plaster to help such some water out to regain plasticity.
How can you Prevent your Pottery Clay from Freezing?
If you’re a potter from a fairly cold region, you’ll be dealing with your clay freezing a lot. It could get frustrating to want to make some art pieces to find your clay stone cold.
It’s a big problem. But it doesn’t have to be this way, so here are a few ways you can keep your pottery clay from freezing:
- Warm Atmosphere: Keep pottery clay in a fairly warm place above freezing temperatures. It seems obvious, but it takes a lot of work to do this. If you have a home studio or work from your garage, identify warm insulated places with a controlled atmosphere to keep your clay. It will come in handy, especially during the winter season when you can find your clay frozen just by leaving it in your studio.
- Vitrified Clay: The whole point of vitrification is to reduce water absorption. Nearly vitrified clay absorbs and soaks very little water, which will, in turn, render it resistant to freezing problems.
Finally, whenever you’re hydrating clay for storage, always consider using salty water. Sodium chloride significantly reduces the water freezing point from the usual 0°C to −21 °C.
Such a change will, in turn, significantly reduce the temperature at which pottery clay freezes.
Is it Feasible to Prevent your Pottery Clay from Freezing?
It certainly is.
If you’re making pottery for sale and have timely orders to fulfill frozen clay could inconvenience your artisanal process. Waking up to stone-cold clay can be a pain, and if you have urgent orders to fulfill, you’ll have to get workable clay again, which costs money and time.
Granted, you can restore frozen clay to normal, but it would take a few days to a week to wedge frozen clay to normal consistency. The effort to keep the clay from freezing is minuscule compared to the frustration, disappointment, and time wastage it takes to revive pottery clay to a workable state.