Does Pottery Clay Expire?

Maybe you have a box of Clay that someone gave you five years ago and wonder if the Clay has an expiration date. You’d like to make some pottery, but you don’t want to waste your time if that Clay has expired.

You can hold onto Clay as long as you want without it expiring. In some cases with aging, the Clay gets mold on it, but you can cut away at the moldy parts. Mixing the mold with the Clay will make it more elastic as it ages. Don’t throw it out. 

In this article, we’re going to talk about how to keep your clay fresh even if you don’t use it right away. We will also examine what to do if your Clay gets mold on it or how to deal with other problems.

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What Happens When Clay Ages?

Generally speaking, no, Clay will not expire as it ages. However, Clay does dry out over time. Clay meant for kiln firing won’t go bad.

In cases where the Clay became too Hard and dry to work with, add water to the Clay and wedge it out. Keep adding water until you can wedge the Clay, and it feels moist and workable.

Any potter will tell you that you can manipulate the Clay easier if you keep it moist. Putting a dish of water or Spray Bottle nearby lets you work it into the Clay as needed.

Expert Tip: Don’t add too much water, or the Clay won’t keep its shape. Also, make sure you wedge your clay well. The Clay may form bubbles and have more imperfections that can cause it to crack. The air pockets trapped in the Clay cause it to expand and break in the Kiln.

How to Handle Mold on Clay

As mold grows on your Clay, it can cause discolorations. You have several ways that you can clean the mold from the Clay. First, you can bleach the Clay by spraying the outer surface with bleach water. Use 1/4 of a cup of bleach for each gallon of water. The bleach kills mold on the surface, and as long as it hasn’t reached deeper than that, the bleach will kill the mold.

Remember to use an older towel because bleach will remove the dye in the towel. You will leave the solution to sit on the Clay for the night.

Let’s say that you don’t want to use chemicals. Take the vinegar from the pantry and add it to the Clay. Because of its acidic properties and pH value of 2.5, the vinegar kills the mold. At the same time, you don’t have to dilute vinegar because of its relatively benign properties. Add 20% of vinegar to the water, cover the Clay, and let it sit overnight.

Vinegar will make the Clay feel more like plastic. Plastic-like Clay gives you an advantage because you can work it more easily, and at the same time, it will maintain its form.

The biggest downside of vinegar comes from the smell. Some people can’t tolerate the smell, and they don’t want to work with it in their Clay.

If you don’t have a lot of mold on the Clay, you can cut away at the parts that have mold on them.

If you know you won’t be using your clay for a while you can dry it out to stop it from forming mold and Re-hydrate it a few days before you want to use it. Remember clay needs both oxygen and water to grow, like a mushroom.

Keeping Pottery Clay Moist

Over time, Pottery Clay, which requires a Kiln, will become more workable with moisture. To show you how Clay doesn’t have an expiration date, let’s have a look at history. In ancient China, the Chinese Potters would keep moist Clay in caves to help it age. They’d leave it there until the next generation of potters.

Even today, you still have pottery studios that keep Clay for the next generation. We tell this story to demonstrate that you don’t have to worry about Clay expiring. As long as you keep it moist, it ages like fine wine.

In the modern world, to ensure that the Clay doesn’t dry out, double bag it and place it in a plastic container. If you seal it up tight you have less chance of mold forming on your clay. Mold needs oxygen to grow.

Your natural Clay will last indefinitely. Even if it does dry out, you can rehydrate it. The only way your clay can go bad is if it gets contaminated and starts to break down.

Dry Clay: Can It Go Bad?

Once your clay dries out it wouldn’t go bad, you can rehydrate it when you are ready to use it. Bagged clay can take a few months to dry out if not kept moist. As long as your clay does not get contaminated it will never go bad.

Why Does My Clay Smell Bad?

You open up the bag of Clay to find that it smells bad. Immediately, you think that your Clay expired but did it? When Clay smells bad, take this as a good sign. The Clay has spent enough time in wet conditions with a little oxygen to make it more workable.

To test it, feel the Clay. If it feels like plastic, then you shouldn’t have a problem using it. Smelly Clay indicates that bacteria are living in it, living off the organic matter in the Clay.

Expert Tip: Clay shouldn’t smell extraordinarily bad. If that happens, you may want to add bleach to the Clay and let it sit for a day to kill the bacteria. 

Regular Clay that dries out could be considered as expired, but it has only expired in the sense that you will have to moisturize the Clay again to make it workable.

Don’t Let Clay Freeze

Let’s say that you accidentally left your Clay out during a frost, and it froze. Freezing the Clay will inconvenience you, but it won’t make the Clay unusable. Think of the ground and how it freezes in the winter and unfreezes in the spring. The same process will unfold with your Clay.

After it has frozen, you will have to let it thaw. This can take a considerable amount of time, which is why you don’t want to let it freeze. To thaw the Clay, add water and continue working it.

Understanding Mold and Clay

Important to note, Clay and mold walk down the aisle hand and hand. The more mold you have in your Clay, the easier it becomes to manipulate. People who have allergies to mold shouldn’t work with Clay at all, because all Clay will have some mold in it to one extent or another. Mold helps the aging process of the Clay, which explains why some Chinese potters prefer to let it age for the next generation.

If you can handle the smell and you are not allergic, using clay with mold in it is totally worth it. Speaking from personal experience, it is awesome! It is so workable and great to throw with. But I can’t stand the smell so use vinegar instead.

For more detailed information on storing clay check out How to Store Pottery Clay

Conclusion

Hopefully, you understand pottery clay better because of this article. If you have had clay for 10 years or more, you don’t have to buy new Clay, even if it’s dried out or moist (which can make it better). So hold onto your clay there’s no need to throw it away. Let’s stay dirty!