Article: Proper Storing of Clay
It's best to store hydrated clay or liquid clay in an opaque, ceramic, stoneware, glass or PET plastic air tight, non-metallic container.
Keep hydrated or liquid clay out of direct sunlight and at cool room temperature. Liquid clay may be refrigerated or left on the cabinet, depending on your preference.
One other thing to consider when storing hydrated clay is that it's important not to 'double dip' when scooping some hydrated clay out of your storage container. Use a clean utensil every time you remove some of the hydrated clay. Do not put your fingers or a dirty spoon (make sure to use a plastic, rubber, or wooden spoon) back into the clay for another dip. It just makes sense to do what you can to keep the hydrated clay as pristine as possible in order to prevent it from being contaminated in any way.
Occasionally scrape the hydrated clay from the sides of the jar into the mass to prevent it from drying around the edges. Hydrated clay has a tendency to get thicker the longer it is kept. If your hydrated clay does dry out, just add water and allow it to reabsorb the water until you have achieved the desired consistency.
Dry powder clay is easily stored in most places, but keep it out of close proximity to gasoline, chemicals, pesticides, herbicides, and anything with a strong odor. Always keep the lid tightly secured on any clay products. If stored properly, powdered clay will keep indefinitely.
Hydrated and liquid clays, stored properly, will last for years. A good indicator that your clay has gone bad is to smell it before using. If it has a sour, perfume, or musty odor, you know it has been compromised. It is not advisable to use in this condition.
Treat your clay with common sense and respect, and it will stay fresh and usable for a long time.