If stored properly, polymer clay can last for years. Improper storage, however, can ruin the clay or damage other objects in your home.
The two major threats to the longevity of polymer clay are direct sunlight and excessive heat. Either thing can partially cure clay, which will ruin it for future use.
When you purchase clay, be sure to bring it inside immediately when you get home. If you're going to be making additional stops before going home, you'll want to take measures to protect the clay. The inside of a car can become incredibly hot in a short period of time during the warm months of the year, so you should never leave your clay in the car unprotected. Put it in a bag and carry it with you, if you can, but if you must leave it in the car, it would be best if you could store it in a cooler with an ice pack.
Once you've gotten your clay home, you can store it in a number of ways. Before it is opened, you can leave it "as is"; the plastic wrapper will keep it free of lint and dust. However, once you've opened your clay, you'll probably want to re-wrap the left-overs. Some people use wax paper to wrap individual blocks of clay. Others use clinging plastic wrap (such as Saran Wrap). You can also use plastic sandwich bags; the types with zip closures are especially convenient.
It is generally advisable to avoid extended contact between raw (uncured) polymer clay and hard plastic containers. Some plastics will react with the plasticizer in the clay (the thing that makes the clay soft and pliable). This can create a gooey mess that ruins both your clay and your container. Some people report that polymer clay can have a similar reaction to plastic wrap. Plastics that have a recycling number of 2, 4, or 5 are usually fine for storage. (Look at the bottom of the container for the recycling logo-a triangle formed by arrows. The recycling number will be in the middle of that triangle.) If you're in doubt, you can always run a test, as long as you aren't worried about ruining the container. Just put a bit of clay in the container (or wrap it in the plastic), and in a day or so, you should know if it's going to work. (Don't use it if the clay has stuck to or eaten away at the plastic-that's your indication that it's not a compatible blend of plastic.)
Polymer clay can be stored at room temperature for extended periods of time, but it will last even longer if kept in a cooler place, such as in your refrigerator. Some people even freeze their clay. (Just be sure, if you put it in either place, that the clay doesn't come into contact with food!)
A few extra tidbits:
- Never store cured clay with uncured clay. The plasticizers will leach back into the cured clay and cause it to weaken and possibly break.
- Don't put uncured clay on any unprotected surface-furniture, tables, countertops, rugs, or floors-because the clay can ruin them. Always work on a clay-dedicated surface. (A ceramic tile is the general favorite.) Once clay is cured, you may put it wherever you like, so long as it doesn't come into contact with food.
- As long as clay is completely wrapped, it is safe to store in any type of container.
- Unwrapped clay won't dry out, but wrapping keeps airborn particles from sticking to the clay, which seems to act as a dust magnet. If you like, you can leave uncured clay on your work surface with just a sheet of plastic wrap draped over it to keep it clean.
- Wrapping clay makes it easier to store in a compact place without the different colors of clays touching. (This can lead to color transfer between blocks of clay.)
- Some people find that certain tackle boxes, in particular, don't react to clay, which makes it possible to store unwrapped clay or canes very easily.
- Glass or metal containers are fine for storing raw polymer clay.
- The rule of thumb with polymer clay is that once anything (knife, cheese grater, pasta machine, cutting board, food processor, container, etc.) has come into contact with the clay, it should be "clay-dedicated". This means that you shouldn't use it again with food.