As metal clay is exposed to air, it will stiffen and crack. Moisturize any unused clay and wrap it tightly in plastic. Have two pieces of plastic wrap ready before you start working, one to immediately wrap up straight-out-of-the-package clay you won’t be using, and one for scraps. If you live in a dry environment, run a humidifier in your workroom.
For long-term storage, wrap the clay in plastic, and put it back in the pouch it came in along with a wet paper towel, or in a glass baby-food jar along with a wet sponge. This will keep the clay fresh for a couple of months.
Do not refrigerate or freeze your clay. Re-wet the clay and reseal the container every couple of weeks; you can keep silver clay fresh indefinitely. Due to oxidation, storage times for base metal clays should be limited. Cut off and discard any oxidation that forms on the surface of the clay, then condition the remaining clay.
To store syringe clay, fold a piece of plastic wrap into a square. Place a few drops of water in the center of the square, set the syringe tip in the water and wrap the plastic around it. Place the syringe in its original foil pouch with a wet paper towel. Once a month, re-wet the paper towel and the inside of the plastic cone. Don’t store a syringe in a jar of water for long periods of time — the moisture will wick up into the clay.