These two pendants were made from Fastfire Bronze Clay... started them as flowers, but I think the reality had another plan for them :)))) - very strange flowers... I was curious how they would fire, as I had open the bronze clay about 2 months before. Which got me thinking, I had not come across the subject of "expiry date" either from metal clay producers or users.
As "organic" fillers are used to produce metal clay, it would be safe to say that there should be some degradation of the filler once exposed to airborne elements (such as oxygen, carbon dioxide, etc.) and bacteria. The level of degradation would be influenced by the type of filler and the airborne particles in a location, along with the atmospheric conditions. It is not my intention to deliver a scientific investigation, but more of a worth noting observation.
This can help to avoid catastrophic loss of many hours invested in the forming of a metal clay piece. So, the golden rule (MY, golden rule ;-), test fire a piece of the clay. I still didn't feel secure about the firing process despite a perfect test firing result. However, the successful result was enough to determine that the clay was not compromised by the delay between opening and using. I fired the pieces in the kiln for about 5 hours at 1625F with no negative impact!
In fact, I've yet to encounter a clay expiring and becoming unusable. But my storage method may have a big impact on this;
lightly moisten the clay with a couple of sprays of distilled water,
Wrap in plastic wrap,
Seal in an airtight container in the fridge.
The "take away".......... test fire & keep a firing log!
You will never appreciate how important this take away until you need it. Troubleshooting a firing failure can be a VERY long frustrating process.....unless you keep records. More on this to come.....