Firing fine silver metal clay, following manufacturer's recommendations, is very reliable. When firing the other metal clays, you need to follow their guidelines but also become very familiar with your kiln and how it works within the guidelines offered in each package of clay.
If your pieces are not fired, or sintered properly, it would be advisable to increase both temperature and soak time. The higher temperature will sinter the metal properly and the longer soak time will allow the molecules to fuse together for a better overall structure. Each manufacturer offers a maximum firing temperature so you do not reach the metal's melting point--this temperature is established based on the knowledge that some kilns will fire hotter; it is a good idea not to go above this recommended temperature until you know your kiln well. It is also very important that you not go over the highest temperature recommended for any inclusions you may have in your designs.
- Tammy Honaman, Author, Jewelry-Making Expert and Educator