Base Metal Clays

The term "Base" metal clay refers to any of a number of non precious metals and alloys such as copper, brass, bronze, steel, and all the colorful variations of these metals. For firing purposes you can include the alloy of sterling silver.

All of these clays sinter the best when fired in a kiln in a two part process that includes an open firing to burn off the binder and a second firing in granulated carbon which prevents oxygen oxidation. Some base clays can be fired with a torch in very small charm-like sizes, but this method does produce much more oxidation which may affect the depth of the texture.

Oxidation prevents full sintering because two particles of metal which have an oxidized 'skin' cannot fuse or 'sinter' to each other.

Each brand and formula of base clay requires a specific firing schedule which may, or may not, work for another brand or formula. The best option is to do a test firing using the manufacturers suggested schedule, and 'tweek' it to fit your kiln's actual firing quirks. Some kilns may fire a bit hotter than the digital read out, some may fire a bit cooler than the digital read out. Firings can be affected by how many pieces you have in the container at once, the amount of carbon on top and below the pieces, the specific type of carbon, and the container itself (ceramic, fiber, or steel, for example - ceramic containers tend to hold heat better than the others which means they may fire hotter than the readout). Some base clays can be co-fired and some cannot. You should do some research before you begin a more complicated project.

Tips and Tricks
• How to refresh carbon from Bill Struve:
"It can be reactivated by soaking in water, pouring the dirty water off, air drying, and firing by itself for half an hour at 1000F."
• About Firing Pans
There  are any number of containers you can use when carbon firing. These include round, stainless steel pet bowls, stainless steel restaurant type 'steam pans', fiber boxes, and ceramic containers. Martha Biggar sells a pan made out of a higher grade stainless steel that doesn't spall.