So what is "Metal Clay"?
Metal clay first emerged on the craft scene out of Japan in the 90's. It was created to allow jewellery artists a medium to create without the large investment required for casting and fabricating using traditional metalsmithing techniques.
Metal clay is a clay substance made from microscopic metal particles mixed together with water and a non toxic, non allergenic, organic binder. Metal clay feels very much like porcelain clay used by ceramic artists.
Like ceramics, metal clay can be manipulated and shaped, left to dry and then fired to create a solid, usable object.
However, unlike pottery clay, the organic binder is there to hold the metal particles together while you work. Once you are finished (and your piece is dry) and ready to fire, you can use a kiln and in some cases a butane torch to fuse or 'sinter' the metal. During the firing process, the organic binder burns away allowing the metal particles to melt and stick to one another, leaving you with a solid metal piece.
Metal clays are available in noble metals (fine silver, silver alloy: sterling silver, and gold) as well as base metals (copper, bronze, iron, steel and brass). The majority of metal clays contain reclaimed and recycled metals.
The secret to metal clay is a process called “sintering.” When metal clay is fired, the water and organic binders in the clay burn away. The remaining metal particles are heated to a temperature below the melting point to allow the particles to fuse together creating one solid piece. Each type of metal has it's own unique temperature and firing requirements.
Some fine silver clays may be torch fired while most require a kiln.
Some clays require a two stage firing where the piece is first put on an open shelf to burn the binder off and then later embeded in carbon for a second firing. Other clays can do a single stage (some with, some without the carbon).
Each clay has a different melting point and different temperature ranges required to properly sinter.
As well, different clays have different shrinkage rates (due to the burning off of the binder and decreasing the volume). Shrinkage rates range from 8%-30% depending on the manufacturer.