Firing Metal Clay--Some Advice

 

 

FIRING

Barbara Becker Simon

©2021

 

SAGE ADVICE:  Before you fire your first piece, familiarize yourself with programming your kiln. Run a firing schedule with NOTHING in there--just to work your kinks out. Secondly, DO NOT proceed firing a "real" piece until you roll some worms of clay as TEST firings. When they are done, try to bend them. If they bend nicely, TA DA!!! Now you can jump in! Knowledge is power! Sacrificing some clay, and time with enough testing to feel like you have control, is worth every minute and penny.

 

 

No matter what brand of metal clay you are working with, you must check the enclosed literature and make note of the firing schedule for that particular clay.  Each type of clay has a time and a temperature (or several schedules) that will ensure full sintering of the clay.  Sintering is term that refers to the method of making an object from a powdered metal by heating the object a bit below the melting point of the powder.  Certain temperatures must be reached and held for specific time periods to accomplish the inter-connection between the tiny, powdered particles of metal.  Once you know the firing schedules of the different clays and your piece is bone dry, it is a simple matter to fire correctly.

 

If you are implanting an object or a substance into your metal clay with the goal of firing it in place, make sure that you know what firing schedule that object will tolerate.  For example, putting a CZ gemstone in metal clay at any time and temperature will be successful, but implanting a natural peridot will only work in the lowest firing clay. 

 

There are a number of ways to sinter metal clay.  Torch firing and kilns are the most common choices.  I will, on a rare occasion, torch fire a piece but I normally use a kiln that is conveniently designed for metal clay use.  I have found that most metal clay users eventually will own a kiln as it is the most versatile and dependable way to sinter your piece. 

 

If you already own a kiln that you might like to use for metal clay, just make sure that it heats efficiently and in a timely manner.  Those large kilns used for ceramics are not well suited to metal clay use.  They are not always accurate in temperature and take a really long time to heat up.  Smaller kilns are usually better.  Some people may have an old enameling kiln that would be useful.  Just make sure that the reading on the pyrometer (the gauge that records the internal temperature) is accurate.

 

 

 

Torch Firing:

If you have a relatively small piece that is made with the low temperature firing metal clay, you can sinter with a torch.  Almost any kind of torch can be used.  Many find the small butane torches that are sold in home improvement stores and kitchen stores (crème brulee torches, yum) to be very suitable and convenient for this procedure. 

 

I would not torch fire a piece that has more mass than a silver dollar.  It is also not practical to fire original formula clay that must be fired for 2 hours at 1650˚F.  The lower temperature clays work well for torch firing.

 

Place the piece on a fireproof surface such as a soldering surface, a kiln shelf, or a piece of fiber blanket. Lower the lights in the room to aid you in determining the temperature of the piece by reading the stages of red glow while heating.

 

Bring the piece up to a medium red glow and hold at that temperature for 3-5 minutes while gently rotating the torch on the metal clay. 

 

Once you have accomplished that, you can turn off the torch. 

 

Synthetic stones can be torch fired (but not quenched—air cool, please) but glass is not usually suitable for torch firing.

 

 

 

No metal clay piece is ever fired on the floor of a kiln.   A kiln shelf needs to be placed directly on the bottom of the kiln. You can place four little ceramic “feet” on the floor to support the shelf.  This way, if you insert a tool to remove the hot shelf after firing, you will have room for the tool under the shelf.  These little feet and shelves can be obtained from any ceramic, jewelry or metal clay supplier.  Flat kiln shelves are the best surface for firing flat pieces.

 

An item that is an aid for firing is a little stainless steel cup.  These can be found at kitchen shops in capacities ranging from about a quarter of a cup to two cups.  Stainless steel is a metal that will not easily break down firing after firing.   I can place vermiculite in these containers to support and nestle in non-flat metal clay pieces such as round beads.

 

Vermiculite is a material that I like to use to cushion and support contoured pieces during firing.  It is a material that can be found at garden supply stores and it is used as a soil conditioner.  It is nontoxic and can be used over and over again.  A dust mask is necessary when working with vermiculite.  Vermiculite can be put into the stainless steel dishes or simply mounded onto a kiln shelf.

 

Another way to fire a non-flat piece is to support it with fiber blanket.  This material is used in the glass fusing world and can be adapted to various contours.  It can be used a number of times before it becomes brittle.  It is best to work with a dust mask when using the fiber blanket. 

 

 

Arranging pieces in the kiln:

 

You can fire many pieces in the kiln at the same time, just follow a few guidelines.

 

If you have a lot of pieces to fire they can be arranged very closely because the shrinkage will draw them away from each other.  If pieces touch each other in the kiln, they will generally not fuse together but it is a good idea to keep them apart. 

 

If you have many, many pieces to fire, with the aid of the little ceramic feet, you can stack shelves in your kiln.  I try not to stack so many that the interior of the kiln is completely filled.  This tends to create uneven heating which can result in both under firing and over firing in the same kiln load.   Also, beware that the back corners of a kiln are sometimes a hot spot and try not to shove pieces into those extreme positions.

 

Both flat pieces on the shelf and shaped pieces supported by any of the above methods can be fired together, even on the same shelf.  If I am firing a lot of very dimensional pieces, like beads, I will place them in a large stainless steel bowl of vermiculite and place that on a shelf.

 

With metal clay, you have a lot of leeway in firing.  Simply pay attention to the crucial temperatures (lowest and highest) and to any implants that may be in your piece and you will have success.