Kiln: All types of metal clay can be fired in a kiln. As long as the kiln can ramp up to the required temperature (as high as 1650 degrees F (900 degrees C) and can hold that temperature for anywhere from 10 minutes to 4 hours, it can be used for firing metal clay. Check the clay manufacturer's time/temperature requirements to determine how high and how long it must be fired. The main issue with using a kiln, however, is that you want to make sure the temperature gauge is accurate and the length of time the temperature is held is also accurate. If metal clay pieces are under-fired (for example fired at lower temperatures than necessary or for a shorter period of time than required), then the piece will not be fully fired and will be subject to breakage because the organic material will not be full burnt out of the clay. Programmable kilns, such as model #703-117 and -118 from Rio Grande allow you to set the time and temperature for firing, and this means removing any guess work.
Cone System: This system is made up of a fiber cone, mesh grid, and pyrometer connected to a butane fuel tank. One model manufactured by Metal Clay Supply is called the SpeedFire Cone System. Because butane burns well above the 1650 degrees F (900 degrees C) mark you need for metal clay, it gets hot enough for firing. It is also less expensive than a kiln and a little more portable. However, there is no way to program this unit, and it is important to keep an eye on it during the process since the firing area of the grid is not enclosed inside anything.
Butane Torch: You can pick up a hand-held butane torch at just about any hardware store or jewelry supply company. A torch is about the least expensive piece of equipment you'll find that will fire metal clay; however, you are limited to the low-fire varieties of clay and the size of the pieces you plan to fire also have a limit of no more than 25 grams of clay. While the firing only takes about 5 or so minutes depending on the size of the piece, obviously since you have to hold the torch as you fire, it will require your complete attention.
Hot Pot: Similar to the torch, you are limited to small amounts of low-fire metal clay when using a hot pot, but you have the added advantage of not having to watch it for the entire firing process. I love my little hot pot and have used it for firing all types of small charms and pendants. It is a good way for beginners who may not be comfortable using a torch to get started with metal clay without having to spend that much money.
Gas Stove: A regular gas burner can also be used for low-fire varieties of metal clay that are 25 grams or less in size. It's best to cover the burner with a metal mesh to make sure your piece doesn't fall into it, and of course, for safety reasons you can't just stick something on your fired up burner and walk away. As with all types of firing equipment, proper ventilation is essential when firing.