There are various options to improve a firing, either used with or instead of standard kiln shelves. They offer a number of potential benefits:
- the amount of ware that can be fitted into the kiln may be increased
- the ratio of ware:kiln furniture may be increased, increasing firing efficiency
- setters may help maintain the shape of ware in the kiln
- cranks and stilts may allow the underside of the piece to be glazed
Setters are designed to support flat objects such as plates and tiles in a more efficient way than full size kiln shelves. At their simplest, they are discs with 3 lobes that may either contain integral spacer, or may be shaped to sit on standard kiln props. In the kiln they are stacked on top of each other. At the bottom of the stack there should be an air gap between the base of the setter and the kiln shelf, so if necessary the setter supports should be placed on blocks to raise it. Because of their small size, they can be considerably thinner than a full kiln shelf.
The benefits are:
- better packing of the kiln
- improved heat flow round the wares and throughout the kiln
- a reduction in the total amount of kiln furniture
They may also be shaped to help maintain the shape of a piece in a high temperature firing, when the clay is likely to soften soften and deform. In this case, they are geared towards unglazed work, due to the potentially high contact area between the setter and the ware, so are best suited to the commercial pottery approach of making the bisque firing go to maximum temperature, and then use a lower temperature for the subsequent glaze firing. The setter may be anything from a simple disc to keep a rim round, to a support shaped to the underside of the ware to prevent it slumping.
Cranks are similar to setters in allowing pieces to be stacked up vertically, but they are designed to support pieces on sharp points during the glaze firing, so that it can be glazed all over. This is important in making pieces fully watertight that are using clay which is not fully vitrified, but it can be used on any piece where you want to glaze the underside. The limitation of cranks is that the piece is not fully supported, so if it is fired to a high enough temperature that the clay softens the piece may deform.
The pins are generally made of metal or ceramics, and are discarded after the firing as they are likely to have glaze on them. Being thin and sharp, they leave a minimal mark on the glaze, which will generally not be noticed, or they can be polished out if necessary.
If there is any movement in the crank, this may scratch the glaze before the piece is fired. You can avoid the risk of this by filing any gaps with solid wax, which will keep things rigid until the kiln is loaded, and then burn out during the firing.
Stilts are Y shaped metal or ceramic pieces, with sharp pins at the end of each arm. They are used in a similar way to cranks, but in conjunction with a normal kiln shelf or a flat setter. They are available in a wide range of sizes, to match your work - to large a size obviously won't work, and too small a size will make it difficult to balance the ware on top when loading the kiln, as well is increasing the risk of the piece slipping off as the shelves get jogged with more pieces being loaded. Generally the amount of glaze picked up by the stilts is so small that they can be flipped over to use a second time - though if there is any question of glaze getting onto the kiln furniture, discard them.