The more thought and planning that is put into loading, the better the results. (Photo courtesy of The Edward Orton Jr. Ceramic Foundation.)

Loading a kiln for firing is not a simple matter of placing shelves and stacking ware. The more thought and planning that is put into loading, the better the results. Ware and shelf placement, the size of the load, the firing characteristics of the kiln, and the type of ware being fired are all important factors.

First the Furniture

Kiln shelves come in all shapes and sizes. For economy of space, it is best to choose shelves that are similar in shape and size to your kiln chamber. For instance, use a round or multi-sided shelf in a round or multi-sided kiln.

Keep the size small enough so there is at least 1 in. of space between the shelf edge and the side of the kiln or KilnSitter^TM. Also, allow some room between the top of your ware and the lid of the kiln, and leave space for witness cones to be placed with the ware.

Select posts in heights to accommodate the ware you are firing. Leave some room between the kiln shelves for air to flow, for heat transfer and for the removal of fumes. Half-shelves are very useful to improve air movement in the kiln. Use two side-by-side with a 1/2-in. space between them and you won't lose too much stacking space.

Some kiln manufacturers recommend placing shelves directly on the floor of the kiln. Most suggest using 1-in. posts to keep the bottom shelf up from the cooler floor and create an insulating layer, much like a storm door.

Setters and Stilts

Air movement in the kiln is clearly a big consideration-one of the most important when loading a kiln. Ceramics need to heat uniformly to prevent warping and stresses in the ware. Air needs to move around shelves and around individual pieces.

Plates and tiles benefit from the use of tile and plate setters or stackers. Shelf-style setters allow air to move under the large, flat objects so they heat more evenly. Avoid heating large, flat objects directly on the cooler shelf. If you are firing decorated tiles or plates, vertical setters economize on space, and sets can be stacked to fit even more.

Glazed ware needs to be stilted or dry-footed, or the melting glaze will stick the ware to the kiln shelf (ruining both). Stilts also provide space for air to move around all sides of the ware. Porcelain and stoneware cannot be stilted, as the stilts embed into the ware during firing. Instead, use high-fire kiln wash or silica sand on the shelf and use a prop to prevent sagging.

Consider Heat Distribution

It is important to evaluate heat flow in your kiln and to make this a consideration in loading. Use pyrometric cones to determine the heating characteristics of your kiln so you know where the hot and cooler spots are. Arrange your ware with different-sized pieces on the same shelf to allow better heat flow.

Don't Overfill

Perhaps one of the most important factors in achieving good fired results is having enough air to mature the ware (to burn out the organics in bisque and develop the best colors in glazes). Shelf and ware placement, along with the use of setters and stilts, can help all this, but here are a couple more tips:

• When stacking bisque, invert bowls and mugs opening-to-opening instead of nesting. This helps air move around all sizes of a piece and prevents black rings and spots in the bottom of the ware.
• Fire bisque lids and bottoms together. To get the best fit for lids, fire them on the piece they match. This will let the two pieces shrink together so you get a good, tight fit. Fire all glaze pieces separately.
• Leave space between ware. There is a temptation to cram as much as possible in the kiln to economize on firing costs, but ware fired too closely together creates firing problems. If you must overfill, fire very slowly and vent adequately.
• Mix thin- and thick-walled pieces together throughout the load. Don't concentrate them in one area where they are competing for air and heat.
• Use downdraft venting to move air through the kiln and to remove fumes created during firing.

Editor's note: This information has been provided by The Edward Orton Jr. Ceramic Foundation. For additional information, visit www.ortonceramic.com.