Some people worry about the line of light that appears around a kiln lid (or door) at high temperatures. They wonder if the light means heat is escaping.

The kiln expands as it heats. The larger the kiln, the greater the overall expansion of parts. Since the hot inner surface of the lid expands more than the cooler outer surface, the lid or door bows slightly toward the firing chamber. This causes a small gap, where light from the firing chamber is visible. The gap is more pronounced on the ends of an oval lid than on a round lid.

But unless the lid rises during firing (the subject of another Kiln Pointer), there is little heat loss from the gap under the lid. At high temperatures, the molecules in air are so far apart that they no longer transfer heat through convection. This is why heat does not pour out of a peephole when you remove the plug.

On some models, we add a gap between the lid (or door) and kiln at the hinge. As the kiln gets hot, the gap closes due to the expansion of the firing chamber.

Before closing the lid of a top-loading kiln, shine a flashlight down into the kiln to check the cone and actuating rod of the Kiln Sitter or the thermocouple of a digital kiln. Position the shelves so they do not block the view of the Kiln Sitter cone or thermocouple from above. (The thermocouple is the rod that measures the temperature of a digital kiln.)

Do not allow a piece of glazed ware to extend past a shelf and over the Kiln Sitter cone or the thermocouple. If the glaze drips from the ware onto the cone and actuating rod, the cone could harden, fail to bend, and overfire the kiln. Dripping glaze could also reduce the life of the thermocouple.

Ware and shelves should be at least 1/2" away from a thermocouple. Position shelves either above or below the Kiln Sitter tube. Never position a shelf directly in line with the tube. This is because jarring the kiln could push the shelf against the Kiln Sitter and prevent the rod from dropping.

For many people, firing a kiln is the high point of the week. But sometimes obligations interfere with creative activities, and the kiln is left in the background for six months or a year.

If this has happened to you, the following guidelines will help you to take up where you left off the last time you fired your kiln.

1) Make sure the kiln is still safely installed. For example, remove flammable materials from the firing room.

2) Look through the kiln instruction manual and reread sections that you highlighted the first time you read it. Reread the safety rules.

3) Reread your kiln notebook. (If you don't have a notebook, it would be a good idea to start a diary where you record discoveries about firing your kiln. A spiral notebook will do, or keep notes in a computer document.)

4) Did your kiln come with a Quick Start card? If so, review the card before firing the kiln. This is especially important for a digital kiln that you don't remember how to program.

5) Make sure the materials you fire are compatible. Glazes must fit clays, and glass that you are fusing must be compatible. If materials are unlabeled, you may have to test them in small batches.

6) Vacuum the kiln if the lid had been left open while the kiln was idle.

A customer asked how to combine Firing #1 and Firing #2 into one firing:

Firing #1

Segment 1: Ramp 650 F per hour to 1000 F. Hold for 2 hours.

After the kiln has cooled down to 200 F, begin Firing #2.

Firing #2

Segment 1: Ramp 650 F per hour to 1000 F.

Segment 2: Ramp 380 F per hour to 1525 F. Hold for 2 hours.

The Combined Firing

Segment 1: Ramp 650 F per hour to 1000 F. Hold for 2 hours.

Segment 2: Ramp at Full to 200 F, no hold.

Segment 3: Ramp 650 F per hour to 1000 F, no hold.

Segment 4: Ramp 380 F per hour to 1525 F. Hold for 2 hours.

In the combined firing, the segment 2 ramp is Full. Since segment 2 is a cooling segment, a Full ramp will turn off the heating elements. They will not turn back on until segment 3 begins.

A heating segment Full rate means heat as fast as possible. The elements will stay on continuously during that segment.

A cooling segment Full rate means cool as fast as possible. The elements will remain off for that segment.