Elementary

Been getting complaints at Club Mud about our Skutt 1227 electric kiln, firing slowly and not wanting to make temperature on cone 6 glaze firings. One of our retired engineer members took a circuit tester to the elements and discovered that the resistance is three or four times what it should be, which means they need to be replaced. Since I did the last repair job on the kiln, I volunteered to tackle the job Monday while I fired my glaze kiln. Sandy Brown, a new member and former art teacher volunteered to assist.

Yeah, those look pretty corroded. Also beginning to droop out of the element channels.

The first step is to pull the hinge pin and remove the lid to a safe location. After that, turn off the breaker and open the switch boxes, so you can disconnect the kiln rings from one another. Always label the wires, so you know how to put it back together.

Because it was hot in the kiln room (also smelly: Karen was burning newspaper out of a sculpture) we took the top ring back into the glazing room to work.

We began by clipping off the power leads and crimp connector on the outside of the kiln, then carefully pulling out element pins with needle-nose pliers. We saved the pins; although the new elements come with pins, there never seem to be enough, particularly of the hook or staple variety.

Old elements are carefully removed, and the channels vacuumed with a HEPA-safe vacuum. (Conventional vacs let silica dust right through, and that stuff is bad for your lungs…)

Afterwards, the new elements are installed, pinning periodically to keep the whole thing from sproinging back out again. Once the element is positioned, we go back and place pins on either side of each corner, with additional hooks or staples for support in places where the brick is worn or broken.

Ceramic sleeves are installed on the outside of the kiln to prevent contact between element and metal jacket, then the ends are trimmed short and the power leads attached with crimped barrel connectors. Repeat until you run out of kiln rings. As it happens, our kiln is hardwired to the wall, so we can't unplug the center ring and take it somewhere cooler, so we balance it on boards on the 818 kiln next door and repair it in situ, taking frequent breaks to hydrate and cool down.

We started the project at 10 am; by 3:30 we're finished, including a lunch break. The manufacturer recommends an initial firing to cone 04 to settle the new elements in their channels, so we close it up and fire it off.

Terminology 2: Electric boogaloo

Time for more terms:

1227. Designates an electric kiln with twelve sides, 27 inches high. Technically it's a model number for a Skutt brand kiln, but potters use it (and the smaller 1027) interchangeably on different brands. My bisque kiln at home is manufactured by Cress, but it's a 1227 regardless of its actual model number.

Kiln rings. For ease of shipping, repair or expansion, most ten and twelve-sided kilns are made of modules, each two bricks high, nine inches, with two elements in each, sharing a control box and switch. You can expand your kiln by removing the lid and stacking on another ring if you need more space, say for large sculptures.

Blank ring. A kiln ring with no elements or switch, usually only one brick high. Used to expand a kiln temporarily to fire something a little too big for the standard size. We've got a 2.25" blank ring at Club Mud for the smaller, 1027 electric kilns.

Element channel. Groove cut into the soft brick to hold a kiln element.

Elements. Long coils of high temperature alloy wire that glow at high voltages--think giant toaster. They're custom wound to fit a particular kiln, with crimps built in at each corner, and a doubled lead at each end that runs through the wall out into the control box. Because they have to provide more heat to compensate for loss through lid or floor, the top and bottom elements are wound with more coils than the center four elements on our kiln.

Element pins. Lengths of high-temperature wire used to hold elements down in their channel. Standard ones are straight, but you can also buy hook-end or staples, which are handy when working around damaged bricks.

Oxide coat. A protective coat of metallic oxide that forms over elements during firing. Repeated firings, particularly with a reducing atmosphere, say carbonates from clay, or smoke from burning out paper in a sculpture, will damage the coat. It will reform again, but leave less element underneath. Eventually the diameter of the element will be enough smaller to affect the resistance and the firing time and efficiency.

Resistance. To electric current. Too little and the elements won't generate heat. Too much and either the current can't get through (again, no heat) or the element overheats and melts.

Crimp or barrel connector. A metal tube that slides over the end of the element wire and the power lead and is crimped (compressed with a pliers-like tool) in place to make an electrical connection.