Loading a kiln looks like the easiest job in the studio. Then a shelf cracks under a stack of bowls, a glaze runs onto a shelf, or the cones bend two numbers hotter than planned and a whole firing needs unpicking. Almost all of that is decided before the lid goes down.

What follows is the checklist worth running through every time, whether you're candling a bisque load in a small top-loader or packing a glaze kiln the night before a fair.

Start with the shelves, not the pots

Before a single pot goes in, inspect the shelves. Sight along each edge; a warped shelf rocks on a flat bench and will only get worse with heat. Check for hairline cracks, chipped corners and patches where the kiln wash has flaked. A shelf that has spalled once will usually keep doing it, and a shelf that fails mid-firing takes the layer above it with it.

Re-coating kiln wash

Kiln wash is the only thing standing between a runny glaze and a shelf you can never clean again. Scrape back the old coat and apply two or three thin layers rather than one thick one, letting each dry. Thin is the point: thick kiln wash flakes and lands on your work.

Many potters coat the top of each shelf and dust the underside with kiln wash or alumina hydrate so it doesn't stick to the shelf below. Let shelves dry completely, overnight if possible — a damp shelf in a closed kiln becomes steam, and steam lifts glaze. While they dry, sort your posts. Anything chipped at the end, or with old glaze on it, goes in the bin. Keep matched sets at fixed heights so you always have four the same.

Shelf placement and stacking

How you place the shelves decides how evenly the kiln heats. A few rules cover most situations.

  • Stand the first shelf on posts, never flat on the kiln floor. Air needs to move underneath.
  • Leave at least 10mm between the shelf edge and the elements, more if you can spare it. Shelves pressed against elements scorch and shorten element life.
  • Keep ware 20–25mm clear of the kiln walls so hot air can circulate.
  • Off-set your posts between layers. If every post sits directly above the one below, you build a solid column and heat struggles to move sideways.
  • Aim for a comfortably full kiln. An empty kiln fires fast and unevenly; a crammed one fires slowly and unevenly in different ways.

Bisque versus glaze loads

Bisque firings are forgiving. Greenware can be nested, bowls can sit inside other bowls, and pieces may touch, because nothing is molten yet. Leave room for air and steam to escape, and don't stack so heavily that the bottom pieces carry real weight.

Glaze firings are the opposite. Nothing may touch anything else. Leave a generous finger's width between pots, and never place a piece directly above glazed work — one run or a blown bubble will weld two pots together. Put anything with a runny glaze on a kiln-washed tile, a shell or a bed of alumina. A cheap waster is far less annoying than a ruined shelf.

Witness cones and kiln sitters

Witness cones tell you what the kiln actually did, which is not always what the controller said. Use a three-cone pack: one number cooler than your target (the guide), your target cone, and one number hotter (the guard). When the guide is down flat and the guard is just beginning to bend, the firing landed where you wanted it.

Place cones where you can see them through the peephole and where they read the real temperature — mid-height, away from walls and elements. In a tall kiln, use packs at the top, middle and bottom. When the top cone is down and the bottom one has barely moved, that tells you to think about shelf placement and element condition, not just soak time.

If your kiln uses a sitter, treat the junior cone in the mechanism as the shut-off and the witness cones as the record. On electronic kilns, still use cones, especially for glaze firings. Thermocouples drift and controllers get knocked out of calibration; a bent cone doesn't lie.

Ventilation and the space around the kiln

Every firing produces fumes. Bisque firings burn off organic material and sulfur; glaze firings release metal oxides and, from some materials, fluorides. You want those leaving the room, not settling in your lungs or on your pots.

On a small electric kiln, a powered downdraught vent is the quietest solution: it draws fumes from the base of the chamber and pipes them outside. An overhead canopy hood works if it's sized for the kiln and the room has a supply of replacement air. Otherwise, a window and an open door on opposite sides give you a cross-draught. Whatever you use, run it from the moment you switch on. The first hour is when most moisture and organic burn-off comes off, not the last.

Gas kilns need proper flue extraction. Any kiln in a garage or a room attached to living space deserves serious thought, and a carbon monoxide alarm is cheap insurance. If you're unsure about an installation, ask a qualified person and check what your local authority requires. Clear the area while you're at it: no paper, solvents or bin bags against the kiln, and nothing resting on the lid.

Kiln furniture: what to load and what to leave out

Keep a dedicated set of furniture and inspect it each time. In goes: matching posts

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