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Home kiln setup buying guide: cones, shelves and a log
Home kiln setup buying guide: Orton cone numbers, cordierite shelves, high-alumina kiln wash, gloves and a firing log that records cone, time and result.
No products were tested for this article, so the items below are named as what the work requires, not as test winners. A home kiln setup buying list is short: cones, shelves and posts, kiln wash, gloves and a scraper, and a firing log.
What to take away
- Pyrometric cones are the one item you cannot substitute. Buy them before the first firing.
- Shelves, posts and kiln wash are consumables, not accessories.
- Leather gloves and a scraper handle the two most common kiln injuries.
- A written log is a tool. Treat it as part of the kit.
Why cones and not the display
A controller reports the temperature its thermocouple sees. A cone reports heat work, which is temperature and time together, at the spot where you placed it.
Cone vs Controller
Controller
- Measures
- Temperature seen
- Factors
- Thermocouple only
- Location
- Fixed probe
- Rate effect
- Readout unchanged
Cone
- Measures
- Heat work
- Factors
- Temperature and time
- Location
- Where placed
- Rate effect
- Bends at different temp
The difference shows in the temperature equivalent chart the Orton Ceramic Foundation publishes for its cones. The same cone number is listed against several columns of heating rate in degrees Fahrenheit per hour, from 27 up to 540 degrees per hour, and it bends at a different temperature in each one.
So a cone number is not a temperature. It is a state the clay and glaze reach, and firing faster or slower changes the temperature at which they reach it. That is why cones stay in the kiln even when the controller is trusted.
Which cone numbers you are buying
Orton cones are the standard sold in the United States, and the numbering runs the opposite way from what most buyers expect: the higher the number, the hotter the firing. Low-fire work sits around cone 06 to cone 04, mid-fire stoneware around cone 5 to cone 6, and high-fire stoneware and porcelain around cone 9 to cone 10.
The bend temperatures follow the same order. Self-supporting cone 04 bends at roughly 1945 degrees Fahrenheit at a slow rate, cone 6 at roughly 2232, and cone 10 at roughly 2345, and each of those moves as the heating rate moves, which is what that chart is for. Buy your working cone plus one number above and one below, so the pack tells you which way the firing went.
The kit
| Item | What it does | Notes |
|---|---|---|
| Witness cones | Show heat work at a shelf position | Buy your target cone plus one either side |
| Kiln shelves | Carry the load | Match the shelf size to the chamber |
| Posts | Set shelf height | Three per shelf, aligned between levels |
| Kiln wash | Protects shelves from glaze runs | Reapply where it chips |
| Leather gloves | Lid and hot metal | Not fabric oven mitts |
| Scraper and mask | Cleaning glaze off shelves | Fired glaze is glass; it cuts |
| Firing log | Makes results repeatable | Paper by the kiln works best |
Shelf material is the choice that lasts longest. Cordierite is the inexpensive standard: light, fine for bisque and low-fire work, but it can warp or crack if you push it to cone 10 with heavy loads. Nitride-bonded silicon carbide shelves, the type sold as Advancer, cost more and are thinner, and they take thermal shock and glaze runs without warping. Posts are sized to stack squarely with them, and house brick is not a substitute.
Kiln wash should be high-alumina, either a commercial high-alumina wash or a mix of kaolin and alumina hydrate thinned to a milky consistency. Avoid washes built on silica, and treat the dried coating you scrape off a shelf as dust.
How the pieces get used
Published studio kiln firing steps put them in order. Kiln wash goes on shelves before a glaze firing, though not for bisque. Shelves are stacked with the smallest work on the bottom and the largest on top, and posts work best in threes aligned from shelf to shelf so the pressure stays consistent.
In a bisque firing greenware can touch and even be stacked; in a glaze firing nothing may touch anything. Witness cones go on the top and bottom shelves. And the kiln stays shut until the temperature reads 200 degrees Fahrenheit.
That last number is the one people ignore. Opening early cracks ware and risks burns, and it is the most common self-inflicted loss in home firing.
What the firing log records
The log is one row per firing, kept by the kiln where you will actually write in it. Give each firing its own line with the date, the clay body and glaze, the target cone, and the cones you placed on the top and bottom shelves.
Then record the start time, the time the kiln reached the target, the total firing time, how long it cooled before you opened it, and what came out: good, cracked, or glazed to the shelf. Over enough firings, the column you will read first is the one that shows your opening temperature creeping up.
The point is not record-keeping for its own sake. A log is what lets you compare a firing that worked with one that did not, cone by cone.
What you do not need yet
A pyrometer separate from the kiln, a second set of shelves, a vacuum designed for kilns, or any glaze chemistry equipment. All of those solve problems you will not have in the first year.
Spend instead on cones, on a downdraft kiln vent, and on the installation done properly, which is where home kilns actually go wrong. The Orton downdraft vent and the Skutt EnviroVent are the two home studios use most, and both pull fumes from the bottom of the kiln and send them outside. Reading the lessons studios write down will save you more than any accessory.
Common questions
Which cone should I buy?
Your target cone, plus one number below and one above, so a cone pack shows whether you undershot or overshot: a cone 5, 6 and 7 pack for mid-fire stoneware, for example. Buy self-supporting cones unless you already own cone holders.
Do I need kiln wash for bisque firings?
Generally no, because nothing melts. It is glaze firings where a run will weld a pot to the shelf.
Can I use house bricks as posts?
No. Kiln posts are refractory and sized to stack squarely. Ordinary brick can spall at temperature and drop debris on your work.
How do I clean glaze off a shelf?
Scrape it with a proper scraper, wearing eye protection and a mask, then re-wash the area. Treat the debris as both sharp and dusty.
