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Home kiln setup materials: clay, cones, glaze and testing
Home kiln setup materials in order: a mid-fire clay body, matching Orton cones, dinnerware-safe glaze, shelves and kiln wash, then tile and leach tests.
Choosing home kiln setup materials is one decision made three times: the clay body sets the cone, the cone limits the glazes, and the glazes decide whether the ware can hold food. Getting them out of order is how people end up with a shelf of pots they cannot use.
What to take away
- Choose the clay body first. It fixes the cone, and the cone fixes everything downstream.
- Match glaze to body and cone, then test on a tile before committing a load.
- Food safe is a property of a fired result, not a claim on a jar.
- There is no known safe level of lead exposure, which is why the testing question is not optional.
The order of decisions
Body, then cone, then glaze, then use. One mid-fire stoneware fired at cone 5 or 6 covers most home work, and staying on it matters because shrinkage, glaze fit and firing behavior all belong to that pairing. Low-fire earthenware sits around cone 04, high-fire stoneware and porcelain around cone 10; swap the body and every glaze result becomes a guess again.
Order of kiln decisions
Choose clay body first
pick cone from body's maturing range
glaze results become a guess
| Decision | Fixed by | Do not change it because |
|---|---|---|
| Clay body | What you make and how you fire | Every glaze result was measured on it |
| Cone | The body's maturing range | Shelves and other work assume it |
| Glaze | Body plus cone plus thickness | Fit failures are structural, not cosmetic |
| Food use | A tested result on that pairing | The label describes the glaze, not your pot |
Which materials to buy
Every item on the list is chosen to match the one before it:
- Clay body.One mid-fire stoneware, such as Laguna B-Mix 5, bought from a supplier that publishes a data sheet for it. The data sheet names the cone the body matures at.
- Cones.Pyrometric cones from Orton in the number on the data sheet, cone 6 for a cone 6 body, plus one cone cooler and one hotter (5 and 7) so you can read where the firing actually landed.
- Glaze.A prepared commercial glaze from Amaco, Mayco or Spectrum, picked from the ones the maker labels dinnerware safe and rates for your cone.
- Kiln furniture and shelf protection.Cordierite shelves, kiln posts in a few heights, kiln wash for the shelf tops, and shelf paper where a glaze might run.
- Kiln and ventilation.A kiln sized to your shelf and wired to a dedicated circuit, with a vent or hood that carries fumes outdoors.
What a food-safe test actually involves
The phrase gets used loosely. The laboratory method behind it is ASTM C738, which holds the fired surface in acetic acid and measures the lead and cadmium that come out, and a college chemistry project tested community studio glazes for leaching with a protocol in that family.
How a leach test runs
- Coat vessels with each glaze
- Fill with 4 percent acetic acid
- Leave 24 hours at room temperature
- Analyze with atomic absorption spectrometer
- Resulttrace metals below threshold unseen
Two things there matter at home. The studio already avoided lead and cadmium, using copper, cobalt and iron as colorants, and the work still needed testing to say anything. And the supervising chemist noted a limit on every such test: they could not say no metals were present, because the instrument misses trace amounts below a threshold.
That is what a real answer looks like. It is not a sentence on a label.
Why the standard is strict
Lead draws particular care because regulators do not treat it as having a threshold. The Food and Drug Administration, in its guidance on lead in food and foodwares, states there is no known safe level of exposure to lead.
The FDA therefore monitors and regulates lead and cadmium levels in food and in ceramic foodware, and it has acted on imported cookware found to leach lead.
The practical rules follow: buy prepared glazes that the maker labels dinnerware safe — the commercial lines sold by Amaco, Mayco and Spectrum carry that labeling on the glazes that qualify — and fire them exactly as directed. Never add colorants to a glaze you will eat from, and keep untested glaze off any interior surface.
If you sell functional ware, pay for a leach test rather than trust a label. Those choices belong in the setup plan, along with the cones and shelves that make firing repeatable.
A test routine you can keep
- Fire one tile of every new glaze on your own body, at your own cone.
- Label the back of each tile with glaze, body, cone and dip time.
- Keep the tiles. A drawer of them is a real reference.
- Retest when you change body, glaze batch or firing schedule.
Common questions
Are lead-free glazes automatically food safe?
No. Lead-free removes one metal. Fit, thickness, firing and other colorants all still affect whether the fired surface leaches or crazes.
Does an acidic food really change the answer?
Yes, which is why leach tests use acetic acid. Vinegar, citrus and tomato pull more from a glaze than water does.
Can I test glazes at home?
Not meaningfully. Home swab kits are a screening tool for lead only, and they do not measure what a laboratory leach test measures.
What about the outside of a mug?
The surfaces that matter most are the ones food and lips touch. Keeping an experimental glaze to the outside wall, below the rim, is a reasonable compromise.
