Glaze material · Colorants
Cobalt carbonate
The strongest blue: transparent if dilute, ultramarine with alkaline fluxes, purple with magnesium, green with titanium.
In published recipes
Used in 1,181 of 10,859 glaze recipes (11%)
Typical amount when present
1% of the dry batch — half of recipes fall between 0.5% and 2%.
Fired surface of those recipes
Glossy 58% · Matte 16% · Semi-glossy 15% · Semi-matte 11%
Most often mixed with
Materials that appear in the same recipes most often.
Chemistry
- Raw formula
- CoCO3
- Molecular weight
- 119
- Fired formula
- CoO
- Equivalent weight
- 119
From Linda Arbuckle's materials table. Mineral formulas are idealized; buy an analysis for the bag you have. Equivalent weight is the weight that supplies one molecule of the fired oxide — the number glaze calculation uses.
What potters should know
Slightly weaker than the oxide but disperses better. Melts at low-fire temperatures. Screen well to avoid spotting; concentrated cobalt spits in firing and leaves blue halos on shelves and neighbours.
Handling and safety
Contains cobalt compounds. Respiratory sensitizer; skin contact can cause dermatitis. Use respirator and gloves during mixing.
Dry ceramic materials generate respirable silica dust. Use a NIOSH-approved N95 or P100 respirator and adequate ventilation when mixing dry, and wet-clean surfaces.
This information is provided for planning purposes and is derived from publicly available sources including OSHA regulations, NIOSH guidance, and manufacturer safety data sheets. It does not constitute professional safety advice. Consult your material suppliers' SDS documents and applicable local regulations for authoritative safety guidance.
Questions
- How much Cobalt carbonate do potters use in a glaze?
- Across 1,181 published glaze recipes containing it, the typical amount is 1% of the dry batch, with half of recipes between 0.5% and 2%. Colorants and additives sit far lower than fluxes and glass formers; treat these as a range to test around, not a target.
- What cone is Cobalt carbonate used at?
- It appears in recipes across the range; the most common cones among published recipes are cone 6, cone 10, cone 9. Where a material sits depends on the rest of the recipe more than on the material itself.
- Is Cobalt carbonate safe to use?
- It carries a specific hazard flag: Contains cobalt compounds. Respiratory sensitizer; skin contact can cause dermatitis. Use respirator and gloves during mixing. Read the supplier's SDS and follow local rules before using it, and never assume a glaze is food-safe without testing.
Related materials
| Glaze material | recipes | typical |
|---|---|---|
| Cobalt oxide | 604 | 1% |
Sources. Usage figures are computed by Claybench over 10,859 glaze recipes compiled from publicly shared community recipe collections (snapshot 2026-02-27) — counts only; no recipe is reproduced, and the figures describe that collection, not every recipe in existence. Material roles and notes are paraphrased from Linda Arbuckle's Ceramic Materials handout unless noted. Hazard notes summarise supplier SDS guidance; read the SDS for the product you buy.
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