Technical methodology
🇧🇷 PortuguêsThis page describes the criteria Keramoslab uses to classify each AI-generated glaze recipe on a scale of 1 to 4. The system combines 3 axes in a decision tree, anchored in the applicable regulatory standards (RDC 42/2013 — MERCOSUR, ISO 6486-2, FDA CPG 7117.07, ASTM C738) and the IARC (WHO) carcinogen classification.
It is a technical screening — guidance, not a verdict.
The score evaluates a formula (the recipe), not the finished product. It exists to give the potter confidence and a documented starting point — the final word on food use is the migration test (ASTM C738) on the actual piece. That test is not legally required: Brazilian norms (like most countries') only set migration limits for lead and cadmium. The other colourant oxides (copper, cobalt, iron, lithium, etc.) have no regulatory limit — several are micronutrients and, in practice, migrate below the body's daily requirement. That is why the “moderate” band does not mean “toxic”: it means “confirm with a test if it will contact food.”
All oxides in the SAFE band, OR up to 3 oxides in the MODERATE band — which, locked into a stable vitreous matrix (Axis 2), are immobilized and protected from leaching. No prohibited oxide (Pb/Cd/Be) and none in the RISK band. Axis 2 (Seger) stable (R₂O/RO ≤ 0.45 with adequate Al₂O₃). A theoretical screening as safe for food contact — confirm with a migration test (ASTM C738) on the real piece. Firing maturity (Axis 3) is a bench-test caveat, not a blocker.
Four or more oxides in the MODERATE band (accumulated load) OR Axis 2 (Seger) borderline/unstable. May be used on the outer part of a utilitarian piece (foot, exterior); for food contact, run the migration test.
An oxide in the RISK (high) band on Axis 1, OR R₂O/RO > 0.45, OR insufficient SiO₂+B₂O₃ for the temperature, OR Stull indicates a matte/unstable matrix. Do not use on pieces that touch food.
PbO > 0 OR CdO > 0 OR BeO > 0 (any amount — the only metals with a migration limit in the norms) OR Cr₂O₃ in the risk band under an oxidizing atmosphere (Cr⁶⁺ likely). Reformulate before testing.
Percentages over the base glaze. References: international ceramics literature + ASTM C738 (leach test) + ANVISA guidelines.
| Oxide | Safe | Moderate | High | Technical note |
|---|---|---|---|---|
Cobalt CoO | ≤1.2% | >1.2%–2% | >2% | Optimal up to ~1.2%; 2% is the ceiling traditionally accepted by potters. Above 2%, excess cobalt tends to leach in acidic media. (Species commonly used in ceramics: CoO.) |
Copper CuO | ≤2% | >2%–4% | >4% | Copper is aggressive to the glaze; above 4% leaching becomes perceptible. Copper is an essential micronutrient and is not capped by food-contact migration norms. |
Chromium Cr2O3 | ≤1% | >1%–2% | >2% | Above 2% it may form soluble chromates (Cr⁶⁺) in acids. IN REDUCTION the limits are more permissive (safe ≤2%, moderate >2%–4%, high >4%) because Cr⁶⁺ does not form. |
Manganese MnO2 | ≤4% | >4%–7% | >7% | Hazardous by inhalation as raw powder; for food contact prefer ≤4%. |
Iron Fe2O3 | ≤8% | >8%–15% | >15% | Iron is relatively stable, but excess destabilizes the glaze. |
Nickel NiO | <1% | 1%–2% | >2% | Allergen / IARC-listed. Use a stable, well-vitrified matrix; above 2% is flagged for decorative use. |
Vanadium V2O5 | ≤3% | >3%–7% | >7% | Toxic at high concentrations; stability depends on the glassy matrix. |
Titanium / Rutile TiO2 | ≤6% | >6%–10% | >10% | Rutile is stable, but excess can create a rough surface that traps soil. |
Barium BaO | ≤3% | >3%–5% | >5% | Locked into a stable matrix it is inert; in a weak matrix it leaches. For functional ware, strontium (SrO) is a safer substitute. |
Strontium SrO | ≤3% | >3%–5% | >5% | A safer alternative to barium for matte/satin fluxing. |
Zinc ZnO | ≤8% | >8%–15% | >15% | Low toxicity — the real risk of excess is a physical defect, caught by the Stull analysis. |
Zirconium ZrO2 | ≤10% | >10%–15% | >15% | Economical, stable opacifier. |
Lithium Li2O | ≤3% | >3%–6% | >6% | Powerful alkaline flux; high amounts lower the matrix's chemical resistance. |
Lead (PbO), Cadmium (CdO) in any detectable amount — these are the only metals with a food-contact migration limit in the norms (RDC 42/2013, ANVISA Ordinance 27/1996, FDA). Beryllium (BeO) is never acceptable (IARC Group 1). Any presence sends the score straight to 4.
A stable matrix is the real safeguard against leaching: the harder and more vitrified the glass, the less any metal migrates. The system reads three signals — R₂O/RO ratio(excellent ≤0.20, ideal 0.20–0.35, attention 0.35–0.45, high >0.45), glass formers SiO₂+B₂O₃ (adequate range depends on the firing temperature), and alumina Al₂O₃ (ideal 0.25–0.45 mol for high temperature). A commercial frit with no declared composition is treated as stable (it is industrially insoluble by design), not as a failure.
The finish is inferred from the SiO₂:Al₂O₃ ratio on the Stull Chart (a glossy, vitreous surface in the ~5–12 zone is best for food). Firing maturity is a bench-test caveat and does not lower the score on its own — cone inference carries ±30–50 °C of uncertainty, so a digital pyrometer reading without a pyrometric cone is never treated as a verdict.
Questions or technical feedback? Write to suporte@keramoslab.com.br.
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