Technical methodology
🇧🇷 PortuguêsThis page describes the criteria Keramoslab uses to classify each AI-generated glaze recipe: the normative classification (three independent indicators) and, for reference, the previous 1-to-4 scale, which combines 3 axes in a decision tree, anchored in the applicable regulatory standards (RDC 722/2022 + IN 160/2022 — ANVISA, 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.”
Since 30 Oct 2026 the main reading of the report is the normative classification (A · M · Q), described next.
The 1-to-4 scale on 3 axes, used from May to October 2026, remains documented below for reference.
main reading of the report
An alternative reading of the same report, as three INDEPENDENT indicators instead of a single grade. It uses no percentage bands per oxide: it relies on the presence of regulated metals, the class of the glassy matrix (computed from the unity formula against the cone's published limits and the Stull map) and each colourant's usual saturation ceiling. It never says "safe" — the best outcome is "passes screening", because compliance is only proven by a migration test.
Vetoed metals (Pb, Cd, Sb on functional ware; Be, As, Hg, Tl, U always) decide A4/A5. Without a veto, the matrix class combined with the colourants present and their saturation ceilings decides. A declared decorative use relaxes Pb/Cd to A4 (with precautions), never to food contact.
A1Food contact · passes screening
May be used for food contact according to the chemical screening. Compliance is only confirmed by a migration test.
A2Food contact · conditional on testing
May be used for food contact after a migration test (ISO 6486 / ASTM C738) or after correcting the matrix/firing.
A3Outer surfaces only
Use away from the food-contact surface (e.g. the outside of a mug).
A4Decorative · with precautions
Decorative piece only. Handle with PPE; dedicated kiln and furniture. Never for food.
A5Restricted · do not use
Material with no safe studio handling, or banned for food contact on the declared piece.
By PRESENCE of the material, not by percentage: the risk of weighing and mixing powder is the potter's and does not depend on the dose in the recipe. Basis: harmonised CLP/GHS classification (ECHA), safety data sheets and IARC.
M1Handling · low
Dust mask (silica) when weighing; wet cleaning.
M2Handling · caution
PFF2/P2 mask and gloves when weighing and mixing; never dry-sand.
M3Handling · high
Carcinogenic, sensitizing or systemically toxic material: PFF2/P2, gloves, ventilation; dedicated kiln/furniture for lead or cadmium.
Likely underfiring (formula too refractory for the cone, by limits/Stull, or flagged in the analysis) caps fitness at A2; a pyrometric cone that did not fall, as reported by you, caps it at A3 until refired.
Q0Firing · ok
No sign of underfiring.
Q1Firing · likely underfired
The formula probably will not melt at the declared cone — a porous surface does not seal.
Q2Firing · cone did not fall
The pyrometric cone did not fall in the reported firing; refire before trusting the piece.
Chemical durability of the glass, computed by code only: too little silica or alumina, or too much alkali for the cone = unstable (the metal is not locked in); a small deviation = borderline; high alumina or silica is a melting matter (axis Q), not leaching. An unanalysed material weighing 15% or more of the recipe makes the matrix undetermined instead of guessing.
Stable glassy matrixBorderline glassy matrixUnstable glassy matrixMatrix not computable
Chemical screening, not a laboratory report. Compliance of food-contact ware is only proven by a migration test (ISO 6486; ASTM C738).
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 an unstable matrix on Axis 2 — computed R₂O/RO above 0.45 with a leachable colourant (Cu/Co/Mn) at moderate or above, or stability failing in a computable matrix. May be used on the outer part of a utilitarian piece (foot, exterior); for food contact, run the migration test. (Firing maturity alone never lowers to this level.)
An oxide in the RISK (high) band on Axis 1; OR lead/cadmium on a piece declared DECORATIVE (with mandatory handling conditions: PPE and a dedicated kiln); OR high Cr₂O₃ under an oxidizing atmosphere on a decorative piece. Do not use on pieces that touch food. Axis 2 or 3 problems never lower to this level — they cap the grade at 2.
PbO > 0 OR CdO > 0 on a UTILITARIAN piece (any amount — the only metals with a migration limit in the norms) OR BeO > 0 in any use (IARC Group 1) OR Cr₂O₃ in the risk band under an oxidizing atmosphere on a utilitarian piece (Cr⁶⁺ likely). Reformulate before testing.
Percentages over the base glaze. Reference bands adopted by the platform, calibrated on real cases and specialist technical review — not legal limits (the norms regulate migration from the fired piece, in mg/kg, not recipe percentages). Normative references: ASTM C738 (leach test), Portaria SVS/MS 27/1996 (RDC 843/2024) and RDC 722/2022 (Anvisa).
| 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 for glazed ceramic ware (Brazil: Ordinance SVS/MS 27/1996, amended by RDC 843/2024; ANVISA RDC 722/2022 + IN 160/2022; 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 platform computes the 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) are estimated from it and enter as caveats. In the grade, a computed R₂O/RO above 0.45 with a leachable colourant (Cu/Co/Mn) at moderate or above caps the result at 2. A commercial frit with no declared composition is treated as stable (it is industrially insoluble by design), not as a failure.
The likely finish is estimated from the SiO₂:Al₂O₃ ratio (Stull Chart zones; a glossy, vitreous surface in the ~5–12 zone is best for food) and recorded as a caveat, not in the grade. 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.
In Brazil the norm that governs the glazed piece itself is Ordinance SVS/MS 27/1996 (technical regulation for glass and ceramic ware in contact with food). Item 4.3, in the wording given by RDC 843/2024 (in force since 1 September 2024), requires any ceramic, glass or metal ware that is enamelled or vitrified on the food-contact face to meet the limits below. RDC 722/2022 + IN 160/2022 are complementary: they cap the contaminant in the food, not what the ware may release. Screening also follows ISO 6486-2, ASTM C738, FDA CPG 7117.07 and the IARC carcinogen classification.
| Category | Lead | Cadmium |
|---|---|---|
Category 1 Ware that cannot be filled, or filled ware up to 25 mm internal depth — plates, shallow platters, tiles. | 0.8 mg/dm² | 0.07 mg/dm² |
Category 2 All other fillable ware — mugs, bowls, cups, pitchers up to 3 L. | 4.0 mg/kg | 0.3 mg/kg |
Category 3 Cooking ware and storage vessels over 3 L. | 1.3 mg/kg | 0.1 mg/kg |
Specific migration (item 5.2.4). Total migration (item 5.1.7): 50 mg residue/kg of water or 8 mg/dm², with an analytical tolerance of 5 mg/kg or 0.8 mg/dm². Extraction with 4% acetic acid, read by atomic absorption spectrophotometry — the equivalent international tests are ASTM C738 and ISO 6486-2.
These are limits for the fired piece measured in a laboratory — not recipe percentages. Keramoslab does not measure migration: the oxide-percentage screening is predictive and exists to tell you whether the piece is worth sending for testing.
Questions or technical feedback? Write to suporte@keramoslab.com.br.
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