Handmade mugs feel wholesome. But color comes from metal oxides — lead, cadmium, cobalt, chromium — and acids pull them out. Periodic scandals over imported ware keep the question alive. The thesis from migration research: well-formulated, well-fired glaze is effectively inert; risk concentrates in low-fired decoration, damaged surfaces, and acidic contents — all testable, all avoidable.

What leaches, and when

Standard testing soaks ware in 4% acetic acid for 24 hours; EU limits cap lead at 0.8 mg/dm² (flatware) and cadmium at 0.07 mg/dm². Market surveys find most compliant ware far below limits (Bulut, 2021, Wiley) — but outliers shatter them: Turkish market plates hit 4.14 mg/dm² lead, 5× the FDA cap (Yaman, 2013). Belgian experiments (Sciensano) show leaching rises with acidity (citric beats acetic below pH 3), temperature (2 h at 90 °C out-leaches 24 h at 20 °C), time, and — critically — glaze formulation, with some glazes releasing double others’. High release traces to three failures: underformulated glaze, underfiring that leaves lead unbound in the glass matrix, and overglaze decoration. A standing USDA/FSA program (NAL project) extends testing to cobalt, chromium, and repeated use, crazing, and microwaving.

The potter’s safety checklist

Use certified lead-free, cadmium-free glazes from reputable suppliers; fire to the glaze’s full maturity (underfiring is the classic home-studio failure); avoid lead/cadmium colors on food surfaces (exteriors and rims-free zones only); test with home lead swabs as screening, lab testing for selling; and retire crazed, etched, or dishwasher-clouded food ware — damage reopens the matrix.

The counterpoint: don’t panic, prioritize

Lead-free modern studio practice, fired correctly, shows negligible migration — the hazard is overwhelmingly vintage, imported-bargain, and hobby-underfired ware. Ceramic risks rank far below the dietary lead from old pipes or soil in affected areas. Perspective matters: test the flea-market pitcher, relax about the properly fired studio mug.

Takeaway

If you sell or gift food ware: buy tested glazes, fire to maturity, keep bright colors off interiors, and say so on your card. Safety, like glaze fit, is chemistry you can verify — and customers taste the confidence.