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The manufacturer warns that these cone 6 metallic glazes are not food-safe. That being said, many potters use them on food surfaces anyway. This can be deliberate or just because the warning label gets ignored, the product has no webpage or the QRCode on the bottle is not clear enough to scan. To demonstrate I did an overnight lemon juice immersion on the bottom end of this tile. Then I washed and thoroughly dried it. The amount of dissolution is amazing! Metallics are made using manganese, nickel, cobalt, chrome and iron - which of these would you like in your diet? To get a good effect 20-40% metal oxide is required.
These cone 6 porcelain mugs are hybrid. Three coats of a commercial glaze painted on outside (Amaco PC-30) and my own liner glaze, G2926B, poured in and out on the inside. When commercial glazes (made by one company) fit a stoneware or porcelain (made by another company) it is by accident, neither company designed for the other! For inside food surfaces make or mix a liner glaze already proven to fit your clay body, one that sanity-checks well (as a dipping glaze or a brushing glaze). In your own recipes you can use quality materials that you know deliver no toxic compounds to the glass and that are proportioned to deliver a balanced chemistry.
Glossary |
Metallic Glazes
Non-functional ceramic glazes having very high percentages of metallic oxides/carbonates (manganese, copper, cobalt, chrome). |
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URLs |
https://www.astm.org/d4236-94r21.html
ASTM D-4236 - Standard Practice for Labeling Art Materials for Chronic Health Hazards - It is not what you think! |
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