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.
| Glossary |
Metallic Glazes
Non-functional ceramic glazes having very high percentages of metallic oxides/carbonates (manganese, copper, cobalt, chrome). |
| 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! ASTM D-4236 DOES NOT establish that a fired glaze is food-safe or resistant to leaching. It is a standard for evaluating and labelling chronic health hazards associated with using the art material itself. It "applies exclusively to art materials packaged in sizes intended for individual users of any age or those participating in a small group". It "concerns those chronic health hazards known to be associated with a product or product component(s) when it is present in a physical form, volume, or concentration that in the opinion of a toxicologist has the potential to produce a chronic adverse health effect". It also admits that "since knowledge about chronic health hazards is incomplete and warnings cannot cover all uses of any product, it is not possible for precautionary labelling to ensure completely safe use of an art product" (referring to safe use of the art product, not food safety of the fired pottery made from it). It is interesting that one manufacturer displays this warning on pages relating to dipping glazes and accessory products (which are used by manufacturers): "Safety Warning: Tableware producers must test all finished ware to establish dinnerware status, due to possible variations in firing temperature and contamination." That being said, some manufacturers do test glazes and underglazes for lead and cadmium release (e.g. using ASTM C927/C738 to meet FDA dinnerware guidelines). For them, ASTM D4236 is not the evidence presented for dinnerware-safety evidence; separate fired-glaze testing is. For example, one brushing glaze label specifically says its “Food Safe” designation comes from lead/cadmium-release testing under ASTM C738-94. |
![]() PayPal | No tracking, No ads, No paywall, No transient content! Just organized, concise information constantly updated and improved. Was this helpful? Consider supporting me. |
Buy me a coffee and we can talk