Ceramics Monthly: What motivated you to write a technical book that focused directly on food-safe glaze recipes?
Bill Collins (left): As a chemist working with ceramic glazes, I kept encountering the same problem: potters genuinely wanted to make food-safe work, but there was no reliable, scientifically grounded resource to guide them. Most glaze books treated ‘food-safe’ as a label rather than a testable, measurable standard. Gabriel and I wanted to change that by bringing real lab methodology into the studio to give potters confidence that their work is truly safe, not just assumed to be.
Gabriel Kline (right): Bill just hit the nail on the head! As a studio potter producing work for registries and restaurants, I wanted to give myself and my clients peace of mind that the pottery I was producing was safe to use. I was frustrated, however, because I couldn’t find a standardized definition for what constituted a food-safe product. An early conversation with Bill about this “food-safe dilemma” parlayed into the research and testing that yielded a new standard of food safety in ceramics, and a resource for potters that is easy to understand, but is grounded in real science.
CM: How do you define “food-safe,” and what was the biggest misconception about glaze safety that you wanted to correct in your book? Were there any surprising discoveries made during your testing and research?
BC and GK: Food-safe, as we define it in the book, isn’t a feeling or an assumption, it’s a measurable outcome. A glaze is food-safe when it both resists pathogens due to physical flaws and doesn’t leach harmful levels of metals into food or drink under real-world conditions. We looked at established regulatory standards for metal migration limits—things like barium, chromium, cobalt, lithium, and other potentially harmful elements—and built our testing protocols around those thresholds. If a glaze couldn’t pass those benchmarks, it didn’t make our food-safe recipes section, regardless of how beautiful it looked.
The biggest misconception we wanted to tackle is the idea that if a glaze looks glossy and smooth, it must be food-safe. That’s simply not true. A glaze can appear perfectly intact and still leach metals at unsafe levels, particularly under acidic conditions like coffee, citrus, or vinegar. Visual inspection of the surface tells you almost nothing about the chemistry happening beneath it.
One finding that genuinely surprised us was how strong the correlation turned out to be between firing temperature and metal leaching. We expected temperature to matter, but the degree to which it mattered was more pronounced than we anticipated. Even relatively modest differences in firing temperature could meaningfully change a glaze’s leaching profile; a glaze that performed safely at one temperature could behave quite differently if under-fired. This has real practical implications for studio potters, because kiln temperature variation is incredibly common. It’s not enough to have a good recipe; you have to fire it correctly and consistently every time. That finding reinforced for us why we couldn’t just present recipes in isolation; we had to pair them with guidance on firing practice and application as well.
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Ceramics Monthly: What motivated you to write a technical book that focused directly on food-safe glaze recipes?
Bill Collins (left): As a chemist working with ceramic glazes, I kept encountering the same problem: potters genuinely wanted to make food-safe work, but there was no reliable, scientifically grounded resource to guide them. Most glaze books treated ‘food-safe’ as a label rather than a testable, measurable standard. Gabriel and I wanted to change that by bringing real lab methodology into the studio to give potters confidence that their work is truly safe, not just assumed to be.
Gabriel Kline (right): Bill just hit the nail on the head! As a studio potter producing work for registries and restaurants, I wanted to give myself and my clients peace of mind that the pottery I was producing was safe to use. I was frustrated, however, because I couldn’t find a standardized definition for what constituted a food-safe product. An early conversation with Bill about this “food-safe dilemma” parlayed into the research and testing that yielded a new standard of food safety in ceramics, and a resource for potters that is easy to understand, but is grounded in real science.
CM: How do you define “food-safe,” and what was the biggest misconception about glaze safety that you wanted to correct in your book? Were there any surprising discoveries made during your testing and research?
BC and GK: Food-safe, as we define it in the book, isn’t a feeling or an assumption, it’s a measurable outcome. A glaze is food-safe when it both resists pathogens due to physical flaws and doesn’t leach harmful levels of metals into food or drink under real-world conditions. We looked at established regulatory standards for metal migration limits—things like barium, chromium, cobalt, lithium, and other potentially harmful elements—and built our testing protocols around those thresholds. If a glaze couldn’t pass those benchmarks, it didn’t make our food-safe recipes section, regardless of how beautiful it looked.
The biggest misconception we wanted to tackle is the idea that if a glaze looks glossy and smooth, it must be food-safe. That’s simply not true. A glaze can appear perfectly intact and still leach metals at unsafe levels, particularly under acidic conditions like coffee, citrus, or vinegar. Visual inspection of the surface tells you almost nothing about the chemistry happening beneath it.
One finding that genuinely surprised us was how strong the correlation turned out to be between firing temperature and metal leaching. We expected temperature to matter, but the degree to which it mattered was more pronounced than we anticipated. Even relatively modest differences in firing temperature could meaningfully change a glaze’s leaching profile; a glaze that performed safely at one temperature could behave quite differently if under-fired. This has real practical implications for studio potters, because kiln temperature variation is incredibly common. It’s not enough to have a good recipe; you have to fire it correctly and consistently every time. That finding reinforced for us why we couldn’t just present recipes in isolation; we had to pair them with guidance on firing practice and application as well.
Photos: (left) Shan Wells; (right) Brian McCarthy
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