Plain-language definitions for the material-safety terms you’ll see across our reviews and guides. Reviewed by James Daniels, B.Sc, inorganic chemist and materials researcher.
Materials
- Borosilicate glass — A glass made with boron trioxide, which gives it a low coefficient of thermal expansion. That means it resists cracking from sudden temperature changes better than ordinary soda-lime glass, which is why it’s common in lab equipment and oven-safe bakeware.
- Soda-lime glass — The most common type of glass, made from silica, soda ash, and lime. Cheaper to produce than borosilicate, but more prone to thermal shock, so it’s less suited to direct oven-to-freezer temperature swings.
- Tempered glass — Glass that’s been heat-treated to increase its surface compression, making it several times stronger than untreated glass of the same thickness. It’s more resistant to impact, but when it does fail, it shatters into small, blunt pieces rather than large shards.
- Opal glass — An opaque, often white glass made by adding fluoride or phosphate compounds during production. Used in dinnerware for its solid color and durability.
- Vitrelle — Corning’s trademarked laminated glass, made by fusing three layers of opal glass together under heat. It’s the material behind classic Corelle dinnerware, and it’s notably chip- and break-resistant compared to single-layer glass.
- Pyroceram — A glass-ceramic material (best known from vintage Corning Ware) that combines glass’s transparency-manufacturing process with ceramic-like heat resistance, allowing it to go from freezer to stovetop without cracking.
- Stoneware — A dense, non-porous ceramic fired at high temperatures. Sturdier than earthenware, and commonly used for baking dishes and everyday dinnerware.
- Porcelain — A fine, translucent ceramic fired at very high temperatures, prized for its strength relative to its thinness and its smooth, non-porous surface.
- Bone china — A type of porcelain made with bone ash, giving it extra strength, a bright white color, and a slightly translucent look.
- Melamine — A hard plastic resin often used for lightweight, break-resistant dinnerware. It’s not microwave-safe and isn’t intended for direct contact with high-heat cooking.
- Crazing — A network of fine surface cracks that can develop in a glaze over time, usually from repeated heat stress or age. Crazed glaze can allow moisture, and potentially bacteria or leachable substances from an underlying glaze, to penetrate the surface.
Safety and regulation
- Lead glaze — A ceramic glaze formulated with lead compounds, historically used for its rich color and shine. Lead can leach out of an improperly fired or damaged glaze into food, especially acidic food, which is why lead content in dinnerware glazes is regulated.
- BPA (bisphenol A) — An industrial chemical used in some plastics and can linings. Regulatory agencies and manufacturers have moved away from BPA in food-contact plastics amid concerns about hormone disruption, and many products are now labeled BPA-free.
- Prop 65 — California’s Safe Drinking Water and Toxic Enforcement Act of 1986, which requires warning labels on products sold in California that expose consumers to certain chemicals, including lead and cadmium, above state-set thresholds. It’s stricter than federal limits in many cases, so we use it as a reference point even for non-California readers.
- FDA food-contact compliance — U.S. Food and Drug Administration rules governing what materials are allowed to touch food, and under what conditions. A material can be FDA-compliant for food contact without being tested for every possible use case, which is why we cross-check compliance claims against how a product is actually meant to be used.
- XRF testing — X-ray fluorescence testing, a common method (including the kind used by CPSC and independent labs) for detecting the presence of heavy metals like lead and cadmium in a material without destroying the sample.
- Food-safe — A general term meaning a material is considered safe for direct or repeated contact with food under normal use. It’s not a single legal certification; we always specify which standard (FDA, Prop 65, or a manufacturer’s own testing) a food-safe claim is based on.
- Non-toxic — A marketing term without one fixed legal definition in the U.S. When we use it, we mean a product has no known hazardous levels of substances like lead, cadmium, or BPA under the regulatory thresholds referenced above, not that it has passed a specific government certification.
Don’t see a term you’re looking for? Let us know at editorial@safekitchn.com and we’ll consider adding it.