Soda-Lime Glass

Inert and non-leaching in food contact. Nothing migrates out of the glass itself, there is no coating or liner, and it does not react with acid, salt, fat or alcohol. The one real chemical caveat is not the glass but what is printed on it: cadmium and lead pigments have long been used in the enamel decorations fired onto the outside of drinking glasses. In June 2010 the CPSC recalled about 12 million McDonald's Shrek glasses made by Arc International because the exterior designs contained cadmium that could rub off onto hands. Exterior decoration below the rim is not a food-contact path, but decorated rims and heavily painted novelty glassware are worth avoiding for children.

The weak point. Soda-lime's expansion coefficient of 9-9.5 x 10^-6 /K limits it to a temperature differential of only about 100F / 55C before thermal stress can fracture it, so a hot dish onto a wet stone counter, a splash of cold water into a hot pan, or a frozen dish into a hot oven are all real failure modes rather than folklore. Bradt and Martens, writing in the Bulletin of the American Ceramic Society in 2012, called the margin of safety for soda-lime cookware "borderline" and not adequate for all household cooking. Boiling water into a thick-walled room-temperature glass is normally fine; steep gradients across a thin or already-scratched wall are not.

Assume soda-lime unless a maker says otherwise, since it is the default for drinkware, jars and storage. On bakeware, the case of the brand name is the practical tell: lowercase pyrex is the post-1998 US line and is tempered soda-lime, while all-caps PYREX means vintage Corning or European production in borosilicate. Consumer Reports' 2010 investigation established that Corning ran both glasses in its US plants well before the 1998 licence transfer, so even old US pieces are not guaranteed borosilicate. If a listing just says "glass" or "heat-resistant glass", that is soda-lime until the brand quotes an expansion coefficient.

Chemically it lasts forever; mechanically it is the most breakable thing in the cupboard. Annealed soda-lime breaks into large sharp shards, and existing nicks and scratches on rims and bases are where thermal and impact failures start, so a chipped jar or dish should be retired. Dishwashers are safe for the glass, though repeated cycles in soft water can etch a permanent haze into the surface.

The one genuinely and infinitely recyclable material in most kitchens: glass can be remelted without quality loss, and container glass is the stream municipal recycling is actually built around. Practice lags the theory - EPA put the US glass container recycling rate at 31.3% in 2018, with about 7.6 million tons of glass landfilled that year. Keep bakeware, drinking glasses and window glass out of the container bin; they melt differently and contaminate the batch.