Q. I’ve always thought it was safe to microwave foods in glass containers but the other day a friend told me not all glass is the same and some aren’t safe. She said a glass dish could explode! Well, I haven’t had that happen, some of my glass dishes have a microwave safe symbol on them but others have nothing and I’m wondering if it’s ok, can you microwave glass?
A. Glass is a fairly fascinating material. It’s made by heating ordinary sand (mostly made of silicon dioxide) until it melts – at about 1700°C (3090°F) – and turns into a liquid. When it cools it undergoes an inner transformation with something of a crystalline structure. But strangely even after cooling it never sets into a solid. It becomes a sort of frozen liquid, or what scientists refer to as an amorphous solid.
Glass is used everywhere in today’s world. It’s in and around our homes because it has all kinds of really useful properties. Not only is it transparent but it’s inexpensive to make, easy to shape when molten, fairly heat resistant when it’s set, chemically inert (doesn’t react with the things you put inside it) and it can be recycled over and over and over again.
Even if glass dishes don’t say they are microwave safe they likely are, as glass doesn’t leach chemicals into your food like plastics can. Glasses that are certified safe in the microwave will have a logo imprinted in them. If the glass doesn’t have the logo or is a cheap fragile variety, it’s not necessarily going to break when you put it in the microwave but it may break when you take it out as it cools.
While often safe for microwave use, glass may shatter with rapid temperature changes. I remember a microwaved coffee glass shattering after I had dropped and ice cube in to cool it down for quick drinking.
Watch out for metal rimmed glass, lead glass, or is fragile don’t put it in the microwave. Metals spark in the microwave and could damage it. Fragile glasses, perhaps like the thin cheap glass collectables gas stations used to give away, may not be very heat resistant so the food or drink temperature may shatter it.
Otherwise microwaving in glass dishes shouldn’t be a problem and it’s certainly better than zapping your food in plastic.