You've just opened a can of soup or beans and are looking for a way to heat them up. You could use the microwave, but then you see that your glass jar is in the cupboard. Is it safe to put it in there?
For a quick answer, glass jars are actually safe to put in the microwave. Glass is an excellent insulator and poor conductor of heat. It's also totally inert—meaning it's not going to react with anything else, which means you don't have to worry about the jar exploding or getting contaminated by any chemicals from your food.
Glass isn't perfect though: it does conduct electricity (but not very well), so if you're trying to microwave something that has metal inside it—like an aluminum-foil covered bowl—the foil might get hot enough to start a fire when exposed to electromagnetic fields generated by microwaves. And while glass itself won't catch on fire under normal circumstances (I mean come on guys), if there is flammable stuff like oil or grease around then there's definitely risk of a fire happening (so be careful!).
Here are some other things you should know about glass:
The bottom line: Tempered glass is more expensive than regular glass, but it's worth the investment. It's also slightly thicker than non-tempered versions, so you'll need to take that into account when you're measuring out the jar for your project. However, not all glass is tempered.
The base should be marked with the manufacturer's recommended guidelines.
Another way to test whether your glass jar is microwave safe is to put a small amount of water in it and place it in the microwave for a few seconds. If the water does not boil, then you should be able to use the jar safely.
This will prevent the glass jar from breaking and spilling hot food or liquid all over your hands.
To remove the jar from the microwave, use an oven mitt or potholder to hold onto it while pulling it out with one hand. You can also simply let the jar cool down on its own before attempting to remove it.
If you're unsure of your jar's safety, check its base for any manufacturer's recommendations. You can also test your glass jar by placing a small amount of water in it and heating it on high power for several minutes. Let the jar sit for several minutes after removing it from the microwave before opening—this will allow any excess heat to dissipate safely.
The microwave is an incredibly useful appliance that can help you save time and energy in the kitchen. But if you're looking to microwave glass jars, there are some precautions that you should take. It's always a good idea to check the base of your jar for any manufacturer's recommended guidelines before microwaving it. You can also test your glass jar in the microwave with a little water before putting food in it - if everything goes well after doing this then all should be fine! Just make sure not to overheat anything too much because it may crack or shatter when exposed to high temperatures.