Yes, you can microwave most glassware in certain circumstances. But before you try to heat your next glass of water in the microwave, be aware that doing so comes with important safety precautions and warnings. Let’s talk about what happens when you put glass in the microwave, along with how to be safe while heating that plate of glassware in the microwave oven.
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Can You Microwave Glass?
If you are careful and select the correct container, your glass will be safe from shattering. It’s also important to consider how long you are heating your glass when deciding on whether to use a microwave.
Reheating food using containers made from ceramics such as porcelain or Pyrex is generally considered safe if these conditions are met. Use low power settings (such as 50%) to avoid overheating your food or drink.
How Do You Microwave Cold Glass?
If you put cold glass in a microwave, it may crack or shatter. This is because a large amount of thermal stress builds up inside of it making it expand its volume.
The same thing happens if you put hot glass in a microwave. It heats up too quickly and expands so much that it breaks apart.
Instead, if you want to reheat something with glass, make sure it’s room temperature first. Then heat it at 50 percent power for five minutes on each side—just enough time to warm through without breaking apart from excessive heat buildup.
Does Glass Melt In the Microwave?
By and large, glass doesn’t melt in a microwave. It can become warm, but it takes quite a while to heat up and will usually not suddenly explode.
Glass is made up of tiny molecules that do not move around easily at room temperature. In fact, glass has one of the highest melting points of any standard material: about 1,600 degrees Fahrenheit!
These tiny molecules don’t have enough energy to release as heat in a standard kitchen microwave. Instead, microwaves send vibrations into an object that causes some areas to gain energy and others to lose it.
The glass will only start to melt when there is not enough energy left over for vibrating molecules. This means that you would need a very strong magnetron (the part of your microwave that generates microwaves) or cook food for several hours to melt glass.
So no, glassware will not melt in a microwave oven.
Check The Label of Your Glass Container
When it comes to microwaving your glass containers, there are a few things you should pay attention to in terms of labeling. First, if your container is labeled microwave-safe or something similar, then yes, you can generally take it out of the fridge and put it in a microwave with little to no risk. Usually, these labels will be located on the bottom of the glassware.
The label could also say something like “For stovetop and oven use only” or “Not microwave safe.” Both statements mean that putting your glass container in a microwave probably won’t end well for either your dish or you. Don’t take any chances!
However, there may be no labels on your container.
What If There’s No Label?
Here’s another safety factor to consider: glass containers often don’t have any sort of identifying information. It’s up to you to make sure that what you’re microwaving is microwave-safe.
If there isn’t a label or if it looks strange, don’t assume it can go in your microwave. While manufacturers usually list safe handling instructions on their packaging, not all manufacturers do so.
Types of Glass Containers Safe to Use in the Microwave
As stated above, there are some types of glass containers that can be used safely in microwave ovens.
Is Heat Resistant Glass Microwave-Safe?
Heat-resistant glass is safe in the microwave. The same properties that make it heat resistant also make it microwave-safe, so you can put your heat-resistant glass dishes and containers into a microwave oven without worrying about them breaking or exploding.
However, just because something is microwave-safe doesn’t mean it’s necessarily healthy to eat out of. Be sure to check food labels for cooking instructions before microwaving anything in your heat-resistant glass dish.
Are Ceramic Baking Dishes Microwave-Safe?
The best ceramic baking dishes are typically made from stoneware and will come with a microwave-safe label. Stoneware is safe to use in microwaves. This makes it perfect for cooking food, but it also means that you can use your dish to warm up leftovers or reheat soup or tea. There’s no need to worry about stoneware causing damage due to its ability to evenly heat across its surface.
Are Glass Casserole Dishes Microwave-Safe?
Since these containers are made of a material that won’t interact with heat, you can use them to cook or reheat food as you would any other microwave-safe dish. No need to worry about shattering your casserole dish in the microwave!
Is Corningware Glass Microwave Safe?
Yes, it is safe to use Corningware glass in the microwave. In fact, Corningware products have an accompanying microwave-safe logo to make it easier for you to identify these products. Most are even oven and dishwasher-safe as well!
Is Pyrex Glass Microwave Safe?
Pyrex is a brand of clear, unbreakable glass bakeware. Pyrex is one of the few manufacturers that can consistently withstand the high temperatures in a microwave oven and is still made out of borosilicate glass.
Because it’s heat-resistant, you can use it in the microwave to make hot foods without fearing that your Pyrex will crack. All varieties of Pyrex are safe to use in microwaves.
Are Glass Jars Without Silver or Gold Rims Microwave-Safe?
Microwave-safe glass jars are few and far between. If you’re in a pinch, however, there are some types of glass that can handle high temperatures—just don’t use them for hot or boiling foods. If they don’t have silver or gold rims around them you should be fine if you’re just quickly heating something up for a minute.
Is a Glass Bowl or Plate Microwave-Safe?
Glass bowls and plates are generally microwave safe. Make sure there aren’t any cracks in your glassware that could cause it to shatter when heated. If you’re microwaving a glass bowl or plate, you should use a lower power setting than you would for plastic or ceramic dishes.
This will prevent heat from building up too quickly and causing your glass to crack or break.
Related: Can You Microwave Plastic?
Glass Items That Should Never Go in Your Microwave Oven
Some glass objects are easily broken and should never go in the microwave. A problem that can occur when you microwave certain glass is that they break due to uneven heating. The bottom half of the glass will heat up faster than its top half because it’s exposed to direct contact with your microwave’s hot airflow.
The same goes for items made from colored glass such as stained glass and marble. If there’s any doubt about whether an item is microwave safe, don’t risk it! It’s better to play it safe than have an accident that ruins your meal or ruins your microwave.
Certain pieces are much more likely to get broken during microwaving. Glassware with tiny air bubbles trapped in it is one of these types. Heat can cause these air bubbles to expand and become larger, sometimes pushing through the glass and making cracks.
What about glass items with metal trim on them, like a cup with a gold ring around it?
In general, you should avoid microwaving items with metal trim. This is because the metal will heat up and cause a thermal shock in your microwave.
Metal also conducts heat very well and can cause hot spots in your glass item, especially if you’re microwaving your food or drink for an extended period. The longer you microwave these kinds of things, the greater their chance of breaking.
What about microwaving frozen glass?
Heating frozen glass can make it shatter. This is because freezing an object causes it to undergo contractions, which in turn causes its volume to decrease. When you heat an object that’s frozen, it causes its volume to increase considerably and make things more fragile.
If you want to heat something without worrying about cracks, let it thaw out first before putting it in the microwave. Wipe the sides of it down to get all of the excess moisture off or any frost that may be left then it should be fine.
Give Your Glassware the Microwave Test
You should only do this if you have a good idea that it will be fine, but you need to confirm it with your particular microwave. If you’re pretty sure it’s not going to work, then don’t do it.
Microwave it for one minute. It is not microwave-safe if it’s too hot when you touch it.
Avoid testing things that have a metal ring around them. Ceramic and porcelain are usually fine, but they will still heat up a little when you put them in the microwave.
If you open the microwave and you can feel the heat coming off of the glass, and you can tell it’s too hot to touch right now, the item is probably not microwave-safe. If it is slightly warm, but you can reach your hand in and pick it up without feeling like it will burn you, you should be fine.
Use caution and common sense when handing glass that may be hot.