Are Glass Containers Oven Safe? [Here’s How To Tell]

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Glass dishes and containers are true multitaskers in the kitchen. In theory, you can use one to bake, then transfer into the freezer, defrost and reheat in the microwave, and pop into the dishwasher when it’s all said and done.

But, are glass containers oven safe? Is it true for all of them, or do they have to be special?

Today, we’ll talk about this topic. You’ll get to know how to recognize oven-safe glass, how to use it safely, and how to shop and care for it. Let’s get straight to it.

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How are oven-safe containers labeled?

Most containers are clearly labeled these days. You can either find all the info when shopping online, or they will at least come with a little piece of cardboard that lists all you need to know. 

If they are missing, look at the bottom of the dish. You’ll either find an etching or a sticker. The symbol you’re looking for will most likely resemble a steaming bowl of soup. It can also be a miniature oven with vertical squiggly lines (horizontal ones are for the microwave). 

What’s in the name: oven-safe vs ovenproof

In some cases, the difference is simply in location. In the UK, glassware is more likely to be marked as ovenproof, while in the US oven-safe is more common. 

However, there is another, bigger difference, especially noticed when you’re shopping for glass containers from the same manufacturer. Ovenproof will mark that these containers can handle higher heat than the oven-safe ones. 

Other signs

Just because glass is rated as oven-safe, that doesn’t have to transfer to the whole container. Sometimes, it’s just the question of whether the piece in your hands is well-made or not. Always look for the signs of structural damage as well as if the glass is significantly thinner in certain areas. 

Other things to look for are “accessories”. Some (designer) brands like to go above and beyond. Adding silicone handles or sleeves is great and useful, but metal attachments are not. Not all metal is oven-safe, and it can lead to thermal shock (more on that later). 

How to tell if a vintage or second-hand glass container is oven-safe?

This can be tough, but slightly easier if the container was made by a well-established brand.

Check the dish for logos first. If you don’t recognize the name, don’t worry. A lot of companies change their names and a simple search will tell you if they did some rebranding or were bought by another company.

Some companies will have galleries and archives that may help you. If not, reach out to them through phone or e-mail. Be ready to provide them with photos from different angles so they can identify the dish.

Or, reach out to the internet community. Many social media platforms have groups with people who collect vintage and antique kitchenware. There’s bound to be someone who can help you with this conundrum.

What’s tempered glass?

Tempered glass gets its name from the manufacturing process that includes controlled thermal and chemical treatments. This process produces very tough glass, that’s often used to protect things, ie the screen of your phone. 

In the world of food, it’s often used for restaurant plates and drinkware, bakeware, and even oven doors. 

Containers or baking dishes made from tempered glass are heavy, durable, and oven-safe to at least 400 degrees Fahrenheit. They also have a slightly better thermal shock resistance. 

What’s borosilicate glass?

Borosilicate glass contains boron trioxide which greatly impacts its response to heat. It has a low coefficient of thermal expansion, which makes them more resistant to high heat and thermal shock. 

This type of glass is also often used in the service industry, as well as the home in form of baking dishes, measuring jugs, and drinkware meant for hot drinks. 

Containers and bakeware made from this glass tend to be a bit lighter, but they can often withstand the heat of up to 450 degrees Fahrenheit. 

What makes glass containers shatter?

Thermal shock and direct heat. 

There are certain types of glass dishes that can be used for cooking on a gas or a halogen stove, but they are made especially for that job. Most containers and glass baking dishes can’t handle direct high heat. 

They also can’t handle temperature fluctuations, ie they can’t go directly from the freezer into the oven or vice versa. Temperature changes make glass expand and contract. Introduce that to bakeware that is uneven in shape and thickness, and you will have each section reacting differently to changes in temperature. It loses its structure and cracks are soon to follow. 

Microfractures are a problem as well. They happen when you bang glass against something, and they only grow over time. 

How to prevent glassware from shattering

Since high temperatures and temperature fluctuations are the problem, staying away from them is the solution. Here’s how to do it.

  • Never use the dish under a broiler or on the stove. They are a direct source of high heat and will shatter it straight away.
  • Always preheat the oven first. Especially if you have a newer oven with a fast preheat setting. Even older models tend to start at high heat and then lower it when you start baking.
  • Never leave the bottom of the dish bare. When baking chicken or a roast, always add a sauce or some stock.
  • When you take the dish out of the oven, always place it on a silicone or cloth potholder. A wooden or cork trivet is fine as well but never place it directly on the counter.
  • Don’t put a hot dish in the fridge or freezer. Not only will it destroy the texture of the food, but it will shatter the dish as well. Let it cool down to room temp first.
  • Don’t put a frozen dish in the oven or microwave. Defrost in the fridge (food safety first), then leave on the counter to come to room temperature. 
  • Never rinse a warm or hot dish with cold water. Just as well, don’t rinse a cold dish with hot water either. Also, leave it to come to room temperature before loading it into the dishwasher. 

How to shop for oven-safe glass containers

It would be best if you could shop in person for glassware, full stop. That way, you can pick each piece up and see if it feels flimsy. If it feels flimsy, it’s usually not worth it.

But, if you’re shopping online, the product description is the only thing you can rely on. Here’s what matters.

  • Borosilicate and/or tempered glass.
  • Temperature. 400 degrees Fahrenheit is great and will do for most of your baking needs. 350 is fine as well and will work for most cake and casserole recipes. 450 is ideal. 
  • Weight. Compare to glass containers that are not oven-safe, these should be much heavier.
  • Reviews. Look for both good reviews from people who have been using the containers for years and bad ones from recent buyers.

How to care for glass bakeware

Most glass bakeware is dishwasher-safe as well. The same goes for regular food containers that claim to be oven-safe. So, the washing will never be a problem as long as you allow the container to cool down a bit first.

However, storage and handling are another story. Bumping into cabinets and other dishes may cause tiny fractures. Those fractures may grow into something more serious with regular exposure to heat.

Store your glassware somewhere where it’s comfortable for you to reach. This will provide you with a firm grip and full control of movement.

If you have multiple pieces, place their lids or sheets of silicone or rubber between them, especially when stacking. Glass is smooth and chances are that something may slip. The lids will give some traction if something goes wrong.

Finally, avoid using metal utensils. Always opt for nylon or silicone. 

FAQ

Can I use a glass container directly in the freezer, dishwasher, to microwave after baking?

Not directly. As mentioned, sudden temperature changes will shudder the glass.

However, as long as you follow the instructions above, you can use the same dish to bake, freeze, defrost, and reheat with no problems.

Does the shape matter?

The shape matters when you’re baking, but not if the container is more oven-safe or not. The square corners provide more crispiness, while round and oval dishes don’t.

My glass container broke. Now what?

You can’t use it in the oven anymore even if you repair it. Probably not in the freezer or microwave as well.

You can put it back together (if you haven’t lost any of the pieces) with bonding super glue. Still, you can only use it for dry or pantry storage from now on.

Or send it to recycling.

Are glass containers and bakeware worth it?

Okay, they are a little bit temperamental and require a lot of careful handling. But, in the end, it’s worth it. 

Glass containers are versatile and non-toxic. They are easy to clean, allow you to see what’s happening with your food while it’s cooking, and retain heat for longer. And, as long as they don’t shatter, they will last a lifetime and then some. 

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