Pottery is a popular art and craft skill not simply for its beauty, but also for its functionality. You can create anything in pottery – from a vase to a mug, a statue to a plate.
If you’ve spent hours to create something functional like a plate or mug, you probably intend to use it. In our modern society, a common use for plates and mugs is to set them in the microwave to heat up cold food or beverages.
So, is ceramic microwave safe? Most ceramics are microwave safe, but it depends on the clay and glaze used. If it’s a purchased piece of ceramic, check for a label that indicates whether it’s microwave safe. If you’ve made it at home, there’s an easy test to check for safety. Never microwave ceramics with metal rims or details.
Let’s go over the details of microwave safe ceramics, including an explanation of the ceramics that are not microwave safe, how to tell the difference, and what precautions to take when using ceramic kitchenware.
Microwave Safe Ceramics
Most of our dishware that we purchase at the store is made using ceramics. With people who choose to pick up pottery as a hobby, one of their first creations will likely be a bowl or other kitchenware item.
Because ceramics are so widely used in the kitchen, they’re generally microwave safe. This will vary, though, based on the clay used, the glaze used, and whether there are any metal components.
If your ceramics are made with porcelain, they’re great for use in the microwave. As long as your porcelain doesn’t have any metal rim or accent work, it’s good to go in the microwave.
Porcelain is one of the best ceramics for microwave use because it’s nearly completely non-porous, which means it won’t absorb all the heat the microwave will radiate into it.
Some stoneware ceramics are also safe for the microwave, but this will depend on how refined the clay is and what temperature it was fired at to finish the piece. The clay should generally be more refined and fired at a high temperature to make it microwave safe.
When clay is less refined, it’s more porous and susceptible to absorbing the heat. This creates a problem because as the ceramic absorbs liquid and heat, it starts to swell and pressurize, which leads to cracking and breaking.
You can always tell if your store-bought ceramics are microwave safe based on the label. There should be an icon of wavy lines (symbolizing the radiation of the microwave) or the words “Safe for Microwave Use” written on the bottom.
If there’s no label to indicate whether it’s safe for the microwave, don’t worry. We’ll go over a simple test you can run to ensure it’s safe for microwave use.
Why Are Some Ceramics Unsafe For Microwaves?
1. Porous, Less Refined Clay
As we mentioned above, ceramics that are made with a more porous or less refined clay are not safe for the microwave because they allow for more absorption of water and heat.
For example, if you place a mug made with porous clay (such as earthenware) filled with water in the microwave, those pores will absorb the water and store it in the tiny holes in the clay. As it heats up, the steam created from the heated water has nowhere to go.
When all that steam builds up within the walls of your ceramic, it starts to become highly pressurized. That’s when the ceramic item starts to crack or even explode.
This is why finer clays such as porcelain are ideal for microwave use, because they are far less porous and less prone to absorbing heat.
2. Toxic Glaze
Aside from the clay, you also have to consider the glaze used on the ceramic. If you purchased it at the store, you may not be able to tell. If you’re trying to microwave homemade pottery, however, you’ll know which glaze you used and can determine if it’s safe.
There are lead glazes, for instance, that you would never want to microwave. Other glazes can also give off radiation when microwaved, so it’s important to read the label of your glaze for food-safe ratings.
While these glazes may not have much of a visual reaction in the microwave, the heat will cause some of the toxic materials to leak into your food. So even though it may look safe to use, always check the label first.
3. Metal Components
The final unsafe factor to look out for in your ceramics is a metal rim or detail work.
Just as you would never microwave one of your silver spoons or forks, you’d never want to microwave a ceramic dish with a metal rim. The metal in the pottery would start to spark and create a huge risk of fire if microwaved.
Luckily, metal is usually easy to spot in ceramics. If you notice that the rim is shiny or there are shiny accents within the design of your ceramic, it’s best not to microwave that piece.
This can be common for higher-end dishware such as fine china sets which tend to use metal rims and detail work in the intricate designs, like leaves and floral patterns.
How To Tell If An Unmarked Ceramic Is Microwave Safe
While this test will tell you if your ceramic is safe for the heat, it won’t tell you if the glaze is safe. Only use this test for ceramics you are sure were finished with a non-toxic glaze and have no metal components.
Grab a mug you already know is microwave-friendly from the label and the mug you’re unsure of and want to test. Then, follow these easy steps:
- Fill each mug halfway (or a little more) with water.
- Place both mugs into the microwave next to each other.
- Make sure your microwave power is high and microwave the mugs together for one minute.
- The mugs will likely be too hot to touch, so use a potholder or kitchen towel to remove the mugs from the microwave.
- Carefully touch the test subject mug, then the water inside of it. If the mug is warm but the water inside is still cold, the pottery absorbed all the heat and it’s unsafe for use in the microwave. If the dish feels cool where there’s no water and the water is warm, the pottery did not absorb the heat and is safe to use in the microwave.
You can run this test on plates, bowls, or other ceramic dishware too. If the unmarked plate and microwave safe mug don’t fit side-by-side in the microwave, simply place the mug on top of the plate.
If the plate feels warm where the mug sat on top but cooler around the edges, it’s most likely microwave safe.
Once you have your results, it’s best to add some sort of mark or indicator for yourself so you know whether to use it in the microwave or not. You can make a note in permanent marker on the bottom of the ceramic, or use a label maker to print a label for underneath.
Precautions For Ceramics And Heat
Even though ceramics are usually safe to use in the microwave, precautions should still be taken when mixing your ceramics and heat.
Microwave ceramic dishes at intervals, allowing the dish a small break from the heat by stirring your food or liquid every couple minutes or so.
Never put your ceramic dish on an open flame. While they’re safe for use in the microwave or oven, they’re not intended for stovetop cooking. The only instance where it might be safe on an open flame is if the ceramic specifically states that it’s safe for stovetop cooking on the label.
You should never take a ceramic dish straight from the refrigerator and place it in a preheated oven or the microwave. This extreme change in temperature will cause the dish to crack or break apart.When it comes to oven safety, there are several other things to consider for ceramic use.
Most recipes and oven cooking instructions will state to preheat the oven first. However, if you’re planning to use a ceramic dish in the oven, it’s best to put it in at room temperature and allow the ceramic to heat slowly with the oven.
The slower change in temperature will help prevent cracking. Plus, the food will generally heat up at the same rate as the dish, so preheating won’t help the food cook faster anyway.
It’s also a good idea to avoid using flatter ceramic dishes such as trays in the oven as they’re more likely to crack while baking. Instead, choose a deeper ceramic dish such as a pot in the oven.
Whether you’re using microwave, oven, or even boiling water for heat, avoid any drastic changes in temperature. This is a good rule of thumb for all ceramics, as quick changes in heat lead to cracking.