Ever excitedly pull your hot chocolate out of the microwave, only to drop the mug because it’s scorching hot, while the drink inside is still… well, kinda lukewarm? We’ve all been there! It’s one of those kitchen quirks that leaves you scratching your head.
Why does some pottery get so incredibly hot in the microwave, while other pieces stay perfectly cool?
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Turns out, there’s a fascinating scientific reason behind this microwave mystery, and it largely comes down to one key factor: water absorption.
The Absorbent Truth about commercial pots
- Commercial vs. Handmade: Mass-produced pottery is typically vitrified, meaning it’s fired to a point where the clay becomes dense and non-porous. It doesn’t soak up much moisture, if any.
- Clay for artists, on the other hand, is sometimes less vitrified and can be slightly porous. This means it can absorb small amounts of water, especially after washing. Check those absorption rates in your clay particularly at cone 6.
- Microwave Magic: Microwaves heat food by exciting water molecules. If your mug has absorbed water, the microwave will heat that water within the clay itself, making the mug hot. Commercial pottery, being less absorbent, tends to stays cooler.
Commercial pottery, lacking this internal water, simply doesn’t have much to heat up, so it stays cooler.
Beyond Water: Other Factors That Can Heat Things Up
While water absorption is the main culprit, a few other things can contribute to a surprisingly hot mug:
- Hidden Metals (Usually Not): You might have heard that “metals” in the clay cause heating. Generally, this is a myth for everyday ceramics. However, if your pottery has actual metallic glazes like lusters (like gold or silver accents), those definitely shouldn’t go in the microwave anyway – sparks will fly!
- Crackle Glazes: If your glaze has tiny cracks (a common occurrence called “crazing”), water can sneak in there, leading to absorption of water and heating of the clay body..
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So, Is It Safe? And How Can You Tell?
While a scorching hot mug isn’t usually a safety hazard, it’s definitely uncomfortable to handle! If you’re ever uncertain about whether a particular piece of pottery is microwave-friendly, there’s a simple test you can perform:
Place the pottery you’re curious about in the microwave alongside a separate, microwave-safe glass or ceramic mug filled with plain water (that water is crucial, by the way – never run a microwave empty!). Then, microwave both on high for one minute. After the minute is up, carefully check both items. If your suspect pottery feels significantly hotter than the water, it’s a good indicator that it’s absorbing heat and might be better reserved for cold beverages or uses outside of the microwave.
Understanding your pottery’s properties can help you avoid those painful hot-mug surprises and keep your hands happy!
Want More?
For Flux Sake ep. 82: Why do pots get hot in the microwave? is hosted by Matt and Rose Katz of the Ceramics Materials Workshop along with Kathy King of the Harvard Ceramics Program. Together they answer your burning questions about clay and glaze. In each episode they answer listener submitted questions in a comical, but also insightful way. This show will have you laughing and learning about glaze chemistry the chemistry behind ceramics in no time. New episodes typically drop every 2 weeks.
Ready to dive deeper?
Loved learning about ceramic glazes? Want to go even deeper? Check out our Workshops & Courses, now available in Spanish, or YouTube Channel where Matt breaks it all down, myth-busting and Stull chart included!
