r/Physics • u/Dear_Mycologist_1696 • 1d ago
Image Chipped mug is getting extremely hot in microwave. I’d it the chip’s fault?
My favorite mug was recently chipped, and ever since it happened I noticed this mug, the handle in particular, becomes untouchably hot after 20 seconds in the microwave. My first thought is water has been absorbed into the ceramic through the unglazed chip, and this water is allowing the ceramic to better absorb (?) the microwaves and become heated before the liquid in the mug. Second thought is that I rarely microwave anything in a mug, so maybe all ceramic overheats in microwaves and I just noticed it for the first time in my forties. Could this chip lead to the mug handle getting exceedingly hot in the microwave?
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u/CryptikTwo 1d ago
You answered your own question. Ceramics are incredibly porous that’s why they are glazed.
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u/Eriksrocks 1d ago
Not entirely glazed though - in OP’s photo it looks like the bottom edge/rim of the cup isn’t glazed. So it should be just as porous as the chipped surface, right?
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u/Testing_things_out 1d ago
Not sure why everyone is piling on the idea that it is because of the glaze removed by the chip.
Just take your glazed ceramics and put them in the microwave. It takes less than a minute and you'll see that glazed ceramics get hot from microwaves.
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u/CryptikTwo 1d ago
Nobody said they won’t get hot In the microwave, the added moisture simply makes them heat up faster.
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u/fckcgs Condensed matter physics 1d ago edited 1d ago
Probably, yes. Also your explanation is pretty much correct. Your mug is glazed so normally it doesn't absorb water. Now that it is chipped, it does. The whole point of a microwave is, that it heats more or less ONLY [*] water, since it is a polar molecule, so the microwave makes use of the fact that water is slightly positively/negatively charged on either end and then with the right frequency makes it tur back and forth, back and forth. This vibration is then what heats up your food or your drink.
Ceramic normally shouldn't contain (much) water, so it won't heat up in a microwave. But since your mug drew water inside, it will now heat up as well. I'd recommend not using it in a microwave anymore but good to use otherwise.
Cheers
[*]: edit because of discussion in the comments: this is technically not true, but to describe how a microwave heats food or a broken mug, this simplification is really good enough.
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u/Philipp_CGN 1d ago
Probably not worth the effort (especially if you don't even use the mug for microwaving something anyway), but would it be possible to dry the ceramic and then repair the glazing somehow?
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u/fckcgs Condensed matter physics 1d ago
Should be possible, yes. Leaving it in the oven at low heat should accelerate the drying and then reglaze. Could be done if there is significant emotional value of the mug. But in reality, even using it in the microwave should probably not do any harm, it will just get hotter than before it was chipped as OP said.
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u/no_choice99 1d ago
Nope. A microwave oven heats up pretty much anything, it isn't particularly setup to heat up better water than anything else. But yeah, reddit loves to upvote common misconceptions, so be it.
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u/paarshad 1d ago
You’re both a little right? It targets polar molecules and water has strong polarity but it’s not the only polar molecule.
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u/fckcgs Condensed matter physics 1d ago
Thank you. This is correct. It also depends on the frequency, it needs to be somewhat correct as in not way too low or too high, but a microwave doesn't need to be exactly taylored to the absorption maximum in water. Indeed we also want to penetrate the food with the waves, so the actual frequency is significantly lower than what would be needed to excite the water molecules. We want to have the food homogenously heated and not only the "skin" after all.
But yes, I admit my response was a simplification and I don't know how water compares to other polar molecules exactly. However, water is usually abundant in food and my initial comment is not wrong entirely.
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u/no_choice99 1d ago
No, the person I was responding to was wrong on saying ''it heats more or less ONLY water''. This is just bs and wrong, despite the 50 (and rising) upvotes and my 20 (and increasing) downvotes.
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u/Aquamans_Dad 1d ago
It definitely heats polar molecules (and ions) directly through dielectric heating while the heat imparted to polar molecules and ions causes indirect heating of nearby non-polar molecules is my understanding.
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u/Unbegxbt 1d ago
no, the explanation the other reddit left seems to check out, you also happen to be the one that isn't explaining just stating something
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u/therift289 1d ago
Microwaves heat up anything polar, including anything with hydroxyl or amine moieties (like fats, carbohydrates, and proteins). Water is particularly polar, so it gains quite a bit of energy in a microwave, but it also has a very high heat capacity, so it heats slowly. Microwaves will generally increase the temperature of water-poor regions of food (such as fatty areas or dense carbohydrates) much more quickly than they heat really wet regions.
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u/kyrsjo Accelerator physics 1d ago
Fats aren't particularly polar? And that's pretty much why its not water soluble.
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u/therift289 1d ago
Polar regions vibrate and twist under a changing field even if the nonpolar regions aren't very affected. Fats have polar regions that vibrate in a microwave, and the nearby nonpolar regions with low heat capacity will rise rapidly in temperature as a result. Microwaves don't care about the net dipole of a large, flexible molecule; they interact with local dipoles wherever there are sufficient degrees of freedom to allow for rotation.
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u/elperroverde_94 1d ago
My first thought was about the chip absorbing water too, but the bottom of those mugs is never covered in ceramic (that's why it can be used to sharpen your knives). So the chip absorbing water doesn't makes sense to me.
Moreover that wouldn't explain why the handle go so hot in particular.
On the other hand, I cannot think about other reasons why the behavior should change after the chipping
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u/piecat 1d ago
The handle in particular gets hot because it is a closed loop.
Microwaves are EM waves with a time-varying magnetic field component, and changing magnetic fields induce voltage in conductive closed loops per Faraday's law.
This can also happen in MRI, which is why technologists put so many pillows and pads on a patient, and between their body arms and legs
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u/schwar26 1d ago
I think it’s some sort of bias.
Granted we can’t know for sure if it’s vitrified to .5%, there’s almost no reason it wouldn’t be.
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u/frontpage2 1d ago
As a potter amd materials scientist, there may be a few explanations, most of which are mentioned.
As you guessed, water is the most likely culprit if it went from being cool in the microwave to scalding after the chip. And the chip might be a symptom itself, if heat stresses have produced microcracks in the glaze and clay body, then this might have caused the chip (or made that area prone to chipping if you tapped it on something). So the whole mug, including the chipped area, may be letting in water.
One test can be to take the dry mug, pour boiling water into it, and then just let it sit on a paper towel. See if the paper towel gets wet after a few hours or overnight. You could also use dye, but dye molecules are larger so might not penetrate and travel.
I've actually seen this in a white mug. I could not see the cracks to the naked eye, but liquid seeped out of the handle, so clearly the cracks were there.
Different clays and firing temperatures will also affect how porous the final clay body is. The higher the firing temperature, the more glass-like the material becomes and the clay body is considered vitrified. Imagine fine porcelain that looks translucent and glass-like, because essentially the fine clay has been fired hot enough for it to become a breath from being glass. Now think of Terra cotta, which is fired at low temperature. It is super porous and moisture holding.
Glaze is very glass-like. It is essentially a layer of glass on the clay body. But, not all glaze is created equal. Some glazes will actually quickly get hot in a microwave due to the composition with various metallic oxides and minerals. So, if you were truly oblivious and the handle has always gotten hot, it could just be a glaze suseptible to microwave heating.
Also, glaze is formulated to be fired to certain temperatures and used on certain clay bodies. If there is a mismatch this can also lead to cracks which can let in water.
Finally, you asked about the ring on the foot being unglazed. This is where the mug is sitting on the kiln shelf, and it can't have glaze when being made or it would stick to the shelf upon firing. There are some techniques where you can glaze a whole piece, but it is more complicated and just leaving part unglazed works great.
This ring is usually less porous than other parts of the clay body because this area has been more compressed and finished since the manufacturer knew this spot would be bare. So although it isn't glazed, it would absorb significantly less water than the chip would, and also less than microcracks that penetrate through the glaze into the clay body.
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u/thehobosapiens 1d ago
No, not the Planet Express mug!
Hermes will never approve a new one!
He should bite my shiny metal ass!
.(I'm 40 percent microwave baby!)
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u/3weewilly3 1d ago
Certain color ceramic glazes heat up because of the metallic oxides that give them the color. I had a cup with a blue handle that would burn you after going through the microwave.
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u/ahf95 1d ago
Okay, while we’re at it, I have a related question. I have some plates that do this same thing (pretty much all of my ceramics do it after enough years), but these plates in particular have started to show this spiral pattern throughout the middle/flat regions, and they really absorb the microwaves a lot. Why did the spiral formation appear, and do the plates that have become spiraled have some internal orientation of things (water molecules, parts of the ceramic matrix) that prime them for easier absorption of microwaves?
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u/AbstractAcrylicArt 1d ago
When plates are formed - either on a potter’s wheel or in a mold - they often develop subtle spiral or circular “memory lines” in the ceramic body. During firing, shrinkage and glaze tension lock these orientations in, even though they’re hidden at first. Over years of heating, cooling, and washing, the glaze develops microcracks that let in water and dissolved salts. These substances concentrate along the original stress or tooling lines, making them reappear as visible spiral patterns. When the plate goes into the microwave, those slightly wetter regions absorb more microwave energy than the intact ceramic, so the spirals “light up” as hot spots and the plate feels like it’s strongly heating.
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u/jgmoxness 1d ago
The color treatment on the handle and mug may contain metal which the microwave heats. But that doesn't explain why it started only after the chipping.
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u/THEDrunkPossum 1d ago
Everybody answered already. I'm here to compliment the Planet Express theme. Good News, nobody!
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u/Prestigious_Boat_386 1d ago
I have one mug without a chip what gets extremely hot and others that are just fine. I just use the overheating mug for already hot things.
If it was the chips fault i feel like it would be more hot near the bottom, is that the case? At least when the chip was new.
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u/RedRedditor84 1d ago
Technically the microwave is heating your mug up. Try some experiments with it unplugged and i theorise it won't heat up despite the chip.
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u/John_Hasler Engineering 1d ago
Many ceramics are slightly porous but glazing is not. The mug has probably soaked up some water through the chipped area. This water is then absorbing the microwaves and heating up.
This could result in the mug exploding.
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u/FizzicalLayer 1d ago
All these suggestions and not one that is simply "Use another container to heat the beverage, then pour in cup."
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u/FlameInTheVoid 1d ago
This is about the physics, not how to fix the problem.
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u/FizzicalLayer 1d ago
Heh. Always some Smart Boy "acktuallly"ing their way to relevance. The following quotes from this thread contradict you:
"Well, off to Etsy I go for a replacement."
"I'm not a pottery expert or anything, but if you're willing to try, I'm sure you could bake the mug for a while and just recoat that chipped section with some more sealer."
"Leaving it in the oven at low heat should accelerate the drying and then reglaze."
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u/Mindmenot Plasma physics 1d ago
Good theory but is water actually ever in contact with the bottom chip?
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u/Hatedpriest 1d ago
Does it get washed, or is there humidity?
These things are fired, they have like 0% moisture in them after glazing.
If OP lives where relative humidity is >10%, the mug is now not 100% moisture free.
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u/boabey 1d ago
Good news everyone! I believe the heat being generated on this planet express mug is likely the components of the mug are made from antimatter. The chip has distorted the molecular structure and the microwaves excite them to a point where a new big bang will explode from said chip however your mug hasnt recieved sufficient radiation to start the chain reaction.
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u/UpperCardiologist523 1d ago
Probably not related, but i tried to microwave my WoW mug, and found out the handle became hot. It has metal inside it and i am lucky i didn't ruin it.
Do you have a magnet or something, to check? But weird that this didn't happen before if you have used it in the mw before.
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u/sevlonbhoi1 1d ago
its chipped from outside, inside is still glazed so water is not the cause.
I think its the same reason why you will see sparks in pointed metal things in microwave.
Chipping created sharp edges where the charges are getting concentrated making is the whole mug hot. Before chip there were no sharp edges in mug because of which the mug takes long to heat up.
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u/therift289 1d ago
If they've ever washed the mug or put it in a sink, then water has absolutely penetrated the ceramic through the chipped region.
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u/sevlonbhoi1 1d ago
You see that circular ring on the base of ceramic mug. That is the place from where its detached during manufacturing, that part is never glazed in ceramic mugs.
If water could penetrate during washing, it would have happened long back.
Fun fact: You can use that unglazed base to quickly sharpen your knife
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u/BobKickflip 1d ago
This is my thinking too. Was in a shared house where one flatmate saw another flatmate putting a metal spoon in there and low key panicked as we all thought you shouldn't put metal in them, but he searched online and we found that yep, it's the points of the fork that are bad.
I'd be tempted to leave the mug to dry for a month, then try microwaving it again
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u/sevlonbhoi1 1d ago edited 1d ago
I find it funny seeing my house guests panic when i put metal utensils inside microwave. Most people think that its going to explode within seconds bringing down the house.
Tells you that even educated adults need some basic science education.
I have been using metal inside my microwave for more than a decade now.
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u/slumgrace 1d ago
Your first thought is correct. However, microwaves do not heat up things by.... sending microwaves? They rotate the water molecules! So, since the ceramic of mug absorbed water molecules, when u microwave it those water molecules will rotate and heat causing the mug to become hotter than before.
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u/ArrowDel 1d ago
If mug is extra hot after microwaving and you used this mug this way before, I would presume the internal enamel is cracked enough the ceramic is getting wey
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u/originalnamesarehard Chemistry 1d ago
meecrowavey makes things hot!
don't put it in microwave, it won't get hot as often!
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u/AbbreviationsNo8702 1d ago
Thanks, i have a chiped mug here and now I understood why the cracks are growing, gonna dispose of too
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u/PrudentCompany9828 1d ago
Maybe a wild far out thought, but could it be due to the same idea of using a spoon that has no points to heat a cup of water more efficiently? Those jagged edges from the break could be doing the same thing on why you can't use a fork vs a round handled spoon in a cup of water.
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u/FPS_Warex 1d ago
Could probably seal it up with some nail polish? No clue weather it's safe for microwaves, but would assume so🤷♂️
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u/thatthatguy 23h ago
Mug is not microwave safe. Porous ceramic could break unexpectedly. Do not microwave.
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u/kazumarukuwabara 1d ago
Removed the glaze coating and the microwaves can hit the interior of the mug then heat spreads through the inside.
I dont know what I talking about but it sounds like it could be right.
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u/glxykng 1d ago
Your first thought is 100% correct. Water is absorbing through the porous area and is heating up.