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too-hot dishes in microwave

Posted by mandogirl (My Page) on
Tue, Jun 3, 08 at 10:54

Hi! I didn't want to hijack Annie's birthday food thread, but she said something I wanted to ask about. She said that plates that get too hot in the microwave (hotter than her other newer dishes) might contain higher levels of lead. Does anyone know if there is any truth to this or if this should be a concern?

I ask because my favorite coffee mug is from when I was a kid in the mid-1970's. It's cream colored and has my name printed in diagonal capital letters in brown. (These were popular then, I think. I can't believe mine still survives. I love it because it's the perfect size.) Anyway, I can't microwave this mug because it gets just too dangerously hot...especially the handle. Much hotter than any of my 1999 Pfalzgraff dishes. I'm curious now after Annie's thread about whether I should really be drinking from this mug as often as I do!

Anyone know about lead in old ceramics?


Follow-Up Postings:

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RE: too-hot dishes in microwave

Properly fired pottery, even if it does have lead in the body of the ware is save. It's the cheap, low fired stuff that chips easily that is dangerous.
Lots of clay has feldspar in it which will absorb microwave energy as do fats and sugars. That means the energy is going into the pot not into heating the food.
Your cup won't hurt you unless you bought it in Nogales on the street.
Lots of old stoneware, old ironstone gets hot in the microwave, but is very safe to use.
Linda C


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RE: too-hot dishes in microwave

Dishes that are hot in th3e microwave don't necessarily have lead in them. You can only tell by testing, and can buy a lead testing kit at your local hardware store or online for $10 or less.

Whether or not your dishes get hot in the microwave can also depend on the porous nature of the item, things like stoneware get hotter, especially in you're heating something without liquid or the glaze is "compromised". The item could be made out of some other metallic elements, or the glaze could. The only way to really know is that test kit.

This came from one of those "informational" websites, Uclue.

"Materials with a high moisture and/or fat content such as food or are examples of materials that absorb microwave energy. The microwaves enter the food and agitate, or "excite" the atoms, which makes them hot.

"Microwave transparent" materials such as glass, paper, parchment, and most pottery and plastics are examples of materials that allow microwaves to pass through.

Metals, on the other hand, reflect the energy, which is why users are cautioned not to use metal dishes in a microwave. The waves simply bounce off the metal instead of going through or being absorbed by it.

So you can see then that certain mugs or dishes that get hot in a microwave might be made of a material that absorbs the waves to some degree. Stoneware is one, especially if there are an chips or cracks in it
that might allow moisture to creep in. The water will then absorb the microwaves and allow the cup or dish to become very hot. Lead crystal might also absorb the waves to some extent, as well as some ceramics."

Another researcher stated:

"The high porosity of earthenware makes it necessary for manufacturers to glaze them and this glaze frequently has lead. If not treated at a high temperature during the glazing process, the leaden glaze will leach over the life of the product..

Which is why I stop family members from microwaving mugs of java or any liquid unless I'm sure that they were not made in countries where toxicity is not a concern! In fact, I'm never sure as I don't know about the toxicity tests required by importing states or countries."

Some things naturally contain lead, like lead crystal. We are urged not to use them daily or store food in them. And of course, my beautifully spring green plates were very cheap and made....um, yeah....in China, a country which has lately gotten some very bad press about lead paint in dishes, children's toys, cheap furniture, etc.

So, Elery bought me new ones, along with a lead testing kit. We tested the new dishes, but haven't yet tested the old ones.

Annie


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RE: too-hot dishes in microwave

The lead question aside, the test for whether a container is safe for the microwave is whether or not it gets hot when used there. Your cup SHOULD NOT be used in the microwave if it's getting that hot. The food should get hot, the container should only get a little warm, due to heat transfer, but a truly hot container should be used for other purposes, not in the microwave.


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RE: too-hot dishes in microwave......

Stoneware or whatever that gets hot in the microwave is not unsafe to use, but for the fact that it will absorb the waves rather than the food and you may not get something cooked enough if you are going by the clock.
Something that gets hot in the microwave won't necessarily poision you, but if you are using it for something that takes a long time to cook, you may harm the dish.

The issue of using dishes made in other countries is "supposed" to be controlled. Partly by the McKinley Tarrif act that states that products for import into this country must be labeled permenantly with the country of origin, and partly by the fact that our government inspects all ware to be sold here and those that may contain harmful metals MUST(they say) be permenantly labeled "not for food" or have a hole in it ( as a flower pot).
So....as I said, unless you bought it on the street in Nogales of brought it back form a little shop in Spain, it's safe.
All my imported dishes are made in France or England...or Japan, and they are not pottery/ceramic.
There is porcelain like "fine china" or Mikasa's "Everyday china" which is high fired and never any danger because of the temperature at which it must be fired.

And there is stoneware, which is a high fired ware as well, the body of the piece actually melts together...vitrifies, and that is no harm. Then there is ceramic or pottery which takes a lower temperature for firing and is there by cheaper and is often covered with brightly colored glazes which may contain harmful metals. Think old majolica, bright Mexican or Spanish pottery. But that can't legally be imported for resale....so the main source is someone bringing it into this country as a souviniere.

If you use your head, and don't eat from something not made for food you are more likely to get lead in your system from the old paint on an old house than from your coffee cup.

Here is a link that might be useful: Cooking for engineers


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RE: too-hot dishes in microwave

Thanks for all the info! You can bet I only tried microwaving my circa-1970's name mug once! Never again. I'll happily continue drinking from it, though. ;-)
It was probably made in China, as I'm sure these were mass-produced. Mine was my hot chocolate mug as a kid; Mom would make Hershey's cocoa with big marshmellows floating in it on snow days when school was canceled. Now 30-some years later it's my coffee mug. ;-)


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RE: too-hot dishes in microwave

Nope, sorry LindaC. All items are supposed to be labeled with the country of origin and are supposed to meet standards but the government says they only have money and workers enough to inspect 2 or 3 percent of the stuff that comes in. That's how all those Mattel toys (including Dora the Explorer, Big Bird, Elmo and Thomas the Train) got recalled for lead paint from China, that's how we got the contaminated pet food from China that killed all those pets and that's how we got the tainted toothpaste from China with the poisonous chemicals. In addition, dishes that are safe today, or were safe 10 years ago might not be safe today, as acidic foods can compromise the glazing and allow the lead to leach into your food. So can cracks, chips and repeated trips through the dishwasher.

Most stoneware is perfectly safe, especially those who don't have a painted on pattern such as a gold edge or a floral border, etc. Many times the dish itself is properly glazed and fired, then painted afterward so the pattern is the culprit, no matter whether it came from Nogales or Shanghai.

Nope, our government is not above to protect us, and says so. We've got to watch these things for ourselves and use common sense.

Annie


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RE: too-hot dishes in microwave

Note my caveat:

"The issue of using dishes made in other countries is "supposed" to be controlled. Partly by the McKinley Tarrif act that states that products for import into this country must be labeled permenantly with the country of origin, and partly by the fact that our government inspects all ware to be sold here and those that may contain harmful metals MUST(they say) be permenantly labeled "not for food" or have a hole in it"

If a dish has a painted on pattern after glazing, you certainly don't want to be putting it into the microwave, not because it might be unsafe but because you will surely ruin the dish.
Dishes with a gold edge cause a very interesting "display" when put into the micro! You are not likely to do it often, unless you are a slow learner!
I am very curious what you find in your dishes with the lead testing kit....and what you find on your walls and around the house in places where solder may have been used.

I shudder when I remember that my son had a kit for making toy soldiers out of lead. He collected used lead tire weights and fish line weights, melted them down over an alcohol burner in the basement and poured the molten lead into a mold!...AARGH....but we didn't know then! Lead gasses and he was in a closed little room in the basement...
But when I was little, we had leaded gasoline.
Perhaps that's why I am cavalier about testing my dishes for lead.
Linda C


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RE: too-hot dishes in microwave

The part I was disagreeing with was the part where you said they MUST inspect. There is no MUST inspect, they inspect randomly, about 2 shipments out of every hundred. It's very easy for stuff to "slip though".

Yeah, I grew up with unleaded gas too, and I rode all the way to Canada once in the bed of a pickup truck with a camper/topper on it. Understand, I'd never let my kids do that, but I did it. LOL It's a miracle any of us survived, maybe it was one of those survival of the fittest things? (grin) Of course, the tobacco companies also used to promote cigarettes as a health BENEFIT, so times have changed slightly...

At any rate, I've gotten dumber as the years go on, from the time when I was a teenager and knew everything. I've discovered that I know less and less each year and so much do what I can to protect the few precious brain cells I have left.
Annie


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RE: too-hot dishes in microwave

This is a very informative thread. It has convinced me to look for a new set of pottery dishes that is made in the USA and labeled safe for the microwave and the dishwasher.


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RE: too-hot dishes in microwave

Having taken pottery classes for several years, including an excellent course in clay and glazes, I can offer a few comments about pottery, helpful ones I hope.

The problem of too hot ceramic dishes from the microwave is due to metal molecules in the glazes and sometimes in the clay. Clays are composed mainly of the mineral feldspar and so are glazes. Pure clay will not be appreciably heated by microwaves. But glazes contain metal compounds to make them melt, become glassy, and flow at temperatures lower than the melting point of the clay itself. Metal compounds are also used to create colors in glazes. The metals used in glazes are lead, iron, cobalt, copper and many others. These metals will be heated by microwaves, just as a metal baking pan will be. No mystery about that. Well, OK, the amount of metal in a pottery bowl is much less than in a metal baking pan, but it works exactly the same way, just to a lesser degree. And not just with lead glazes.

A clay may contain metal compounds to varying degrees too, usually iron. A white clay such as porcelain contains little or no iron. Gray clays, such as stoneware or earthenware clays which become red, brown or black when fired contain significant amounts of iron, which is a common element.

Comparing a bowl I made of stoneware, which I glazed with a dark brown, iron-rich glaze to a bowl I made of porcelain and glazed with a pale green, transparent, glaze (celedon which gets its color from a minimal amount of iron), they react quite differently in the microwave. The brown one gets hot -- usable, but pretty hot. The celedon bowl doesn't heat up noticeably.

BTW, I hope everyone remembers what Linda said about gold decorated china. It could easily be overlooked. That decoration is real, metallic gold and will react to microwaves as you should expect.

Safe glazes can be made with lead, which is a useful flux. If a glaze is properly formulated, and it's easy to do, the lead will be bound chemically, not just physically, and will not leach out, even with chips and cracks. But, since this is a fine point of glaze chemistry which is lost on most consumers, potters and manufacturers these days just avoid the problem by not using lead and truthfully marking their wares "lead-free".

Pottery made in Mexico and other countries is a different story. Lead is still used and not always in a safe way. I practically tripped over a big bag of lead oxide while visiting a Mexican pottery studio and some of the pottery I brought back tested positive for lead using one of those hardware store kits. I like the pottery but I don't eat out of it. I think one should be cautious about some of that beautiful Italian pottery too, even though we don't think of Italy as third world.

Well, there are lots of exceptions and other details to this subject, but that's the gist of it as best I can tell.

Jim


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RE: too-hot dishes in microwave

One metal used in glazes which I had forgotten about until Sue started a thread about Fiestaware is uranium. If you like lead in your glazes, you'll love uranium. :-)

Actually, I can't tell you whether or not to worry about red or cream colored older Fiestaware. The red especially has a significant uranium content. These glazes definitely give off radiation, but I don't know if the levels of exposure are something to be concerned about. You decide.

Jim

Here is a link that might be useful: Fiestaware Uranium Glazes


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RE: too-hot dishes in microwave

years ago, a noted potter was commissioned to make a yellow platter for presentation to Queen Elizabeth. It was radioactive!
Another danger I haven't seen mentioned is crazing -- a lot of fine lines (actually cracks) throughout the piece, particularly in the bottoms of the vessel. Crazing occurs with age and will be seen in many older pieces. It also occurs on new pieces when there isn't a proper fit between the clay base and the glaze.
Some potters feel washing in the dishwasher makes crazed pieces okay to use -- I personally do not think dishwasher temps make a crazed piece safe.


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RE: too-hot dishes in microwave

Many glazes are supposed to craze and crackle. It is part of the beauty of those particular glazes and it is often an on going process. I don'y think there is any problem with that. Copper and cobalt are great conductors and glazes with a lot of either can be uncomfortabley warm when heated in the microwave but I don't think they present any danger. Lead vaporizes at a relatively low tempeture and would not be used in stoneware. In low fire ware it is a different story. If it has been improperly or unevenly fired the lead is seriously risky. If you have already done it enough you will be too dumb to care so don't worry.

Many yellow glazes contain rare and exototic metal but I think that that particular potter would know how to use them safely and unless he had a hidden agenda the queen would have been safe.

Linda reminded me that my brother and cousins and I used to make lead soldiers all the time. I don;t remeber being told not to but we must have thought so because we always did it when and where there were no adults around. So if I seem a little loopy try to be kind.


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RE: too-hot dishes in microwave

Yes, many glazes are designed to craze -- in our studio usage of such glazes was recommened "for decorative use only" --
I mentioned crazing not because of possible leaching of lead or other oxides, but because the little critters that take up residence in the cracks -- you know bacteria such as e coli, etc.


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RE: too-hot dishes in microwave

Something puzzles me. Many of out forum members consider farm raised salmon a health risk, yet nobody has expressed a single concern about the safety of radioactive dinnerware.

Jim


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RE: too-hot dishes in microwave

Jim, there's not a lot of radioactive dinnerware....well maybe the old orange Fiesta....and probably that wonderful old green/yellow glass variously known as vasoline glass or uranium glass...
But I keep mine in the top cupboard...:-Q
Again....the problem with pottery that gets hot in the microwave is not that it emits unsafe "stuff" but that it absorbs the micro waves that should be used to cook the food.
And....microwaves are not absorbed by metals but reflected.
Linda C


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RE: too-hot dishes in microwave

"Jim, there's not a lot of radioactive dinnerware....well maybe the old orange Fiesta...."

That's what I'm talking about, Fiesta red. It's loaded with uranium. It's radioactive. Nobody cares?

"...it absorbs the micro waves..."

"...microwaves are not absorbed by metals..."

There is a contradiction here.

Jim, who is off to the supermarket to buy some delicious, healthful, non-radioactive, farm-raised salmon for tomorrow's meal.


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RE: too-hot dishes in microwave

...off to the supermarket to buy some delicious, healthful, non-radioactive, farm-raised salmon for tomorrow's meal.

And packed with mouth watering pesticides.


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RE: too-hot dishes in microwave

I've used a same mug for a long time to warm up milk in the micro. It never got so hot to handle. But recently Ive noticed it's getting VERY hot and need a potholder to take out and cannot even use to drink from it cuz I'll burn my lips as well. I'm using same temperature. What could explain the change?


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RE: too-hot dishes in microwave

To ily, I saw this exact problem described in another forum, and this is what I posted:

Maybe NOT so wierd - that is the exact reason I ended up googling about ceramics in the microwave! Many dishes are fine for years and years, and then they become blisteringly hot, and they never seem to get better. Some handmade, some made in France, some misc... Curious!

Reading a few forums, I am wondering if it is multiple dishwasher passes, and maybe normal micro-cracks, over time, allowing sugars or fats to seep in, allowing superheating?

Gaaaaa.....!


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