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stoneware bowl gets very hot in microwave

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I have 4 bowls that I am sure are stoneware (safe in micro?). But they get extremely hot in the micro. They are colored red. Would that have any effect? Someone said that the paint might have lead. Would lead being in the paint affect me? And how can I find out if there is lead in the paint?

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  1. If you put some water in a bowl and put it in the microwave, the water should come out hot not the bowl. As to testing for lead, there are kits you can buy at many hardware stores.

    1. In another thread the OP talked about warming her plates in the microwave. After extensive discussion we learned that they were stoneware (or something like that). It sounded as though her stoneware reacted to the waves less than melamine, but more so than glass (or Corellware) - enough to warm up but not so much as to be dangerous.

      I don't recall anyone suggesting why stoneware was reacting.

      1. I have stoneware too, it gets hot in the microwave also. My other plates do not.

        1. http://ceramicstoday.com/articles/031...
          says that while metal in the glaze might produce arching, moisture in the ceramic might produce steam. I had a earthenware bowl get hot in a microwave because it was only glazed on the inside, and I had soaked it in water as per manufacturer's instructions.

          1. The bowl is going to heat up because whats in the bowl heats up.

            8 Replies
            1. re: Dave5440

              Yes, pretty much the case. The food heats up and yes, it will transfer to the vessel just like anything else you heat up. Put hot soup in a bowl and the bowl will get hot. I don't seem to find much difference between stoneware, china, and French porcelain - they all get hot to varying degrees.

              1. re: breadchick

                Though a reasonably observant individual should be able to distinguish between heat that is generated in the bowl itself from that conducted from the food. The fact that OP is commenting about the bowl getting hot, suggests that he has noted the difference. I mentioned another thread where the poster was warming bare stoneware plates in the microwave.

                1. re: paulj

                  how one one distinguish between the 2 , bowl hot contents hot,

                  1. re: Dave5440

                    The rim of a bowl should not get hotter than the contents.

                    1. re: paulj

                      The sharpest edge should get the hottest, which is the rim

                      1. re: paulj

                        Silly. If you stick plastic wrap over the bowl, the rim will certainly get hot. Anyone that spends major time at the office micro knows this. The poster didn't distinguish between vessel and contents. The issue is the red coating and if it's the source of the problem. (Perhaps the country of origin may be an clue.)

                      2. re: Dave5440

                        a Pyrex measuring cup is a classic example -- you can actually boil water in a Pyrex vessel in the microwave, but the handle will stay cool (as will the rim of the measuring cup...at least for a few minutes until the heat transfer warms it all up)

                        1. re: Dave5440

                          If i defrost something on my one set of stoneware plates, the plate gets very hot, while the food just gets defrosted.

                  2. I have found that most all stoneware gets hot in the microwave - that is, the stoneware itself gets hotter than the contents if left in the microwave long enough. I have also found that some stoneware repeatedly microwaved will show crazing in the glaze.

                    The simple answer is just to use porcelain - it just works much better in the microwave, and it can be put in the oven as well. You have to do some studying to learn to tell the difference, as pieces aren't always marked clearly if they are stoneware or porcelain. Personally, I don't buy any stoneware at all for just this reason.

                    Porcelain is fired at higher temps than stoneware, and is fully vitrified. It generally isn't any more expensive than stoneware, but typically it is white colored only - I don't see many colorful porcelain pieces.

                    4 Replies
                    1. re: pweller

                      Your answer is interesting to me as I am looking at these cups
                      for purchase.
                      Reading the information about these cups, it mentions that

                      "Rich blue chinese inspired pattern created with hand applied lithographs underglaze for vibrant color and durabilty on a porcelain white body"
                      "Never place empty items in microwave or oven."

                      So I assume the reason in this case for not placing the cup in the microwave is probably due to the glaze.

                      But I am not sure. Any thoughts about this? Thanks.

                      1. re: Rella

                        I can't really give you a definitive answer - I'm not an expert, I just know what I've learned by trial and error. I have found some people use the term porcelain as sort of a catch-all phrase. I know if you fire real porcelain, that it generally comes out pure white. Now, if you want that same color on stoneware, you can just glaze it white first. So, my question on your mugs, is it really porcelain or is it stoneware with a white glaze?

                        One tip-off is to look at the foot of the piece (that is, the unglazed rim at the bottom of the piece). Porcelain will be pure white, and will be fairly smooth. Stoneware is typically beige, or some other color, and isn't nearly as smooth. You can study whatever pieces you have laying around and see what you can learn. Generally, porcelain feels heavier/denser to me than stoneware.

                        From what I've read, stoneware can absorb moisture through the foot, and it is this moisture that causes the pieces to heat up. Porcelain is fully-vitrified, so it is basically the same from the surface to the inside, and doesn't absorb moisure.

                        The phrase 'never place empty items in microwave or oven' puzzles me. I don't know why it would matter.

                        For some reference, I bought a few things from here, and they do describe the items as 'fully vitrified' and indeed they are: http://www.bryanchina.com/white_china...

                        I think the main problem is that many people don't know the difference, and the descriptions can be misleading.

                        Here's one decent article describing the differences. http://www.bestofthehome.com/metal/ce...

                        So, I just learned something new myself. I saw a number of references to porcelain being translucent, but I thought my everyday tableware was too thick to transmit light. However, I put a powerful, modern LED flashlight on the back of my plate, and could faintly see light through it. That seems to be a valid test, but you need a bright light for thicker pieces.

                        1. re: pweller

                          What a wonderful answer -- got my flashlight out! I have count-on-one-hand porcelain items, but I do have a similar cup with no markings on the bottom It is a very old piece, and it no doubt is porcelain.
                          I was looking at a baking tart pan at TJMax the other day, white, but the bottom was a definite almost-darkish beige.
                          I did buy 4 tart Pillivyut 5-1/4 porcelain from Amazon, and they pass the white on bottom test.
                          Thanks again for your valuable reply.

                          1. re: Rella

                            I don't think the 'white on bottom' observation is conclusive, because I have some earthenware/stoneware that looks pretty white (though if I compare it side-by-side with known porcelain, I can see a difference). Obviously, if the color of the clay is beige, then you know it isn't porcelain,

                            The flashlight test is conclusive for porcelain, because neither stoneware nor earthenware transmit light. That being said, I don't know if there is such a thing as 'white glass' tableware that could look like porcelain and transmit light. I have seen some really thin translucent plates at Wal-Mart, and I'm not sure what they are made of - they might be marked but I've never checked.

                    2. If you fill the bowl about a quarter full of water and heat for a bit, the water should be warm the bowl basically cool. If the bowl if as hot or hotter than the water than my understanding is you have a bowl that is not microwave safe.

                      3 Replies
                      1. re: escondido123

                        Even a glass measuring cup can get hot in the microwave. The handle will nt but the transferrence of heat from the water to the sides of the cup cannot be avoided.

                        1. re: Candy

                          I just went to check on this and find out there is a US Food Safety method for testing. Here it is:
                          "Put one cup of tap water in a glass measure. Place the water in the microwave oven along with (but not touching) the utensil to be tested. Microwave on high 1 minute. If the utensil feels warm or hot, it is not microwave safe because it contains metal in the material or glaze. Do not use it. The utensil and/or the bottom of the oven might crack if microwaved.".

                          1. re: escondido123

                            The idea of the extra cup of water is that some microwaves warn against use when empty - empty meaning no object that can absorb the waves. This test gets around the problem of the contents warming the container.

                      2. I'm not quite sure about this, but I believe the red color in some stoneware/earthenware/ceramics has been connected to cadmium, which is toxic.
                        I don't know if there are kits testing for cadmium, though.

                        1. Stoneware is not porcelain. Porcelain and bone china are close cousins. Bone china, the whitest and most durable, suprisingly, is bone china. They are both produced from hard paste clay and bone china has had bone (animal) ash added to the clay for durability and the pure white color. Porcelain when compared side by side to bone china will look slightly grey unless it has been glazed to appear pure white. Fine china also falls into this group thing Lenox. It is glazed to a creamy color.

                          True stoneware is made from a different clay and is of course, thicker and heavier. It is fired at very high temps. and most often becomes vitrified. Think of Dansk for example. Ironstone is at the bottom of the pile. It is not often made any longer. The clay used to produce it is very soft it chips and cracks easily. The name was given to imply strength and durability.

                          Now, about heating in the microwave. Red glazes contain metal. Long ago it may have been lead and if it has been produced in Asia it may still be. Red glass is more expensive because it requires gold to achieve a rich color. The metal can vary depending on the color depth that is trying to be achieved. You can count on red colored pieces to heat up because of the glaze. I have some Waechtersbach stoneware in solid red made in Germany. It always gets hot in the microwave and I also have a number of coffee mugs made by them too, not red, and they are fine in the microwave.

                          To not go on too long, yes almost every thing you pot in the microwave will eventually absorb heat. It is the convection factor IE food etc. gets hot and transfers to the vessel. That is why a cup or mug may get hot but the handles will remain cool. Another caveat, never put gold or platinum trimmed dinnerware in the 'wave. The trim will cause arcing and it will also tarnish the trim and blacken it.

                          2 Replies
                          1. re: Candy

                            My stoneware plates get hot in the dishwasher! why is this?

                            1. re: Dave5440

                              The heat of the water in the dishwasher is very hot. If you use the heated dry setting that will further add heat to help the water evaporate.