# Microwave safe dishes ??? **URL:** \ **Category:** Factual Questions\ **Created:** [January 1, 2004, 8:15pm UTC](https://boards.straightdope.com/t/microwave-safe-dishes/222156 "2004-01-01T20:15:32Z")\ **Posts on this page:** 15\ **Page:** 1
**Author:** ![simple\_homer](https://avatars.discourse-cdn.com/v4/letter/s/9de0a6/32.png) [@simple\_homer](https://boards.straightdope.com/u/simple_homer)\ **Post date:** [January 1, 2004, 8:15pm UTC](https://boards.straightdope.com/t/microwave-safe-dishes/222156/1 "2004-01-01T20:15:32Z")
I live in the Philippines, and it is very hard to find dishes that are marked microwave safe. Are there any ways of telling if a dish is safe or not ? And, what makes a dish not safe ?? And what is the harm in using it, does it damage the food or the dish ? Sorry if this has been asked before, but I could not find this when I did a search. ---
**Author:** ![robcaro](https://avatars.discourse-cdn.com/v4/letter/r/df705f/32.png) [@robcaro](https://boards.straightdope.com/u/robcaro)\ **Post date:** [January 1, 2004, 8:54pm UTC](https://boards.straightdope.com/t/microwave-safe-dishes/222156/2 "2004-01-01T20:54:21Z")
Internet has this to say about it: [http://housewares.aubuchonhardware.com/buyers\_guides/all\_about\_microwave\_cookware.asp](http://housewares.aubuchonhardware.com/buyers_guides/all_about_microwave_cookware.asp) > [@](#): > > Microwave cooking requires the use of microwave-safe cookware. Some kinds of cookware can become very hot in the microwave and pose a hazard. Generally, microwave-safe cookware does not heat up in the microwave as the cooking energy is absorbed by the food… > > A simple test to determine if a dish is microwave-safe is to place the dish in question in the microwave along with a cup of cold water in a known microwave-safe item. Microwave on high (100 percent) power for one minute. If the water has heated and the dish has remained cool, it’s microwave safe. If the dish tested has gotten warm or hot, it should not be used in the microwave oven. ---
**Author:** ![simple\_homer](https://avatars.discourse-cdn.com/v4/letter/s/9de0a6/32.png) [@simple\_homer](https://boards.straightdope.com/u/simple_homer)\ **Post date:** [January 2, 2004, 3:30am UTC](https://boards.straightdope.com/t/microwave-safe-dishes/222156/3 "2004-01-02T03:30:30Z")
Thanks Robcaro, but does anyone know what makes some dishes unsafe? Does the dish become too hot and possibly explode ? Or does the dish poison the food ? What is it that makes some dishes not safe ? Thanks ! ---
**Author:** ![quelquechose](https://avatars.discourse-cdn.com/v4/letter/q/6f9a4e/32.png) [@quelquechose](https://boards.straightdope.com/u/quelquechose)\ **Post date:** [January 2, 2004, 4:03am UTC](https://boards.straightdope.com/t/microwave-safe-dishes/222156/4 "2004-01-02T04:03:31Z")
I believe that a non-microwave safe dish heats up. I once put a dish in a microwave, which looked slightly orange after awhile. I didn’t know why, so I left it in. When I took it out with an oven glove, it was so hot that the glove burned. I stuck the dish in the sink, where it subsequently exploded, in a bizarre, perfectly symmetrical way, leaving a small circle of what used to be a dish intact. It was quite exciting. ---
**Author:** ![vandal](https://avatars.discourse-cdn.com/v4/letter/v/858c86/32.png) [@vandal](https://boards.straightdope.com/u/vandal)\ **Post date:** [January 2, 2004, 4:28am UTC](https://boards.straightdope.com/t/microwave-safe-dishes/222156/5 "2004-01-02T04:28:04Z")
Well, the theory goes that microwaving foods in ordinary plastic dishes causes harmful carcinogens from the plastic to enter the food. There are some manufacturers of plastic dishes which claim that their plastic is microwave safe, not only from melting, but from the release of these carcinogens. [Snopes](http://www.snopes.com/toxins/plastic.htm) has something say about it. ---
**Author:** ![Ms2001](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ms2001/32/18463_2.png) [@Ms2001](https://boards.straightdope.com/u/Ms2001)\ **Post date:** [January 2, 2004, 6:45am UTC](https://boards.straightdope.com/t/microwave-safe-dishes/222156/6 "2004-01-02T06:45:42Z")
> [@](#): > > \*Originally posted by simple homer \* > **Thanks Robcaro, but does anyone know what makes some dishes unsafe?** I have some matching mugs, plates, and bowls that heat up in the microwave. I suspect it’s something in the paint; the microwave safe dishes are plain blue and white, but these are decorated with red, green, and blue patterns. They don’t get hot enough that I might get burned or that they might explode, but I avoid using them because the food doesn’t get cooked very well. ---
**Author:** ![engineer\_comp\_geek](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/engineer_comp_geek/32/504_2.png) [@engineer\_comp\_geek](https://boards.straightdope.com/u/engineer_comp_geek)\ **Post date:** [January 2, 2004, 7:10am UTC](https://boards.straightdope.com/t/microwave-safe-dishes/222156/7 "2004-01-02T07:10:14Z")
Some dishes have metallic paint, or will have a metallic ring around the outer edge somewhere for decorative purposes. These can get very hot in a microwave, due to eddy currents being induced into the metal, and the plate can get very hot or can even crack under the thermal stresses. Another example of a non-microwave safe plate would be a plastic one with a relatively low melting temperature. If you heat up something hot, the plate will melt. These types of plates and glasses can also turn into goo in a hot dishwasher. I personally haven’t seen anything conclusive about plastics releasing poisonous materials, but that is a theory about certain types of plastics. The snopes article referenced in one of the previous posts seems to cover the issue fairly well. ---
**Author:** ![Extraneous](https://avatars.discourse-cdn.com/v4/letter/e/0ea827/32.png) [@Extraneous](https://boards.straightdope.com/u/Extraneous)\ **Post date:** [January 2, 2004, 11:13am UTC](https://boards.straightdope.com/t/microwave-safe-dishes/222156/8 "2004-01-02T11:13:32Z")
Microwaves heat WATER. Period! If an item contains no water, it will not be heated by a microwave. Some plastics use water to provide pliablility - these will melt in a microwave. Ceramic, stoneware, glass, et. al. are good candidates for microwave use - as stated above, nuke your test object for a minute (or 3) on high - if it remains cool, it is (probably) safe. If it heats up, do not use it for microwaving. p.s. - now you know why the instructions tell you to “let stand in microwave x minutes after cooking” - various foods have varying water content - the “wet” ones get hot, while the “dry” ones remain cool. The waiting period allows for radiation heating - the hot items heat the air, which heats the cooler items. The idea is to allow a thermal equilibrium to be reached prior to serving. ---
**Author:** ![engineer\_comp\_geek](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/engineer_comp_geek/32/504_2.png) [@engineer\_comp\_geek](https://boards.straightdope.com/u/engineer_comp_geek)\ **Post date:** [January 2, 2004, 12:05pm UTC](https://boards.straightdope.com/t/microwave-safe-dishes/222156/9 "2004-01-02T12:05:18Z")
> [@](#): > > \*Originally posted by Extraneous \* > \*\* > If an item contains no water, it will not be heated by a microwave. > \*\* If there is metal present in a microwave, currents are going to be induced in it by the radio waves. These currents are going to circulate around through the metal. Since the metals aren’t superconductors, there is some resistance to the currents moving around, which means that heat is generated. Thinner metals get hotter, since the resistance is greater. This is how those little metal foil/cardboard things work inside microwave lunches. The metal foil gets hot, which heats up the crust of your mini-pizza or hot-pocket or whatever. This is necessary for foods like pizza crust which won’t cook properly by themselves in a microwave. They need plain old fashioned heat. ---
**Author:** ![swansont](https://avatars.discourse-cdn.com/v4/letter/s/5fc32e/32.png) [@swansont](https://boards.straightdope.com/u/swansont)\ **Post date:** [January 2, 2004, 12:09pm UTC](https://boards.straightdope.com/t/microwave-safe-dishes/222156/10 "2004-01-02T12:09:11Z")
> [@](#): > > \*Originally posted by Extraneous \* > Microwaves heat WATER. Period! > > If an item contains no water, it will not be heated by a microwave. No, microwaves operate at a frequency that is readily absorbed by water. There is no reason that some other material can’t absorb that frequency. > [@](#): > > p.s. - now you know why the instructions tell you to “let stand in microwave x minutes after cooking” - various foods have varying water content - the “wet” ones get hot, while the “dry” ones remain cool. The waiting period allows for radiation heating - the hot items heat the air, which heats the cooler items. The idea is to allow a thermal equilibrium to be reached prior to serving. There is uneven heating in microwaves - the wavelength is a few cm long, so there may be nodes if there is no stirrer or the plate doesn’t rotate, so you get cold spots and hot spots. Equilibration is happening, but not with the mechanism (it’s conduction within the food) or reason you state. ---
**Author:** ![simple\_homer](https://avatars.discourse-cdn.com/v4/letter/s/9de0a6/32.png) [@simple\_homer](https://boards.straightdope.com/u/simple_homer)\ **Post date:** [January 2, 2004, 12:29pm UTC](https://boards.straightdope.com/t/microwave-safe-dishes/222156/11 "2004-01-02T12:29:59Z")
Extraneous “Ceramic, stoneware, glass, et. al. are good candidates for microwave use - as stated above, nuke your test object for a minute (or 3) on high - if it remains cool, it is (probably) safe. If it heats up, do not use it for microwaving.” Ok, but WHY would ceramic, stoneware, or glass heat up in the microwave, and WHY would it not be safe to use just because it is hot ??? Thanks for all the replies, but I still don’t have an answer to my question, I understand about plastic melting, but not about the others. Thanks again ---
**Author:** ![engineer\_comp\_geek](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/engineer_comp_geek/32/504_2.png) [@engineer\_comp\_geek](https://boards.straightdope.com/u/engineer_comp_geek)\ **Post date:** [January 2, 2004, 12:43pm UTC](https://boards.straightdope.com/t/microwave-safe-dishes/222156/12 "2004-01-02T12:43:50Z")
> [@](#): > > \*Originally posted by simple homer \* > \*\* > Ok, but WHY would ceramic, stoneware, or glass heat up in the microwave, and WHY would it not be safe to use just because it is hot ??? > \*\* A few things come to mind. 1. Because it heats up unevenly, which could cause it to shatter from the mechanical stresses of uneven expansion. 2. Because you can burn the \*\*\*\* out of your fingers taking it out of the microwave 3. Not really a safety thing, but if it’s absorbing the microwaves then your food isn’t. It will take longer cooking times to make your food hot. ---
**Author:** ![engineer\_comp\_geek](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/engineer_comp_geek/32/504_2.png) [@engineer\_comp\_geek](https://boards.straightdope.com/u/engineer_comp_geek)\ **Post date:** [January 2, 2004, 12:47pm UTC](https://boards.straightdope.com/t/microwave-safe-dishes/222156/13 "2004-01-02T12:47:09Z")
Should have thought a bit longer. 1. Things like cups with metal rings can actually be damaged by the microwave. 2. Anything metallic can theoretically end up reflecting microwaves back into the magnetron, damaging your microwave oven Swansont answered why other materials heat up. Water isn’t the only thing that absorbs microwaves. ---
**Author:** ![netscape\_6](https://avatars.discourse-cdn.com/v4/letter/n/8c91f0/32.png) [@netscape\_6](https://boards.straightdope.com/u/netscape_6)\ **Post date:** [January 2, 2004, 1:04pm UTC](https://boards.straightdope.com/t/microwave-safe-dishes/222156/14 "2004-01-02T13:04:18Z")
I used to a cup that had metalic paint, it turned out it had actual metal in the paint. Talk about a light show. The lines that were burnedin the paint were interesting too. ---
**Author:** ![Cillasi](https://avatars.discourse-cdn.com/v4/letter/c/71e660/32.png) [@Cillasi](https://boards.straightdope.com/u/Cillasi)\ **Post date:** [January 2, 2004, 2:02pm UTC](https://boards.straightdope.com/t/microwave-safe-dishes/222156/15 "2004-01-02T14:02:52Z")
In general, some plastics and most metals are not micro-wave safe. Some plastics may release questionable substances when exposed to microwaves. Metals can spark and smoke and will actually produce an ashy substance (i.e., individual butter servings in those little foil sealed tubs). Some ceramic and stoneware may be decorated or coated with polymer materials that can also release substances when heated. Here is a site that details some of the supposed dangers of using non-microwave safe items. > **[Urban Legends Store](https://shop.urbanlegends.com)** > > Shop exclusive music from the Official Urban Legends Store. It also has a series of links to other sites that examine this question.