# Aluminum in post 1980 microwaves **URL:** \ **Category:** Factual Questions\ **Created:** [September 28, 2020, 6:34pm UTC](https://boards.straightdope.com/t/aluminum-in-post-1980-microwaves/921757 "2020-09-28T18:34:15Z")\ **Posts on this page:** 10\ **Page:** 2
**Author:** ![squeegee](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/squeegee/32/14537_2.png) [@squeegee](https://boards.straightdope.com/u/squeegee)\ **Post date:** [September 29, 2020, 12:31am UTC](https://boards.straightdope.com/t/aluminum-in-post-1980-microwaves/921757/21 "2020-09-29T00:31:41Z")
> [@wolfpup](#): > > like the fact that all or most of the bottom of the aluminum tray should be covered with the food, so microwaving a half-used portion could be bad news The picture I posted in the OP was the result of nuking a half used portion. Worked fine, microwave didn’t open any wormholes or nothing. ---
**Author:** ![squeegee](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/squeegee/32/14537_2.png) [@squeegee](https://boards.straightdope.com/u/squeegee)\ **Post date:** [September 29, 2020, 12:33am UTC](https://boards.straightdope.com/t/aluminum-in-post-1980-microwaves/921757/22 "2020-09-29T00:33:39Z")
> [@Vesicant](#): > > The 1980 changes may be the result of the 1975 Energy Policy and Conservation Act and the corresponding energy efficiency improvement targets set by the Federal Energy Administration. See Federal Register, Volume 42, No. 136, Friday, July 15, 1977, starting at page 36648. Seems likely, especially this bit: > [@](#): > > and improved coupling between the magnetron and the food. ---
**Author:** ![wolfpup](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/wolfpup/32/10618_2.png) [@wolfpup](https://boards.straightdope.com/u/wolfpup)\ **Post date:** [September 29, 2020, 12:39am UTC](https://boards.straightdope.com/t/aluminum-in-post-1980-microwaves/921757/23 "2020-09-29T00:39:12Z")
> [@squeegee](#): > > > [@wolfpup](#): > > > > like the fact that all or most of the bottom of the aluminum tray should be covered with the food, so microwaving a half-used portion could be bad news > > The picture I posted in the OP was the result of nuking a half used portion. Worked fine, microwave didn’t open any wormholes or nothing. The picture shows most of the bottom of the tray covered with sauce and miscellaneous other ingredients. Don’t know how much that matters but I think the general idea is that a bare flat aluminum surface will reflect microwaves back up into the magnetron, while any sort of covering with any water-containing material will absorb the energy. This is purely a WAG and just extrapolating from the first cite. The other gotcha IIRC is that the edges of the aluminum tray should be at least 2 cm from the walls of the microwave. Some of the large-size portions I’ve seen have aluminum trays that may exceed that, especially in small microwaves or if not exactly centered. ---
**Author:** ![squeegee](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/squeegee/32/14537_2.png) [@squeegee](https://boards.straightdope.com/u/squeegee)\ **Post date:** [September 29, 2020, 12:41am UTC](https://boards.straightdope.com/t/aluminum-in-post-1980-microwaves/921757/24 "2020-09-29T00:41:19Z")
> [@wolfpup](#): > > The picture shows most of the bottom of the tray covered with sauce and miscellaneous other ingredients. Right, but before cooking the left side of the tray had no food or cheese or juices in it. That they’re there at the end is from heating the dish. I’d lifted out the first enchilada onto a plate the day before and cooked that solo; this morning I cooked the rest in the tray. ---
**Author:** ![jnglmassiv](https://avatars.discourse-cdn.com/v4/letter/j/f07891/32.png) [@jnglmassiv](https://boards.straightdope.com/u/jnglmassiv)\ **Post date:** [September 29, 2020, 2:42am UTC](https://boards.straightdope.com/t/aluminum-in-post-1980-microwaves/921757/25 "2020-09-29T02:42:20Z")
> [@wolfpup](#): > > The other gotcha IIRC is that the edges of the aluminum tray should be at least 2 cm from the walls of the microwave. Some of the large-size portions I’ve seen have aluminum trays that may exceed that, especially in small microwaves or if not exactly centered. When I bought my house, the old range had an overhead (inoperable) microwave. It kept time using a [flip clock](https://en.wikipedia.org/wiki/Flip_clock). When it came time to replace it, I wound up literally disassembling the microwave top half since it was so heavy. Inside, I found factory stamps making clear the date of manufacture was in 1981. Anyway, the point of the story is about how small the cooking chamber was. A tray like OP’s would barely squeeze in and it might well have not cleared the front and back of the chamber if using the [aftermarket, windup turntable](https://americanhistory.si.edu/collections/search/object/nmah_1321698). ---
**Author:** ![Ruken](https://avatars.discourse-cdn.com/v4/letter/r/f475e1/32.png) [@Ruken](https://boards.straightdope.com/u/Ruken)\ **Post date:** [September 29, 2020, 2:59am UTC](https://boards.straightdope.com/t/aluminum-in-post-1980-microwaves/921757/26 "2020-09-29T02:59:14Z")
> [@Chronos](#): > > I’d be surprised if any practical metal product, of any sort, is made of a pure element, without any deliberate alloying at all (discounting bullion coins and the like as not being practical). > > That said, 98.5% is pretty close to pure. Obviously “pure” is a degree of how many nines one insists on. But with aluminum, the stuff that comes out of the electrolyzer tends not to be desirable. The additives required depend on the application. More than most people want to know can be found here: > **[Aluminium alloy](https://en.m.wikipedia.org/wiki/Aluminium_alloy)** > > An aluminium alloy (UK/IUPAC) or aluminum alloy (NA; see spelling differences) is an alloy in which aluminium (Al) is the predominant metal. The typical alloying elements are copper, magnesium, manganese, silicon, tin, nickel and zinc. There are two principal classifications, namely casting alloys and wrought alloys, both of which are further subdivided into the categories heat-treatable and non-heat-treatable. About 85% of aluminium is used for wrought products, for example rolled plate, foils... ---
**Author:** ![Melbourne](https://avatars.discourse-cdn.com/v4/letter/m/b5e925/32.png) [@Melbourne](https://boards.straightdope.com/u/Melbourne)\ **Post date:** [September 29, 2020, 8:44am UTC](https://boards.straightdope.com/t/aluminum-in-post-1980-microwaves/921757/27 "2020-09-29T08:44:54Z")
Looking at the patents, I think the phase modulator (‘the fan’) was introduced about then. So before then, food tended to heat unevenly, and metal trays could make it not work at all. When they did have fans, it was just to move air around. I don’t personally remember. My family didn’t have a microwave then. ---
**Author:** ![MindsEye\_Watering](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mindseye_watering/32/3619_2.png) [@MindsEye\_Watering](https://boards.straightdope.com/u/MindsEye_Watering)\ **Post date:** [September 29, 2020, 12:58pm UTC](https://boards.straightdope.com/t/aluminum-in-post-1980-microwaves/921757/28 "2020-09-29T12:58:21Z")
I wonder if all of the above applies ONLY to aluminum, and not to other metals like stainless steel. ---
**Author:** ![OldOlds](https://avatars.discourse-cdn.com/v4/letter/o/a3d4f5/32.png) [@OldOlds](https://boards.straightdope.com/u/OldOlds)\ **Post date:** [September 30, 2020, 12:44am UTC](https://boards.straightdope.com/t/aluminum-in-post-1980-microwaves/921757/29 "2020-09-30T00:44:19Z")
When I got married in 1999, and we were broke, my aunt gave us her 1978 GE Microwave. With the simulated wood grain, of course. It became a point of pride to me that we continued using that until about a year ago, when my wife finally won the “we need a new one” argument. I actually really liked that microwave. ---
**Author:** ![hibernicus](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/hibernicus/32/2802_2.png) [@hibernicus](https://boards.straightdope.com/u/hibernicus)\ **Post date:** [October 3, 2020, 2:31pm UTC](https://boards.straightdope.com/t/aluminum-in-post-1980-microwaves/921757/30 "2020-10-03T14:31:20Z")
Wine bottle capsules (on more expensive wine; cheaper bottles might use PVC capsules): [http://puretincapsules.com/](http://puretincapsules.com/) [Previous page](https://boards.straightdope.com/t/aluminum-in-post-1980-microwaves/921757.md?page=1)