"Came out" refers to when they became in widespread use. That was in the 70's. As far as low power I can find nothing that indicates that it was ever ok to put

"Came out" refers to when they became in widespread use. That was in the 70's. As far as low power I can find nothing that indicates that it was ever ok to put tin foil in however I do know that in some cases you might put metal to specifically block cooking. So perhaps with a low power microwave there was no sparking etc. (I can't find anything on that and I don't see the link you sent showing that (which page is it on in the cookbook?). http://science.howstuffworks.com/aluminum-foil-in-the-microwave.htm http://science.howstuffworks.com/aluminum-foil-in-the-microw... http://en.wikipedia.org/wiki/Microwave_oven#Metal_objects http://en.wikipedia.org/wiki/Microwave_oven#Metal_objects http://mentalfloss.com/article/32032/why-cant-you-put-metal-microwave http://mentalfloss.com/article/32032/why-cant-you-put-metal-...