Seriously, it works! I use coconut coal, and in 2-3 minutes they become perfect for use. Of course I use an old, thrown out microwave oven, not the one I use to warm up food. The best is to find the amplifying points in the oven, where the coal will warm up faster. DO NOT USE THE STOCK GLASS PLATE, IT WILL BREAK FROM THE HEAT! Also I do not recommend putting the coals on the oven's metal surface itself, in many cases it has a plastic coating which will burn with a terrible smell. Use a ceramic plate or something non-metallic to put the coals on. Don't be afraid of flames, the microwave can excite the molecules of flame and create plasma. Yeah, it sounds crazy, and looks terrifying, but don't worry, it is all closed in a metal box, what can go wrong? Even safer than using electric coocking plates, where the coals can cause fire by flying sparks. If you leave a little space between coals they can make sparks with each other, which can make strange sounds, but are not dangerous, what's more, it heats the coal more quickly as these sparks are real hot. In many cases the bottom of the coals will heat up faster, so after 1 min you can rotate them. Good luck everyone! For the ones who are worried: yes, this can ruin the microwave, so do it for your own risk, best if you can get a hold on a working but old one. Also mind the smoke, which is normal when heating coals, only in this case all the smoke will come off them in half a minute, so it will be intensive! For those who asked how it works: the coal is electrical conductor, and in spite of many other material, coal's resistance gets lower by heating up, so the hotter they are, the more current waves will induce in them.