The ability to melt metallic items into ingots is great, but it's a pain to use nowadays. You'll of course want to select all your gear of a certain metal at one go to get a goot set of ingots. But pick a single one which is made of another material, and your entire selection is gone. I suggest that it should be changed so that there's some on-screen warning (such as with trying to unwield a cursed weapon) about the mismatching metals instead, so that you can go on and pick and choose with your selections intact.

EDIT: ixi's idea is simply better, so please allow selection of several metals and just let it yield different types of ingots as an UI enhancement. It's fine if the melting time is multiplied with the amount of metals involved, to simulate that they are actually done separately.