Look in the Bugs thread. Some guy was complaining about his copper and tin disappearing while he was at the forge. Apparently, he had opened the menu for the forge. Instead of going to the craft menu to the right of the center of the screen, he decided he needed to Ctrl + left click on the copper and tin in his inventory to make bronze. According to him, his copper and tin disappeared out of his inventory. Gone forever.

I'd be willing to bet that they are not gone forever. They are probably lying on the floor behind his forge. But perhaps he is correct. If he is, all you have to do is load up you inventory with the stuff you want to get rid of and go to the forge. Ctrl + left click on the lot.