I came up with a stupid answer, and tried to delete this post, but it didn't work. Hold on while I think of something else...
EDIT (to save bandwidth...I know, Saucie would be so proud!

): K, got something: Frodo's mithril vest was the only one that didn't hurt the "bad guy". The Silmaril burnt Morgoth and Ungoliant (Right??? Sorry, it's been so long! *sheepish grin*), Sting, well, obviously, and the Phial burnt Shelob's eyes.
P.S. Sorry to keep you waiting Perky!