With all the applique I've been doing, I discovered that I've got a dirty iron. I've been trying to clean it after each use, but I've got some sticky stuff that is turning black. My mother-in-law thought I was nuts when I asked for a Rowenta Iron for Christmas and I don't want it ruined. How do I clean it? I thought about Goo-Gone, but it will leave a oily residue. What do you recommend?