I've been looking into this Sharpie+mug+350 degrees craft and it looks as though many people have been experiencing fading or the colors coming off altogether. Therefore, I would like to share this blogger's page. She explains to the tee how she cooked her mug at 425 for 30 minutes and then left the mug to cool in the oven. The results: a permanent cup at last! -- good because I did this once at 350 and the sharpie washed off!