Vellum is a lovely medium to use in paper craft and collage. It comes in a wide variety of colours and with patterns but all of the vellums shares one basic feature - they are translucent. You can build up views within a collage by layering vellum over other items, cutting away areas and even stamping/ marking on top of the vellum. My favourite use at the moment is to create butterfly wings out of vellum. They are so light and fluttery.