I saw a glorious cyanotype on vellum by Emily Gomez at the Altered Views show at Lightbox Gallery in OR and promptly ordered some vellum to try. I like how translucent it is, but it will take a lot more practice to figure out how to maximize it. I didn't manage the shininess of the piece I saw in the exhibit, but I'm thinking about layering it over another kind of paper to get a holographic effect. You can check out Emily Gomez's work at http://www.emilyjgomez.com/. Her cyanotypes on vellum are so luscious. Check out the Altered Views show at http://lightbox-photographic.com/exhibitions/AlteredViews/. My own piece is #49. :)