The petticoat on the real costume isn't tulle. It's actually a really heavy synthetic sort of taffeta. So it's really stiff and because the petticoats are such a full pattern, they just provide a lot of volume on their own with no need for cording or hoop wires. The petticoat is two layers. The outer layer petticoat is just a very full pleated skirt - probably a mirror of the pattern used on the light weight outer skirt. It kind of serves as a lining I think since the outer fabric really is kind of transparent on it's own. The 2nd petticoat is several tiers of gathered sections (I think 3 tiers total) like a boho skirt. This kind of idea, but fuller. Oh yeah, the iridescent chiffon at Thai silks was not the right color at all. I did see some irredescent gray chiffon (non crinkled) in LA that would be a possibility if I wanted to go without crinkles. It might be what ladyamaryllis had used. I dunno, I still half hope that the creponne satin chiffon I got at Thai silks with the slight satin sheen is the right stuff. When I look at photos of the real costume that were taken up close it looks so darn similar to that! And maybe that's what they meant by 'iridescent' in Dressing a Galaxy? Not iridescent as in two tones of thread to make it 'shot', but iridescent in that is has a slight sheen to it.