So far, I don't think I'll be making the costume to go with this, although I have bought the velvet and filled a file with observations and advise from others. I really like the brooch, so decided to make one and somehow it turned into a few. Go figure!
What I used: What everyone else has been using and nothing new. Seed beads, bugle beads, sequins and fabric.
The trial brooch used: 5mm sequins -- blue
#2 bugle -- gunmetal
11/0 seed beads -- purple luster (which looks blueish)
dark blue cloth, thread and felt
The second brooch used: 5mm sequins -- blue
#2 bugle -- gunmetal
11/0 seed beads -- amethyst iris (multi colors in package)
dark blue cloth, thread and felt
I actually liked the second brooch much better and used the same materials for others.
You can find descriptions of how others have made theirs and a pattern or two by going to Padawan's Guide. I won't put up a pattern because others have done a much better job of drawing one than I ever could.
Backing: I used craft glue and glued a bit of fiber fill to the center of a piece of heavy artist cardboard that was cut to the brooch size. Glued the edges of the fabric to the back. To make the petal curves tighter than I could manage with just glue, I went around the brooch sewing the curves cross-wise, meaning I ended up with thread criss-crossing the back. Then, I added felt to cover it. Had to remind myself to sew the pin on before glueing the felt to the back.
Brooch observations from Dressing a Galaxy. There are 16 petals and they are a little smaller than the one I finished first, having only 7 slightly overlapping sequins in each petal. On my trial brooch, the end count was 10-14 sequins per petal. Also, it appears there are 2 rows of seed beads in the outlines and possibly seed beads filling in wherever sequins do not cover an area. Can't quite tell on that. The center of the brooch does look raised.