First, what kind of fabric is your costume made out of? Lots of fabrics will bleed/fade washout. Some will shrink. Also if you have alot of stonework/decorations, etc., you may want to find a reputable recommended dry cleaner - one who specializes in wedding gown preservation - who can take a look at your dress. It's pricey at best. Me? I know my own costume fabrics pretty well. And I don't recommend this for everyone. On some, I gently only wash the body/leotard by hand in Deft (for babies) or Ivory or Woolite in cold water. On others, I have had success, not recommended for everyone, on placing my costume in a pillowcase and making sure the pillowcase was not going to come open in the gentle soak cycle or a very closed knit mesh bag made for delicates, zipped it closed and gently washed/soaked the entire thing in cold water with woolite or Deft gentle liquid detergent. I then laid out the costume to dry, as carefully as a priceless sweater so as not to stretch it out. The stones that naturally fall off were caught in the mesh bag and I was able to re-apply them to the gown(s). Note: I know my fabrics and how they react in cold water plus I have alot of experience with stonework and decorations. SprialGrl offers good advice about circulation of air for your costumes and delicate fabrics.