Here's what I found for you:
After washing and rinsing the curtains (follow care-label directions), dip them in a sink full of water mixed with a cup of epsom salts (dissolve the salts with a little warm water, then fill the sink with cold water) and hang the curtains to dry. They should be as crisp as new! (without ironing).
I haven't tried it yet.Let me know if you do...
I've used this on my lace sheers. While it didn't make them 'crisp', it definitely added 'body" to the fabric, which they really needed.