I have never personally cleaned mine. I have heard of one method which I still haven't had the nerve to try yet!
Take the curtains down, remove all the hooks, then use rubber bands to kind of hold them together loosely, and using woolite wash them on a gentle cycle using cold water in your washing machine. Do not put in dryer but spread them out and hang up to dry outside.
Not my recommendation so I have no input as too how well it works, guess that's why I am apprehensive still...and afraid they may fall apart from age....LOL!
2001 Beaver Contessa Naples 40
2012 Cadillac Srx
retired AirForce 1979-1992