I would hesitate to wash before I put them in a quilt. They are so beautiful that even the water marks do not take away from them. You could probably soak them and gently smooth them out and let them air dry. If you sewed them first and then washed, if the stain did not come out, it would just add a bit of character. I love vintage and have a very similar quilt at home that my aunt made. It is sashed in a soft yellow. Congratulations on a wonderful find.