We have just bought new curtains (www.next.co.uk/x544114s1#) for our living room and I have today noticed a dirty mark (which looks suspiciously similar to the shape of DS mouth) on them :( I have tried to use a damp cloth to clean the mark but it has now left a nasty water mark on them. Any ideas how I can get this out? I can't see any washing instructions on them or the website so no idea what to do now.