Water erasable extra fine tip blue pen. Do not iron before you have washed the markings away completely or they may become fixed. Test it on your fabric first just to be on the safe side, but I have used it on cotton and cotton linen and it worked fine.
Open since 2005, but currently online only, A Threaded Needle is located in British Columbia, Canada. I am always happy to hear from you by e-mail firstname.lastname@example.org