A sliver of bar soap, such as Dove or Ivory. Completely washable.

I use this at times too, but find the lead a little hard to get a good line from it. For a refill last time I bought the Fons and Porter ceramic leads, same size and white and they work too. I found he yellow lead from Sewline particularly useless, too hard. :( The majority of the time I use the Clover Medium blue water soluble pen and the Clover white and blue water soluble pencils, a bit cheaper but less precise.

I had started to use Frixion pens, the lines iron right off! I knew that the lines might reappear in "in the freezer". Really, who would put a quilt in the freezer? Well, Iowa is running right at -20 right now, and it occurred to me that a quilt left in the back of a car would be in jeopardy. I am reading this post with renewed interest. :o

I agree with what Annaquilts says. I have used the first chalk product she lists with great success. I have evolved to a version of the second product...I have the Bohin version of that pencil...and a regular mechanical pencil with #2 lead.

I hand quilt and generally use purchased stencils. I have made my own stencils as well. Both of these products come off very easily, particularly when washed and work well with both purchased or made stencils. Since they are chalk based, they do have a tendency to wear off fairly easily so I now mainly mark as I go. Easier to do with hand quilting than machine I would guess.

With any of the products I've mentioned I've not had issues with marks not washing out. You need to test, obviously, not only for ease of removal but also to see what colors work best for you.

Just regular chalk. The pens are intriguing, but I worry about what would happen to the fabric in twenty years time. Too chicken to try them.

Warning! The fritz water soluble marker won't come out of pink or red fabrics...I learned the hard way.

Wait! It's the Dritz....not the fritz!

Crayola washable markers. Cheap, wash out totally.

Bohin pencils for me. Both the thicker and the thin mark well and wash out. Refills in various colours are available. The sew easy I found to hard to leave a clear mark. Also have used lead pencils the best of which was purchased from Harrods in the UK. Now needing a replacement as it is down to an inch and a half!!

"White Marking Pen <Fine> Clover" is what I use on dark fabric. Irons out nicely. It does take a few seconds to appear after marking, which is a bit annoying, so I might get one of the F&P white marking pencils. For lights and colors I often hear that people like the Crayola washable markers, but do they make a thin line? I use Frixion pens but don't like that the marks come back in the cold, I sometimes take quilts other places to share when freezing outside and don't like worrying about the markings.