At my guild meeting today, one of the members had just bought some pencils that are water soluble from a store for artists. Some were graphite that had not been treated with hardeners - we think. She also had a white one. I had never heard of actual graphite pencils that were water soluble. She tried them and they washed off with water with a tiny amount of dishsoap and a toothbrush.
Has anyone else heard of these?