I use the Bohin mechanical pencil with white lead on my dark fabrics. I find it stays on well during the quilting process but washes out with no issues. On light fabrics I usually just use a #2 mechanical pencil. But if I think of it next time I'm in a LQS that sells the pencils and leads, I'll get a different color for the light fabric as I'm hoping it will wash out a bit better. As long as I don't get too heavy handed with the #2 lead, it's okay. I have also evolved to marking as I go most of the time vs marking the entire quilt. I personally have not had much luck with the soap slivers or typical 'taylor's chalk'. I have issues with them fitting into the stencils.