I like to use a sliver of soap on darks. It stays on longer than chalk and comes out easily. However, I am a machine quilter so I do fairly minimal marking and generally get the quilting finished within a few days of marking so I don't have experience with leaving soap markings in for any length of time.
You can can sharpen up the soap sliver when it gets dull by either washing your hands with it and set it aside to dry (what I do) or some folks use a cheese grater to sharpen.
Rob
Last edited by rryder; 04-24-2017 at 04:35 AM.