Dritz Mark-B-Gone Water Vanishing Pen
Use these easy to see fabric markers to mark fine, clear embroidery designs, quilting and stitching lines on fabrics. The blue line is easily removed with a damp cloth or by spritzing cold water. IWe love these pens here at New Threads when we are working on customer quilts. Between them you can mark just about anything. We've tested them both and they work really well.
It is always a good idea to test ANY marking pen, no matter how good it is or how much you trust it, on a spare piece of fabric before you mark your project, just to be sure.