An air activated marking pen for drawing fine lines on dark fabrics.   As the ink dries on the fabric, the white marks will become more visible.

Markings disappear upon ironing or spritzing with water.  One of my favorite pens for drawing sashiko designs.  It won't rub off - non-messy!  

Always test any marker on a small piece of fabric before using.  Some sizings may prevent the marks from washing out.