A wonderful pen designed to make adding those pattern markings onto fabrics easier. Simply mark out your notches rather than cutting into fabrics (or using other methods such as tailor tacks) and you can see where to match up fabric pieces.
The pen is deisgned to fade in 48-72 hours, or you can remove sooner by wetting with a damp cloth. Whatever you do, don't iron it! The marks will stay, which doesnt matter if they are in your seam allowance but not great at the end of a bust dart!
