This erasable pen set comes in handy when drawing seam allowances and other markings. The blue ink erases easily with water and the purple ink disappears in 2-14 days. These pens are perfect for drawing seam allowances or creating other temporary markings on your fabric! The ink in the blue pen can be erased by water while the ink in the purple pen is design to disappear within 2-14 days of application. For use with ScanNCut Pen Holder (not included).