According to "Making Money," why must designers create the appearance of paper money before engravers can do their jobs? Engravers arrange several "identical printing plates," so that a design can be created on each one. Engraving requires the use of "green and black as well as metallic and color-shifting inks," which designers create in their labs. Engraving is the "cutting of a design into a hard surface," so the design must be complete before engraving can occur. Engravers work on "steel forms called dies," which designers build with various carving tools.