What do the terms "first surface" versus "second surface" mean in printing?

FIRST SURFACE. The first surface of a clear substrate refers to the side facing the viewing audience. Whether it’s a store window or wall-mounted graphic, first surface printing or mounting means the graphic will be on the viewing side of the substrate. An important consideration when printing to clear substrates is white ink. Digital printing relies on the color of the substrate (primarily white) to provide opacity and color saturation. When printing on clear substrates, graphics will appear translucent and washed out without that white backing. The solution is to add a white ink layer under the color ink. This allows the graphic to retain transparency where needed while providing a white backing layer for the color ink. In this first surface printing example, our clear substrate will receive a white ink layer followed by a full color layer. All the ink is on the first surface, or the viewing side. There are applications where this may, or may not, be desirable. SECOND SURFACE. There…