What do the terms "first surface" versus "second surface" mean in printing?
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.
There are aesthetic reasons, as well as durability concerns, with some first surface applications. For a storefront, window graphics on the first surface will be exposed to weather which will shorten their life span. Indoor graphics don’t face wind and rain, but they can be more attractive if they show off their clear substrate surface. This is where second surface printing and mounting come into play. Second surface reverses the first surface process. The graphic is printed or mounted on the back of the clear substrate. This allows the substrate to act as a protective layer.
There are two methods to consider. Second surface mounting of opaque graphics simply involves adding a window adhesive to the print face and mounting it to the back of the clear substrate. This can also be called face-mounting. For second surface printing directly to a clear substrate, the process is different. The image will first be mirrored. Then the color ink will be printed first, followed by the white ink on top. The graphic will be right-reading from the viewing side. Second-surface printing can also be done on PSV or window clings so they can be adhered to the inside of a window and seen as right-reading from the outside.