CONTACT PRINTING

A contact sheet comes from the old days of film photography, where negatives would be pressed against a sheet of photographic paper and exposed so that you’d get lines of thumbnails of every image on the film. You get something similar when you place an order with an online digital printer, too. Large format film, many inches along each edge, could be contact printed to provide a useful print, but the small negatives of 35mm film produce contact prints most useful for evaluation purposes.

The same technique was once used to create printed circuit boards. A photo-resist—light-sensitive material—is painted on the board, and the “artwork” (the pattern to be etched on to the board) placed alongside and exposed to light, while a solvent is applied to the board. Where the artwork blocks the light, the photo-resist blocks the solvent, so the areas exposed to the light are dissolved away, leaving the artwork pattern etched on to the board.