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Color separation is the best way of printing in color. It is also called four-color process printing. It is based on the fact that all colors are made from the three primary colors (red, blue, yellow) and black is used for detail. Actually, the colors used in color separation are yellow, cyan (a shade of blue), magenta (a shade of red), and black. If you look at home you will see that these are the same colors used in the print cartridges for your computer printer.
Color separation is used in something called offset printing. This is a type of printing that uses plates made from a photographic image. (Also called photolithography). Four different photographs are taken of the picture or drawing that you're trying to print. In each photograph, a different color filter is used in the camera. You can guess that the different color filters are each of the primary colors and a fourth plate for black. The negatives that are made from the photographs are used as printing plates. They are used on a four-color press. The four-color press has a color plate cylinder for each negative. When the paper runs through the press, each plate puts its own color onto a blanket roller. The blanket roller puts the color onto the paper. What happens next is that the colors are mixed right on the paper itself! You can see that any color imaginable can be mixed just by how much or how little of each color is used. Today, electronic scanning machines can do color separation even better than the photographic filters. The scanner (which is connected to a computer) takes the picture or drawing and breaks it down into the three primary colors plus black. Then, these machines can make the photographic negatives or make printing plates.
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