Offset printing is a common printing technique in which the inked image is transferred from a plate to a rubber blanket and then to the printing surface. Specifically, printing plates must have ability to transfer an image to paper or other substrates. Printing plates are usually made from thin metal sheets of aluminum. Whatever the artwork is that is to be printed is split into the four main colors of CMYK (Cyan, Magenta, Yellow and Black) digitally. The image is then put on the printing plates four times for each color with photochemical, photomechanical or laser engraving processes. In offset printing each color of ink is applied separately - one plate per color.
Once each plate is made, the Pressman then mounts them to the plate cylinder inside the print press. Small dots of the four inks - cyan (blue), magenta, yellow, and black (K) - are deposited in specific patterns that make our eyes believe we are seeing a wide range of colors. That's why the standard offset printing process is often called 4-color process lithography or 4-color printing.
The advantages of traditional commercial offset printing are higher quality and the best cost-effectiveness for quantities over a few hundred, especially high volume quantities.
Low price per piece. The more you print, the less you pay per piece, since most of the cost is in the setup. With a commercial printer, any additional quantity costs only a few cents per sheet for the paper and ink.
Brilliant quality. Offset printing produces rich, accurate color and high-quality images and photographs, with sharp typefaces and fine details.
When you need 250 to 500 or more business cards, postcards, posters, glossy brochures, flyers or catalogs, offset printing is tough to beat for high-end quality at an affordable price. 4 color offset printing enables small businesses to compete with the "big guys" by providing professional-looking marketing materials.
To start a press run, the imaged plates are clamped onto the plate cylinders and the ink settings are adjusted for the density of ink needed for the particular run. The press operator then runs a batch of initial sheets through the press at low speed and carefully checks alignment of the colors and the ink/water balance to ensure perfect ink flow for accurate color reproduction. The plate positions and ink density can be adjusted while the press is running at low speed if necessary.
If you didn't know how offset printing was done, it's better plate than never!