Offset printer

Offset printing is a commonly used printing technique where the inked image is transferred (or "offset") from a plate to a rubber blanket, then to the printing surface. When used in combination with the lithographic process, which is based on the repulsion of oil and water, the offset technique employs a flat (planographic) image carrier on which the image to be printed obtains ink from ink rollers, while the non-printing area attracts a water-based film (called "fountain solution"), keeping the non-printing areas ink-free.
Using an offset printing press to print on paper was probably done first by Ira Washington Rubel, an American, in 1903. The inspiration was an accident. While operating his lithographic press he noticed that if he failed to insert paper the stone plate would transfer its image onto the rubber impression cylinder. When he then placed paper into the machine it would have the image on two sides, one from the stone plate and one from the rubber impression cylinder.
To Rubel’s amazement, the image from the rubber impression cylinder was much clearer; the soft rubber was able to give a sharper look than the hard stone litho plate. Soon he created a machine that repeated this original “error”. This process was also noted by two brothers, Charles and Albert Harris, at about the same time. They produced an offset press for the Harris Automatic Press Company not long after Rubel created his press.
The machine created by the Harris Automatic Press Company was based on a rotary letter press machine. A cylinder was wrapped with a metal plate that was pressed against ink and water rollers. Just below the metal plate cylinder was a blanket cylinder. Below that was an impression cylinder which fed the paper against the blanket cylinder so that the image could be transferred. While the basic process in offset printing has remained the same, some modern innovations include two sided printing and using large rolls of paper fed into the machines.