Offset printing uses a series of rotating cylinders to apply the ink to paper. Each ink colour on the Offset press has its own set of cylinders. For full-colour projects, the inks are applied in successive layers to create the final image.
The first cylinder has a printing plate formed around it. Usually made of plastic or thin aluminium, plates are custom made for each print job and contain the images that will be transferred to the paper. The plates are treated so that certain areas attract ink while other areas attract a water solution. As the Plate Cylinder spins, the ink is distributed onto the plate. The water solution is also distributed onto the plate. Because the plate has been specially treated, the ink adheres to the image areas while the water solution repels ink from the non-image areas.
The next roller in the sequence has a rubber blanket around it. This roller is called the Offset or Blanket Cylinder and turns in the opposite direction of the Plate cylinder. As the Plate cylinder rolls against the Offset cylinder, the water on the plate is squeezed away and the ink on the plate is transferred to the rubber blanket. The Offset cylinder receives a mirror image of the ink design to be printed.
The final roller in the sequence is called the Impression Cylinder. It turns in the opposite direction of the Offset cylinder. It presses the paper against the rubber blanket to transfer the ink to the paper. The image on the paper is now identical to the image on the plate.
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