How Offset Printing Works

Sometimes, especially when they visit our facilities at, customers ask us how offset printing works. The offset printing system is quite unknown even for people whose work is usually related to printing, so let’s explain it very briefly

The offset printing process

Before printing…

Nowadays, the origin of the printing process is found in the computer, specifically in PDF files, normally generated from professional layout programs such as In Design. Then the information to be printed is recorded on aluminum plates: one plate for each color of the process color: cyan, magenta, yellow and black. The machines responsible for carrying out this recording process are the so-called CTP (Computer-to-plate, “from computer to plate”). From the CTP, the plates are placed on the printing machine.

To understand how offset printing works, it is necessary to know that the printing plate is coated on its entire surface by a layer of polymers that have the property of attracting (fixing) ink and repelling water. The bare surface of the iron, on the other hand, repels the ink and attracts water. And you know … water and oil (ink) never mix. For more information visit

The function of the CTP is precisely to make disappear of the plate that at the outset is totally covered with polymer the zones of the same that are NOT going to be printed. This is achieved by “burning” the surface of the iron with a laser.

Finally, the areas that will accept ink keep the polymer, while those that will not be printed, do not.

Inside the offset printing machine

Once the plates are created, this is the sequence of steps that will allow us to print from paper, ink and water:

  • Plates are placed on the plate cylinder (also called illustration cylinder).
  • A set of rollers (damping rollers) transmit a water-based solution from a bucket to the iron, moistening the surface. As we have explained, only the areas with metal in sight will accept the water.
  • Another set of rollers (ink rollers) transmit ink from another cell (inkwell) to the iron. The ink will only be fixed in the areas where there is polymer. The areas with exposed metal will repel the ink, since a thin sheet of water already exists on them. However, and this is another point that differentiates offset from other printing systems, the inked plate will not contact directly with the paper: instead a second cylinder called an offset cylinder is placed, covered by the blanket, an elastic surface based of rubber.
  • The ink passes from the plate cylinder to the blanket.
  • Ink passes from rubber to paper-The paper circulates between the offset cylinder and a third cylinder whose purpose is to exert the correct pressure that allows the printing and circulation of the paper at the same time.

The intermediate step from the blanket to the paper is necessary since if the paper were in direct contact with the plate the image would deteriorate immediately since the paper is a very abrasive material (and the image on the plate, very delicate).

Keep in mind that this process is repeated for each printing unit. To obtain a color image (four-color) the paper will then pass through at least 4 printing units. You can visit

And that’s how offset printing works!