offset printing (aka offset lithography)
Offset printing is a method of mass production printing which consists of an inked image on metal plates being transferred or ‘offset’ onto rubber blankets or rollers then onto paper (print media). Offset printing is not anything like the direct printing Direct printing takes the image or text directly from the computer or electronic source to the printer. In offset printing, the computer makes the image on a plate as mentioned before. The offset process control, especially under the lithographic process. Lithography is a process based on printing from a flat surface and repelling all the ink apart from where you need it for printing.
Before printing, a printing plate is created for each printing ink, so there is a total of 4 plates for the 4 colours CMYK. CMYK which stands for Cyan, Magenta, Yellow and key (Black).
After they have been split each colour is then imprinted onto a metal plate on a drum. After that the drum stamps onto a rubber blanket (offset) cylinder where the paper is passed through the blanket cylinder and the impression cylinder. The paper passes through all the different colours before being stacked up together.
There are many benefits to using offset lithography one is that it is cheaper to print in heavy bulk. The ink, which fades and then runs out in direct printing methods, can be adjusted and controlled with offset printing. The person operating can twist some screw keys to adjust the amount of ink flow on the fountain roller. This minimizes the creation of wasted prints with insufficient contrast. Another reason is that the printing plates themselves are easy and fast to make with today’s technology and the plates each have the potential to run a million impressions or more.