In this article, we talk about Offset Lithography and why a basic understanding of this printing method can be useful in authenticating cinema posters. Nearly all original cinema posters are printed using offset lithography. Verifying that this printing method has been used is an important step in verifying the authenticity of posters. Offset Lithography uses printing plates. Fakes, on the other hand, are generally scans of original posters which are then printed using inkjet or laser.
The Offset Printing Process
Four colours are used when printing with offset lithography. The colours are cyan, magenta, yellow and black and they form the CYMK colour model. An offset machine will then have at least 4 Printing Units, each unit prints one colour. Colour is applied at multiple units and this gives movie posters their hugely rich range of colours. Look at the diagram below and you will see a unit for each of the colours used.
Diagram 1: A standard and simplified layout of an offset printing machine. Paper is fed in and is exposed to 4 different colours.
To understand how the process works, consider a situation where we wanted to reprint the Cinema Poster Gallery Logo as you see it below with the Cinema in Cyan, Poster in Magenta, Gallery and in Yellow and the background as black.
The image would be broken up into 4 digital files based on color separation. The design of the image and text would then be laser etched and transferred onto 4 sheets of aluminum called press plates. The 4 press plates for our revised Cinema Poster Gallery logo would look something like the below.
Diagram 2: A revised Cinema Poster Gallery logo and the 4 Plates that could print it.
The press plates are then mounted onto aluminum cylinders and create what is called the ‘Plate Cylinders’. Plate 1 is mounted onto a cylinder in the cyan unit, plate 2 is mounted in the Magenta Unit etc. The non-image portion of the plate cylinder is dampened with water rollers. This will avoid ink being passed to this section of the plate. Ink is then passed from the plate cylinder to the Offset (blanket) cylinder. The addition of this step creates a clearer sharper image. The paper is then passed between the offset cylinder and an impression cylinder, the cyan ink is added to the paper and the paper then carries on to the magenta unit.
Diagram 3: Typical Cylinders used in an offset print unit.
Why is Offset Lithography is important for movie posters?
The process we have just described is an oversimplification. Offset Lithography requires precision machinery that is not accessible to typical bootleggers. There is a photo of this machinery in the main article image. Skilled printers will produce color bars used for proofs that enable printers to revise and perfect the posters they print. Finally, consider that when a print run is complete the printer will destroy the offset plates used in the printing process. This results in the supply of posters being fixed after the print run is complete.
Diagrams 4 and 5:Â A colour bar from a printer’s proof and the full poster with colour bar.