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 Offset Lithography


Offset lithography became the most popular printing process during the 20th century. It was a much faster and more practical way of printing illustrations than previous methods.
Willys service information was printed using this method. Following is a step by step explanation for the printing process used to create a page from the Willys-Overland MX-735 Vehicle Modification Kit manual. This example uses page 17 which includes both text and an illustration.

 First a photo is taken of the item to be used in the illustration. A generator is also visible in the actual photo but it will not appear in the final illustration. Notice how the regulator wiring cover is being supported, off to the side, by a block of wood.

Click on the image for a larger view of the photograph.

This is the actual illustration artwork; it is called a "board". The photograph of the voltage regulator is glued to thick cardboard. In this case the background is painted white to remove the shadows, the generator, and the block of wood that was supporting the cover. Then the details are enhanced and highlighted by painting. The artwork is larger than the final printed size so minute details can easily be altered. Sometimes other photos are pasted on to include parts or details not present in the original photo. Inked text and arrows are also added. When the artwork is complete it may not represent anything that actually ever existed. Remember to keep this in mind when looking through Willys Service Information.

Click on the image for a larger view of the board.

The artwork is then photographically reduced to the proper size and applied to the "paste-up". The paste-up also includes the text portion of the page which may be simply typed in place. Another photograph is taken of the paste-up. This negative will be used to expose the printing plate. A printing plate is special thin aluminum sheeting with a light sensitive coating. When it is exposed and developed, the final image appears on the surface in an ink-receptive coating.

Here is a side view of a printing press. The developed printing plate is tightly wrapped around the top cylinder. The ink is applied to the printing plate near the top. Ink will only transfer to the ink-receptive coating since the water repels it from the remainder of the plate. As the press turns the ink image is transferred to the rubber blanket on the center cylinder. The ink on the rubber blanket is a mirror image of the final document. Paper is fed in between the rubber blanket and the lower cylinder and the ink is again transferred, this time to the paper.

And here is the final product, a page in the service information. Click on the image for a larger view of page 17.

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