LEFT: How a basic conventional litho printing press works.
The common Litho process works as follows:
First we need to know what principle the litho process works on so we can better understand how the process works. The litho printing principle is based on the fact that water and oil do not mix.
In the above diagram you will see the basic inner workings of a standard litho printing press. The ink used for litho printing is a very thick oil based ink, kind of like coloured grease. This ink is placed in the ink duct wich is slowly and gradually transfered onto a series of inking rollers. These inking rollers help to smooth out the amount of ink so that by the time it reaches the plate cylinder the ink is a very thin film.
The ink is then transfered onto a positive plate which is attached onto the plate cylinder. See the image on the right, this is a positive plate. Where there are green areas, is where the ink will stick to, the places which are left blank is where the water will effect. Now this is where the litho principle comes into play. The water repels the ink where the blank or white spots are on the plate and the green areas of the plate repel the water so that the green areas stay dry and assist in picking up the ink. As you will see in the diagram above, the plate cylinder makes impact with the inking rollers as well as a water dampening system. The water dampening system contains a water trough with chemicaly treated water in it together with a series of rollers which impact on the plate cylinder.
The plate cylinder carries the ink onto the blanket cylinder and no, they did not make a blanket cylinder to keep the machine warm in winter, the blanket cylinder is a cylinder which has a rubber sheet covering it. the rubber sheet is known as the blanket. This rubber sheet picks up the ink and transfers it directly onto the paper.
There is another cylinder underneath the blanket cylinder otherwise known as the impression cylinder. This cylinder can be adjusted to accomodate the thickness of paper and the amount of pressure wich is applied to the paper from the blanket cylinder.
In order to do full colour printing, this process is repeated 4 times. Hence the term CMYK. First is "C" or cyan ink, this is a light blue ink which is applied first. Second is "M" or magenta ink, this is a dark pink ink which is often applied on top of the cyan print. Next is "Y" or yellow ink, this is a rich deep yellow which is applied on top of the Cyan and Magenta prints. Lastly is "K" for black, don't ask why the made it K instead of B, I don't know, thats just the way it is. The black ink is the last to be printed, this also helps give the full colour prints their contrast.