Offset lithography was developed over 100 years ago as a method of mass production of printed items. The method was designed so that each copy of the printed item coming out the printer, would be identical to the other. This made the method suitable for printing newspapers and has since developed to undertake the capabilities of web printing - that is - printing on a giant continuous roll of paper, and it is this method of printing that is so vital in providing John Smith with his paper every morning. The machines can be as big as houses (especially for printing newspapers) and it can only be assumed that they are extremely highly maintained due to their upmost importance in printing the national news every day. As well as this extreme industrial standard of printing, the method is also used for mass production of other printed items such as posters and fliers, and basically any stock that will flow through the printing rolls. However, paper tends to be the most prominent choice of stock.
The process works by rolling 4 'etched' pieces of sheet metal that have the chosen design inked out on them (4 as each sheet constitutes the primary printing colours of cyan, magenta, yellow and key (black)). The process relies on water and oil to determine where ink should appropriately sit on said pieces of sheet metal. The design is inked onto a roller which subsequently rolls it onto a rubber roll connecting with it that finally prints it on the paper. The diagram should explain: