Lithography is a chemical process and works on the principle that water and oil do not mix. There are several steps involved in the process from design to receiving an actual printed product. The basic process of Lithographic Printing involves images being put onto plates, which are then dampened, first by water, and then by ink. The ink sticks to the image area, and the water to the non-image area. This image that has been created is then transferred to a rubber blanket, and finally onto the paper.
Now lets go into a little more detail on the technical side. So how are the images put onto plates I hear you asking. The Lithographic Printing process is similar to the process of developing photographs. Images from the negatives are transferred to printing plates, a controlled amount of light is allowed to pass through the film negative to expose the printing plate. With this light exposure a chemical reaction occurs, allowing an ink-receptive coating to be activated.
Different materials can be used for the plates, depending on the quality of product required - Paper plates can be a cheap option to use, however produce lower-quality results, Aluminium plates are more expensive, but they give a better quality finish. There are only four colours involved in the Lithographic Printing process - Cyan, Magenta, Yellow and Black (Also known as CMYK) - these colours are all mixed together to make many different colours.
The reason that the image is transferred from the press to a rubber blanket as opposed to transferring it straight on to the substrate is because if the image was directly transferred onto the substrate then the substrate would be moistened. The rubber blanket is basically a cylinder covered in rubber, its job is to squeeze away the water and pick up the ink. The cylinder is rolled over the paper to transfer the ink, giving you your final image.
Now why would you choose Lithographic Printing over Digital Printing? What are the main benefits?
- Very-cost effective for long print runs - economies of scale, the process is very efficient once a press has been setup.
- Unrivalled print-quality - Lithographic Printing quality is by far superior to Digital Printing quality.
- Flexibility - most flexible method in terms of printing stock, inks, and finishes.
Now when somebody asks you what you know about Lithographic Printing (or Offset Printing for that matter, seeing as its the same thing!) you should be able to explain them a thing or two!