Offset printing uses metal plates and rubber mats to transfer ink onto paper, allowing for efficient and flexible mass production. Images are created on a computer and burned onto metal plates, with ink added one color at a time. The CMYK spectrum is used to create all colors, with options for different backing materials.
Offset printing, sometimes also known as “offset lithography,” is a very common modern printing method that involves setting images and words onto paper through a series of metal plates and rubber mats. It is very efficient and almost always computer driven. The method is called “offset” because the material to be printed is not pressed directly onto the page or other support, but is first distributed on a metal plate, then on a rubber mat, and only then impressed. Ink is usually evenly distributed by an internal jet system and can automatically assign different colors to different regions as directed by a computer management system. These machines generally offer a lot of flexibility when it comes to what, exactly, is printed; most can handle anything from newspapers and glossy magazines to CDs and fabrics of various thicknesses. Users typically have to reset the machine and tweak its controls to get different results, but in general the devices are quite flexible.
Printing machine basics
The main idea behind a printing press is efficiency. Presses allow for the mass distribution of a wide variety of materials. Once the creators design the original, the machine does the rest, making as many copies as needed. Compared to today’s options, the original presses were quite cumbersome to operate. Technicians had to set each letter on each page individually, then apply ink; only then could the paper be pressed on top, making an imprint. This method was even more efficient than individually stamping or inscribing each page, as once the presses were set up more pages could be printed relatively quickly; getting there, however, often required a great deal of patience and discipline. The offset method is a modern improvement on these largely manual machines.
How the offset method works
In offset printing, the ink is not pressed directly onto the paper but is spread from a metal plate onto a rubber mat where it is then fixed and pressed. The images to be printed are created on a computer and then “burned” onto metal plates using a chemical development process similar to photography. From here the metal plates are moistened with water, which adheres to the image-free areas; the ink is added later, one color at a time, where it sticks to the areas with images.
Most modern systems use a direct-to-plate system where images are burned directly onto the metal. Omitting the secondary step saves time and money, although the overall quality may be lower.
Color spectrum
The colors used in offset presses are usually cyan, magenta, yellow and black. Each color is represented by the first letter of its name except black, which goes from “K”; the resulting spectrum, therefore, is often listed in the literature as CMYK. K is used to represent black to ensure there is no confusion with blue, which is usually assigned to ‘B’.
Different percentages of each color in the CMYK spectrum create virtually all colors used in offset printing. There are color matching systems, such as the PANTONE® system, that allow print buyers to see color. The code for that desired color can then be entered into the offset printer’s computer and it will calculate the percentages of each color that are to be used.
Paper and printing options
There are a couple of different options when it comes to the backing i.e. what the machine is actually using as material for printing. Sometimes the device uses the so-called “web” printing press, which uses huge rolls of paper that are fed continuously; most machines can also use a sheet-fed press which, as the name suggests, uses single sheets of paper. Alternatively, even non-paper items, such as multimedia content, can usually be printed on cut-sheet devices.
In general, the offset method uses all the latest printing technologies, including computers which aid in the design. Computers are also used to generate instructions for mixing ink colors and distributing them on paper.
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