Offset Litho Printing
Often referred to as CMYK or Full Colour, Offset Litho is a traditional method of printing used for larger print runs and works on the principle that oil and water do not mix.
In Litho, all print is made up of a series of minuscule dots of varying sizes that when viewed together give the appearance of the different colours. These dots consist of the four basic printing inks: CYAN (bright blue) MAGENTA (bright pink) YELLOW and the Key colour Black (CMYK). At the pre-press stage artwork colours are converted into these inks, so for example, green would consist of dots of cyan and yellow – but may also contain a percentage of magenta and black depending on the shade.
Photosensitive aluminium sheets, known as ‘Plates’ are created for each of the ink colours. The Plates are inserted into the press by clipping onto a roller. Each plate is coated with its corresponding colour by a smaller ink roller. The coloured image is rolled or ‘offset’ onto a cylinder (blanket), which makes an impression on paper being fed through the press. The colours are laid down one by one onto the sheet and create a full colour image on the page.
Traditionally, individual SPOT colours were used and were limited to one or two as printing was expensive. Spot colours are standardised using the PANTONE range which ensures consistency and generally come premixed straight out of the tin. Spot colours are important for companies who want to ensure complete brand consistency on all their printed material as the colour will be the same no matter where it is printed (the only difference that will affect the colour being the paper or board that it is printed on and any finishes). Spot can also can achieve colours that CMYK can’t, such as bright orange, fluorescent pink, gold etc.
Digital printing methods include inkjet or laser printers. These are very high quality versions of your office printer but on a much bigger scale and they often have the ability to cut, collate, and bind in one process. Some machines also have a facility to create individual mailshots by printing each item with the individual contact details from a database.
Unlike Offset Litho, the digital process does not use plates but deposits ink or toner directly onto paper. The cost per sheet is higher using digital but on shorter runs this is usually acceptable as there are no plates to include or machine set up time.
Digital Presses use CMYK process colours but they are applied at the same time. Digital printing is quicker than litho but cannot use SPOT colours.