The Offset Printing Process and Spot Colours

In Offset Printing, the image you want printed is burned onto a plate - a very thin piece of aluminum-like metal - and from there is transferred (or offset) onto a rubber blanket, then to the printing surface - paper or card. This process is called a "Lithography", and is based on the repulsion of oil and water. The image to be printed gets ink from ink rollers, while the non printing area attracts a film of water which keep the blank areas ink-free. 

This process is done using CMYK = Cyan, Magents Yellow, Black. A tray for each of these four colours is in the Offset Press and the ink is poured in. When the paper is pulled through the machine it prints one ink at a time so 'drying time' is required before the paper can be put back through for the second, third and fourth colours. If a Spot Colour is required many machines can add a additional ink trays, and the job can be put through a fifth time for the first spot colour, and again for any additional colours.

Spot Colours are colours that are found in commercially available colour ranges such as Pantone. These specific colours can be used in addition to CMYK (Cyan, Magenta, Yellow & Black) when C.M.Y.K. cannot achieve the desired colour. These spot colours are pre-mixed and can be added to the process as described above, by running the stock through the machine additional times, once for each colour. Spot Colours can also be Gold, Silver, Bronze, or other metallic colours.

The use of Spot Colours can be costly as a separate plate is required for each colour. For a normal offset printed 4 colour process job, four plates would be required.

Spot Colours can also be used instead of CMYK. If you wanted for example, a brochure printed in your companys' specific blue and green colours - that would only require two printing plates, and the machine that would print the job would need these two colours added into their additional trays - think of paint trays when using a roller to paint your house, but inserted into a machine.

To view the Pantone Colour range available, you would need to purchase a Pantone Colour Swatch book, which can be very pricey. A print & design store would let you see their books, which are available in 'Coated' and 'Un-coated' books, depending on what stock they have been printed on, which does change the colours. My tip for choosing a company colour would be to go to a paint store, take away some printed colour swatches that they have available for choosing house-paint, and just make sure that this is the colour you want when viewing under natural lighting. You can then take this into a print store and match it to the closest CMYK breakdown, or a specific Pantone Colour.

Discuss with your Graphic Designer what your future printing may consist of, because using a Pantone Colour could become costly if you have to add this colour each print run, rather than being able to print in a normal four colour print process.