In addition to the CMYK colour system, some printing technology can use spot colours.
Spot colours allow you to print an image using less colours than CMYK and therefore print them more cheaply but it can also be used to control specific colours that need to be consistent throughout all your printed material such as your company’s corporate identity colour(s).
It is possible to print spot colours in addition to the CMYK colours process, so for example you could print a full-colour brochure that included an additional two spot colours for your corporate identity. You can print gradients of spot colours when printing lithographically and can also mix or blend two or more spot colours together on the paper. Spot colours can either be selected from the Pantone colour system or you can use one or more of the four CMYK colours.
Pantone is a colour system consisting of a wide range of pre-mixed inks allowing specific colours to be printed using only one colour channel rather than creating it from a mix of the CMYK colour channels. It also allows you to use colours that can not be recreated within the CMYK colour system such as Metallics, Fluorescents and some ‘normal’ colours that fall outside the CMYK re-produceable colour range
Spot colour printing is only available with offset lithographic and screen printing. It is not an option when using digital print technologies.
It is worth bearing in mind that the paper stock will usually be white, so this isn’t counted as a colour. However, any individual colour that uses an ink, including black, is considered a colour for the purposes of printing. If you are screen printing onto a dark material (such as a black t-shirt) then the press may have to print a white background onto the material before printing the other colours and as such the white would be considered an extra colour. In this situation, it isn’t normally required for you to include a white colour channel, the press will simply make their own as a composite of all the colours in the image.
How to set up a document using spot colours in Photoshop
To use spot colours in Photoshop you must use the colour channels panel. First delete any unnecessary channels (or add extra channels if you wish to use CMYK+Spots). Next double-click on the channel thumbnail in the channels panel. This opens a window with a colour swatch showing which colour the channel uses, double click this swatch to change the colour. From here you choose custom and then pick the desired Pantone swatch.
Note – when choosing a Pantone swatch you must use the Solid or Metallic swatch libraries. Coated and Uncoated both use the same inks, so picking this correctly isn’t critical, it will simply mean that the program will attempt to simulate how the ink will reproduce on coated or uncoated paper stock respectively but accuracy will vary depending on how your monitor is calibrated.
That channel will now be allocated to the chosen colour and any design elements you place in this channel will be output to the corresponding colour film.
If you only wish to use one colour, it is sufficient to simply design in Greyscale mode and then inform us of which colour you wish the image to be printed using.
How to set up a document using spot colours in Illustrator
Illustrator allows more flexible application of spot colours using the colour swatches pallet. However, this flexibility also means that it is easy to accidentally use other colours, so care must be taken to ensure that you have only used the colours you wish to use. Normal colour swatches in Illustrator will be made up of CMYK colour mixes. You can choose extra Pantone swatches by opening the relevant swatch library in the Windows pull down menu. Again, remember to only use Solid or Metallic swatch libraries. Selecting a swatch from the chosen library will add it to the Swatches pallet and from there you can apply it to elements in your document as you would with any other colour.You may specify Pantone Matching System (PMS) spot colours which provide more reliability in colour consistency than the colour blends available from the CMYK system. You should be aware that Pantone colours will still reproduce differently from paper to paper and the best way of ensuring a consistency is to match to a previously printed sample supplied to us to match to when we print.