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Colour mixing for print

We begin this tutorial by looking at what the technical term overprinting means and how it works in practice, and then we show you how to create a record cover in Adobe Illustrator CS2 using three special PMS (Pantone Matching System) colours: two fluorescent colours and one metallic colour, overprinting one another to create remarkable visual effects and new, unexpected colours. Finally, we explore the process of sending overprinted artwork to the printers and the checks that you can do in Acrobat 7.0 Professional to ensure a good result.

When creating artwork for print in a design application, the default setting is for one on-screen object in a flat colour to knock out its shape from an object of flat colour beneath it. This is because printers don't like to have flat colours overlapping as it slows down the rate at which the inks dry. So when the artwork is output to separate printing plates, the edges of the objects sit next to one another but the colours don't mix. If, however, you set the objects to overprint, both objects retain their full shape when output to printing plates and, when the plates are printed sequentially in the chosen colours, the top object overlaps the object beneath. Because most ink is translucent, a third colour is created where the objects overlap.

Until the middle of the 20th century, most printed colour imagery was created using complex hand-rendered overprints of sometimes 10 or 20 colours to reproduce images in a process called lithography. Printers and technicians have long been masters of overprinting, but it wasn't until the mid-20th century that designers began wilfully using overprinting as an inventive image-creation effect either through a desire to experiment or often as a technique to expand the colour palette when budget constraints allowed for a limited number of printed colours. Now that CMYK printing is usually cheaper than two-colour printing, the use of overprinting PMS colours is something of a luxury.

The computer screen is unable to reproduce exactly what will happen when overprinting techniques are used. This makes it an intriguing process and puts the designer back in touch with the physical process of printing. The designer has to use their experience to imagine how the combinations of colour, ink translucency, paper density and finish will interact with the printer's skills and machinery to create the final image. A leap of faith is required, which is rare in today's automated digital environment, and it's that embracing of the element of chance in combination with exposing the process of printing to the viewer that can really breath life into your printed work.

Follow the download links for our in-depth tutorial on mixing colours and preparing a record sleeve for print.

Click here to download the support files ( 3MB)

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