Spot colours - or 'specials' as they're often called in the industry - are one of the last dark arts left in printing. The process of creating and managing spot colours for vector and raster images is shrouded in mystery, thanks to their inability to be cheaply hard-proofed, but with a bit of confidence - and Adobe Acrobat Professional - the process is actually very straightforward.
Spot inks can either knock out the background (which punches a hole through the CMYK inks ensuring the spot colour is crisp and vivid) or overprint the background (meaning that they sit on top of the CMYK inks and the colours blend). Previewing the different effects of knocking out and overprinting inks was virtually impossible until Adobe revamped how spot inks and additional channels were handled in Photoshop, InDesign and Acrobat.
And while it's still expensive and difficult to accurately hard-proof spot-colour jobs, soft-proofing spot colours has come on in leaps and bounds. Acrobat Professional enables you to preview individual plates, and the effects of different plates blending together has taken the crossed-fingers out of spot-colour work.
In this tutorial, we're going to create an A3 poster made up of a raster image with a silvery sheen and spot colour vectors. Remember, most printing presses are five-colour, so CMYK and a special can be printed in one pass. An additional spot colour or varnish will substantially increase the cost of the print job, because it must be passed through the press again.
