KCMYWhile for most bookwork 4-color printing inks will be laid down in the sequence KCMY (black, cyan, magenta, yellow) exceptions are made depending on the nature of the copy to be printed and individual pressroom preference. Black is quite often printed fourth. As far as the ISO standard is concerned, only the CMY sequence is specified. Printing black last will tend to give the blacks in your halftones a greater intensity than if they were run first. The Print Guide site gives a full discussion the issue, and shows a couple of interesting examples the effects of changing the sequence and the press. The tack of the inks needs to be adjusted to go in sequence, with the stickiest laid down first.

a0064122_4c09094e08c20This diagram of 4-color sheetfed offset printing in CMYK sequence is in essentials little different from the web presses most people are familiar with. The difference of course is that the paper is being fed in as sheets not as a continuous roll. Also this press is not perfecting: the sheets printed on one side will need be stacked and then put through the press again, so the backup can be printed.