Solid areas of colour in particular solid black, can pose a problem if its not been set up correctly.
Most artwork we see is set up with full colour black, which means that the black is made up from within the full colour set, there will be a percentage of Cyan, Magenta, Yellow and Black.
This is fine if the whole colour make up is less than 200%, Eg 50% or less of all C,M,Y,K colours.
If 200% colour density is exceeded, then the paper its being printed onto will become saturated that its unlikely that the ink will dry properly. Should this be the case then this will cause ‘set-off’, which is where the ink transfers from one print to another, which is a huge problem.
With regards to solid black areas, the crucial colour is obviously black, more often than not solid black areas have the black set to less 100% which means it will never achieve full 100% black.
If a black solid area only consists of black ink only then the result can be quite dull and becomes a matt black, even on gloss paper.
So other colours can be added into the mixture can help to ‘deepen’ the black, this is whats known in the trade as ‘Rich Black’ and needs to be made up of the following.
For a deep black, 100% Black (K), 50% Cyan (C), there is some room for a small percentage of magenta here too but never any yellow!. Yellow can make the black appear grey as it lightens it. On screen this will look fine, but if any percentage of yellow is added then this will water down the black, similar to adding white to it, so try to avoid yellow being present if at all possible