To Overprint or not to Overprint? Black is the Question!

To compensate for misregistration on a press, printers often ask that the colour black be set to overprint so that any misregistration cannot be seen.

However, black fills placed over coloured panels or scans which have overprinted can still be seen through the black ink. Overprinting black is recommended for lines under 2pt thick or type under 60pt, not necessarily for all black fills.

This is a particular concern in Adobe InDesign as by default, all solid 100K generated in the InDesign using the [Black] swatch (that is, not in graphics placed into InDesign) will overprint unless the default is changed in the preferences.

When placing black fills, consider what is underneath the black overprinted fill. If the job is CMYK, consideration may also be given to using a “rich black” which will give a dense black and prevent the black from overprinting, knocking out whatever is underneath the fill.

If a black DOES need to knock out while keeping all other blacks overprinting, it is possible to make another black swatch as only the default black (has square brackets around it e.g. [Black]) will overprint by default. e.g.

and so that it can be easily identified amongst all the other swatches which may be in the palette, how about an appropriate name such as “Knockout Black” for example?

Among printers, there is debate about what constitutes an ideal “rich black”. Some argue that it is 60% Cyan and 100% Black; others argue various percentages of Cyan, Magenta, Yellow and 100% Black; but for me the values 30% Cyan 30% Magenta 30% Yellow 100% Black has worked for me for years.

The following picture demonstrates various fills in an InDesign file.

The next picture illustrates what happens once the various fills are printed.

In this example, it is clear to see that “White Overprint” has simply disappeared. Beneath the Black Overprint, it is still possible to see the headlights of the traffic trails of the photograph underneath. While Registration does look almost like a super black, what can’t be simulated on-screen is the effect that solid registration has on paper, over-saturating it and making it distort. Other reasons not to use Registration Colour as a fill can be found in the Registration Colour post.

Considerations should also be made when using Blacks with Metallic inks, as Metallic inks are opaque and block out the inks beneath them, unlike normal inks which add to the colours beneath them. See the Metallic Inks post for more information.

Controlling black overprints is often best left in the hands of a prepress operator, but I do believe that forewarned is forearmed.