Not all black colors are created equal…
If they look equal, like the image below…
…then you need to go to View > Proof Colors in InDesign/Photoshop/Illustrator to witness the true horror that will be your final printed black.
The difference between these previews is that black, as viewed on your screen with light, has a much richer color range than a commercial printer can produce using ink. That is, the Red-Green-Blue (RGB) range is much wider than the Cyan-Yellow-Magenta-Black (CMYK) range.
Here’s the deal, standard black, as in a black that has the CMYK value of 0-0-0-100 is a pretty dull black – it’s basically a washed out dark grey.
If you want your blacks to have some chutzpah, you need to dial in some CMY colors. This will give you a rich black, and while there is no standard rule for what values constitute a rich black. The main thing to remember with rich blacks is that your mix should always add up to less than 260% coverage or whatever your printer specifies as their maximum ink coverage for the material your job will be printed on. Too much ink results in "bronzing" -- a bronze sheen created by a layer of ink that cannot be absorbed by the substrate, so it just sits on top and is also almost impossible to dry completely, so you'll add time to the job.
Here's an instance where this subject will be very important: If you have a photograph with a black background and you place it on a cmyk 0-0-0-100 background it might look OK on your screen, but when printed it will look really bad. This is because photos are RGB color mode and when black is converted to CMYK will be a rich black and darker than your 0-0-0-100 dull black background. We recommend converting the photo to CMYK and then using your color picker to select the background color from the edge of the image for your background color. In most cases, this will do the trick.
Types of Blacks
Registration is 100% of everything: CMYK (100,100,100,100) plus any spot color plates. Registration marks are the only place Registration swatch is used, but they are in the slug, not in your artwork. Your layout program does this for you automatically when you export to PDF and select the option to include registration marks.
This black contains only black in the output with no other colors in use. This black is best utilised for very thin lines (hairline - 0.25pt) and small text (6pt). Why? If you’re printing fine lines or very small text with a rich black, you will have a printer first laying down black, then going over that fine line or text again with cyan, then again with magenta and finally with yellow. Printers can vibrate quite a bit when printing and any slight misalignment that is caused by that vibration will make the colours not print exactly on top of one another. This is what those registration marks are used for when setting up a document for print – they tell the printer if any of the plates are misaligned.
(Below diagram has been enlarged to show detail.)
So the best policy for very thin lines and small text is to just use a standard 0-0-0-100 black, and your work will come out crisp.
A rich black will include colors from the other 3 plates. There’s no set formula for this, but a good one to use is 50-50-50-100. Best practice would be to contact your commercial printer and ask them what mix they prefer you use for a rich black, and they may come back with a slightly less saturated black like 20-20-20-100. Bearing in mind how porous your paper is will also factor into your decision making for what mix of black you should use. The more porous the paper, the less ink you should use to avoid the ink bleeding into the paper.
This is slightly cooler in tone, but it has a really nice rich quality to it. It will be a mix of 70-50-30-100, for a total of 250% ink coverage with a cooler tint.
This black has more yellow in it and will have equal amounts of cyan and magenta with more yellow, for instance, 40-40-60-100, is a nice warm black tone.
This is a great choice for a strong black. Add equal parts magenta and yellow with elevated cyan and you got yourself a really nice looking cool rich black. 60-40-40-100 works well.
If you’re not sure what blacks you have in your document, use the color picker to determine how much ink are in the dark spots of your document.