Every designer will tell you that designing for print is a whole different thing. I go a bit further and say that it is practically a different career. There are a lot of tricks and details that need to be learnt, otherwise we expose ourselves to end up with hundreds of unusable leaflets lying on our desk, or with a very upset client screaming on our phone.
When printing artwork that has black in it, it is important to know that there are certain differences between what you see on your screen and what will come out of the printer.
CMYK vs RGB
As I am sure you already know, when you design for Print, you will have to use the four colour CMYK process. This stands for Cyan, Magenta, Yellow and blacK, whilst RGB is Red, Green, Blue. Most of the tutorials that can be found on the web in this regard talk about Photoshop settings, but since I am an Illustrator fanatic (I strongly believe that Photoshop is for photo editing and drawing and Illustrator for designing), I will explain it in Illustrator.
The first thing is always creating a new document. If the design is for web, use the Web Profile, select the size of your artboard (or change it later, it is not important), and it will go to RGB automatically, with a screen resolution of 72 ppi, which is enough to be displayed on the screen correctly. If you increase the resolution, you will get bigger images in terms of size, but on the screen the maximum resolution will be 72 ppi so you will just be adding compression to your files or making them bigger unnecessarily, and as we know, if you work on web, size matters.
On the other hand, if you will design something that needs to be printed, get started with the Print profile, and you will get CMYK as your Colour Mode and a resolution of 300 ppi, which is the minimum needed to get a good quality printing.
The default black in Illustrator when working on a RGB canvas will be R=0 G=0 B=0 (because in RGB, being an additive colour model, black is the absence of light), but if you translate the same black to CMYK in your color tab you won't get a pure black.
So, if you are working for your Print project from a RGB file, you might encounter issues later. Let's say, for example, that you are working in your RGB file, with your default black in RGB 0/0/0. And someone send you the art to be placed on a black background, but with the a 0/0/0/100 black on it. If you print this, you will be able to see the colour difference. If you are very lucky it might look as it was done on purpose, but believe me, most of the times, it looks clearly as a mistake.
How to avoid this issue?
It is quite simple actually. All you need to do is be aware of the different blacks that are involved in the game. We already discussed the RGB black, let's talk about CMYK.
CMYK is a substractive colour model, so you can get black adding colours to the mix. Here you have two ways of obtaining black when printing:
One is with only black ink at 100%, and the other one is with all the inks at 100%. There is no right or wrong here, so the use of one or another will mostly depend on what will be done with the artwork. (i.e. Newspaper ads will probably have different requirements than regular printers). But one thing is certain: the first option (only K=100%) is not as rich as the second.
So, if you drag the colour to the corner, you will get a richer black:
As you can see, the black obtained in this way is not 100% all the colours. In this case, the addition of the inks will amount to a 300% TIC (Total Ink Coverage) which is obtained by adding up the values of each ink. The ideal value for this varies from one designer to another, but most people recommend that the highest value should be around 250%, so C40 M30 Y30 K100 is a rich and safe black to use. You are using less ink in this way, and it should dry faster (although this is probably not our problem!).
For example, Jim Dittmer, who has worked in this area for many years, explains:
"The "blackest black" available depends entirely on what kind of printing process is being used. While it is true that one can get a deeper black than 100%K, the actual formula depends on what the allowable DMax for the printing press is. Assuming that the press house conforms to one of the common standards, the CMYK formula might be:
95,85,85,85 For a sheetfed press with a coated stock
75,68,67,90 For a Web press (SWOP standard) with a coated stock
55,45,48,69 For a Newspaper
These are just a few of the hundreds… maybe thousands… of possible press situations. And, of course, the quality and type of paper makes a huge difference also. Best to check with your printer for the specific press/paper combination.
But this doesn't really answer the question because typically someone looking to make the deepest, richest black is talking about a solid tint- often with type being knocked out of it. There are at least 2 issues to take into account here. First is maximum ink coverage, and second is the integrity of the type.
Typically, a Black flat tint (a background, for example) will be something like this:
These formulas provide a strong, rich black. Note that all use 100% black and work for almost any printing situation. There's a reason for that and it relates to the second issue…
Type integrity. In order to have sharp, well defined type, you need the primary background color to be solid. In this case the black. A 90% black will result in rough looking type. This effect is exacerbated if the type is trapped (as it should be). With a solid, 100% black, the type is sharp and clear… especially when trapped!
The reason we don't use even higher percentages in the CMY has to do with ease of printing. Large expanses of very heavy ink coverage is problematic during printing. It can smear, bubble, and take too long to dry.
So, use 60,40,40,100 for those Black backgrounds!"