I'm working on a full color piece in Illustrator which has a few large black and grey areas.
I'd like the black to be a rich black. I was thinking c30 m30 y30 k100. What is the best ways to match my gray areas?
Talk to the production house and ask them what rich black they prefer. There is no single rich black every print provider uses. Each print provider has their own formula for a rich black. And, in many cases, the print provider may want simply 100% K and they will adjust the black to match their own environment. Therefore, the best option is to ask the print provider how they like rich blacks handled.
There are a couple ways to handle tints of the rich black.
The easiest .... make it a Global color. Double click the swatch in the Swatches Panel and tick the "Global" option.
More cumbersome.... hold down the Command/Ctrl key when you adjust color sliders. This will cause all 4 sliders to move in unison.
When doing rich black you need to keep in mind it will have a tint when used as gray or as a gradient.
You might want to use this to your advantage either by using a mix of rich black that will look neutral in its gray shade or by using one that has more Cyan, Magenta or Yellow if you actually want to create a colored gray.
A "safe" way to mix your black is by keeping the yellow and magenta a bit lower than the cyan; this way your black will look more gray metallic than brown when used with transparency, gradients or grays.
Cyan = 30 Magenta = 20 Yellow = 20 Black = 100
Examples of different rich black and their gradient/gray:
What about asking the printer?
Yes, that's an idea, when it's possible to contact the printer. Sometimes it's not an option. But if you can contact the printer, he will SUGGEST you a black that prints well but that's in NO WAY the only rich black you can use. The one they usually suggest is one that prints with consistency on large areas (see second point.) There's even some cases where you should use a C1-M1-Y1-K100 for example and even though it's barely a rich black, it still accomplishes what it supposed to do. You can freely create any kind of rich black as long they have an acceptable density and give you the effect on gray/gradient you want. That's why it's good to understand how colors work.
Another point is you should choose your black recipe carefully. If your layout contains a lot of blue for example, you should try to use a rich black that is very neutral or uses more cyan than magenta and yellow; otherwise that black will look brownish or warm compared to the rest of your design.
In all case, your ink density should not be above 300; that means when you add the Cyan, Magenta, Yellow and Black values together, the total should be kept below 300 ideally.
If you're doing a project for offset printing, you need to be very careful in your choice of fonts.
Sometimes the registration of the press is not perfect; this happens when the 4 plates of CYMK separations are not well aligned.
When this happens, using a white text on a black background could show the other separations within the white part of your letters.
For this reason, you might want to use a font that isn't too thin; the thinner the font, the more fuzzy the text will look. A normal/roman or bold font will already help save a bit of your design if that happens. At least the text will still be white and readable.
For the same reason, you need to also be careful with small text on white; when it's not necessary to use the rich black, simply use the normal 100% black only for small texts or very small graphics.
Simply create your swatches of colors when you start your design and use the same black color everywhere on your layouts. You don't need to make these swatches "spot", you can simply use them as "global" color.
Before you send your PDF files to the printer, verify if you did a good job. You can use the separation preview in Adobe Acrobat Pro and verify if all your black are 1) using the same rich black recipe and 2) that you don't have any big areas using a 100% black only.
You can do this by unchecking one by one each separation and adding them back in the preview. Usually it's easy to spot what needs to be fixed!
More details on rich black already answered here:
Trick to use a rich black instead of 100% black with overprint trapping or another way to choose your rich black to match a background color:
Contrast of different black in design
Avoiding issue with the difference in rich black when placing rasterized images in Illustrator or InDesign with vectors
Rich black used with gradients VS RGB black
If you know what ink coverage means in printing, then you would analyze the formula. There is a minimum to a maximum ink coverage:
Maximum Ink Coverage is based on a 240-260 % ink Coverage. If you take the rich black that is generated automatically in Photoshop, which is
C=75 M=68 Y=67 K=89 = 299% ink coverage. Your saturation is way pass the 240-260% ratio. Most print houses utilize a formula
C=60 M=40 Y=40 K=100 (240% ink Coverage) or
C=40 M=30 Y=30 K=100 (a bit less than average).
These formulas are best for rich black. Remember that the term
RGB is not utilized in Litho Printing. Therefore you cannot use
CMYK formulation on an
Coming from a print background I can tell you that the
CMYK for a rich black is
C=75 M=68 Y=67 K=89
This will give you the best black. If you are sending to an
RGB printer like any desktop
(yes they print
CMYK and have all those cool mid tone cartridges but they take
RGB images and have there own internal rip that converts it)
I would use
R=0 G=0 B=0 If you use process black or
C=100 M=100 Y=100 K=100 you will end up with a muddy brown on a
Also on grey the printer will always use all of the colors to print grey, it will never use only black ink. This is to retain detail in the grey areas. I would make sure that you are adding a little more cyan or magenta to make the greys cooler or warmer depending on the look you are after.