Black is NEVER just black. There’s rich black, cool black, warm black, plain black – heck there’s even a “designer’s” black. Just as the hue of your favorite black t-shirt changes over time through numerous washes, it is true that each of the aforementioned blacks also change ever so slightly when viewed on-screen and in print. It’s important to consider these differences when you’re designing a printed piece to ensure that you will achieve the proper saturation you are after.
As you can see above, the difference between a “plain” black and a rich black can affect the density of ink that will fall in the desired black areas of the printed layout. Using different black settings will help to enhance your design and allow you a spectrum of black to use for different effects. A plain black is typically best used when printing text. If you have a large area that you wish to be a solid black, it is best to use a rich black (with the values C:60, M:40, Y:40 and K:100) so that you achieve a high density of ink, but aren’t over-saturating the sheet with 100% of each individual ink. Another reason to use rich black for small areas of black is to avoid trapping issues. Rich black is often used for text printed over images or a colored background to avoid any slight mis-registration between printing plates that would produce a white or colored halo around the text, making it more difficult to read.
Other blacks you may use include a “cool” black that has a slightly blue hue, or a “warm” black that has a slightly reddish hue. Registration black is used only for registration and printer’s marks and should NEVER be used when composing a piece for production. Why, you might ask? Having cyan, magenta, and yellow print all at 100% in addition to the 100% black will leave the press sheet drenched with ink. Depending on the paper used, this could result in the paper falling apart due to saturation, and a longer turn time due to the additional time needed to completely dry the sheet before finishing. Not to mention you may also experience chemical ghosting, where the image area transfers from the front of one sheet to the back of another sheet in the delivery unit.
In the electronic world, RGB uses values R:0, G:0, B:0 where no light is emitted from any of the three channels. In Photoshop, if you use the “Fill with Black” command, the defined black is actually the registration black (C:100, M:100, Y:100, K:100), but will still appear to be the same as the pure RGB black. While the image you are working with may appear to have a consistent black area on-screen, when the piece is actually printed there will be an immense difference in your black and the rich black Photoshop used in the fill areas. (See the above plain and rich black comparisons for an example)
It is important to remember this when dropping any solid black background logos in a JPEG or TIF format on to a solid black background in the artwork. Ensure that the values match by using the eye-dropper tool, or if possible, utilize the vector (EPS, AI) versions of the logo instead and drop it on top of the desired black values.
Before printing your next piece with a lot of black coverage, make sure you consult with your print provider to double-check their guidelines for a high quality black print.