There are two kinds of black ink made from colors: rich black and registration black. Both are made using a mixture of cyan, magenta and yellow inks.
Rich black uses cyan, yellow and magenta inks, but does not use 100 percent of any color. The percentage of each colored ink varies. There are circumstances in which it is better to use rich black instead of the pure black ink that is included in printers. In a method of printing called offset printing, pure black ink can look washed out or gray, so rich black is often used. In addition, there is a process called overprinting, where black is printed over other colors, and rich black does the best at blocking out other colors. Rich black also looks better when printing large blocks of black, and when printing large headlines in fonts that have very thick strokes. Rich black is also called black bump, Photoshop black, designer black and warm black.
Registration black is made of a mix of 100 percent of yellow, cyan and magenta ink, which can result in total ink coverage. This sometimes creates undesirable thick or raised areas due to the additional layers of ink. Registration black is used to print registration marks, crop marks and center marks that are used for image alignment.