Solid blacks in printing are hard to obtain. One way to achieve success is to use opaque ink in a silkscreen printing process. This will work on most any surface, such as paper, wood or cloth. Or if you are using 4-color process, strip in a screen of 40% cyan behind the black. Consider using a low LPI and commit yourself to losing detail in your design. This is a good possibility if you’re going for a black background on a portion of your printed piece. Try using varnish to process black ink or overcoat with varnish to gain a gloss. This will help reflect light and give you a deeper black.