Mezzotints are a method of converting black and white continuous tone images without using hatching, cross-hatching, or stipple. To reduce file size, but add coarseness, a mezzotint can be converted to a bitmap image (in Photoshop or GIMP and probably other image processors.) A bitmap image consists of only black and clear pixels. This makes it possible to do some interesting stuff as overlays in page layout programs or Photoshop.
To demonstrate this, I took a self-portrait photo (yes, that’s me 10-years ago. My beard is white now.) And put it through two processes. One is making a mezzotint from
the black plate (K channel) and the other a mezzotint produced from a grayscale conversion (#2.)
Both of these “bitmap layers” are placed over a CMYK image with the “K channel erased” or as I call it “CMYN.” N meaning none. These make for an interesting aging effect but still colorized (not a duotone or Sepia tone.)
Now you can take perfectly good, crisp photos and make them look “old and ugly.” Below are the finals: