This is a quickie to write, but if you love the subject, it will be a very long and interesting dive.
Here below are the links to the most exhaustive series of articles I have ever found on the old "Ben Day" coloring technique used in comic strips and comic books for nearly seven decades.
It concentrates mostly on the birth of the technique and old material, but it is well researched and documented.
I have a particular fondness for the old "dots".
Kudos to the blog, Legion of Andy and its author Guy Lawley
- Part 1 — Roy Lichtenstein — the man who didn’t paint Ben Day dots
- Part 2 — Halftone dots, Polke dots, more Roy
- Part 3 — CMYK / Four-colour comic book dots vs. RGB dots on screens
- Part 4 — Pre-history, origins — Ben Day in the 19th century
- Part 5 — Ben Day in lithography
- Part 5.5 — French comic strips of the 1880s. Coloured by relief aquatint.
- Part 5.75 — A lithographic protocomic (?) from 1885
- Part 6 — Ben Day meets the Sunday Comics in the 1890s
- Part 6.1 — Tarzan and the Ben Day Dots—secrets of 1930s comic strip colour
- Part 6.2 — Fun With (Mis-)Registration—when colour printing plates don’t line up
- Part 7 — The Birth of the Comic Book
- Part 8 — 1930s to 1950s - The golden age of comics
