I was researching various toners and stumbled upon an interesting article from camera magazine in the early 1990s. Then I realized this was an invaluable resource for anyone who wants to do research on early photographic techniques, fomulas, and even early portraiture techniques. The magazine has interesting articles and several illustrative images in halftone reproductions. Overall a fun read for the photography buff.
I found volume 13 but there are many others.

Google Books https://books.google.com/books?id=Vz...page&q&f=false