I prefer the double-negative technique. Just by coincidence, I stumbled upon my old copy of Kodak's
Copying and Duplicating book, about mid-80's vintage. There is a wealth of information in there, even
though some of the specialized films are no longer specifically available. You might hunt for a copy
of this publication in some used bookdealer search engine. But not much has changed per technique
since the 1920's. Helps to have a decent contact printing frame.