The current state of home based emulsion making seems to be able to fairly easily get to ISO speeds as fast as 40 or maybe 50. Some have reported speeds up to 80 and even 100. My current emulsion brew is about 40. This got me to wondering: in today's measurements how did commercial films of the 1920's, 30's and 40's or even earlier compare? I recall hearing that film speed at the time was rated more conservatively than today. I'm specifically interested in black and white films.

My Kodak Tourist folder that I believe my father purchased new in 1947 has an exposure guide on the back listing three Kodak b/w films of the day: Super-XX, Plus-X and Verichrome. (Non-say PAN so I do not know if they were panchromatic films or not.) Going by the "Sunny 16" rule for an average subject in bright daylight, I would guess the speeds of these films as follows:

Super-XX 50 (1/50th @ f/16)
Plus-X 25 (1/25th @ f/16)
Verichrome 25

(Kodacolor is also listed and I would put that at 25 as well.) Does anyone have any data on other films?

Also, do we have any ideas about the manufacturing process of these b/w films? Were they SRAD's or made by other processes?

-- Jason