The 1938 Kodak chemistry book includes the formula D-61.
That looked sort of funny so I looked at a 1950s edition of
"Processing and Chemicals" the booklet included in the "Kodak
Reference Handbook" and found the formula was now D-61a. So, what
is the difference. Turns out that D-61 has 30 grams/liter of
sodium sulfite while D-61a has 50 grams/liter. They are also
described differently; D-61 is a developer for high speed machine
development of roll films and D-61a is a general purpose
developer for film. Now, there are two Kodalk developers; DK-50
and DK-60 which vary in the amount of Kodalk. DK-60 is described
as a photofinishing developer while DK-50 is a general purpose
developer. Of course the difference is in the time it takes them
to reach a given contrast. I am not sure what the difference in
performance of the two D-61 formulas are but evidently the "a"
version was more satisfactory because the original is not
reprinted in later references.
Kodak had lots of formulas some of which differed by very
little.
--
Richard Knoppow
dickburk@xxxxxxxxxxxxx
WB6KBL
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