Clyde, You're asking an excellent question. However to answer it exactly
would be, aside from hubris, a lie. Because each paper/emulsion/developer
combination has a different profile. Not to mention your aesthetics.
You may not be able to afford a densitometer, but you can get a Stouffer
21-step for $5.50, or $2.70 each in large quantities. Get a bunch. (I
posted address info this week.) Now print this little piece of film (1/2
inch by about 6 inches) on a little piece of the paper you plan to use. Do
everything as you would for a photograph, except you need only a couple of
drops of everything, & small pieces of paper, so the cost of false steps is
negligible.
When the print of the 21-step is good and dry examine the steps. When
you've made one with nice creamy highlights and good rich darks, note the
numbers of the steps -- where the dark separation begins, where the
highlights start to disappear or veil.
That range is the range negative you want. Say rich shadow with separation
starts at #4, highlights vanish at #14, that's 10 steps. On the 21-step
in question, each step is a half a stop, so that means you want a 5 stop
negative. Match your negative to this range with the hole-punched cards
on a light table as I described a day or two ago.
Of course your particular negative doesn't have to start & end at exactly
those steps, if the *number* of steps is the same. You may also want to
experiment with contrast controls in the print and/or different papers
and/or different emulsion application techniques to modify this range.
Incidentally, once you have the "profile" of a paper/emulsion combination
on the print of a 21-step, you no longer need to do test prints --
assuming you haven't changed a variable. In other words, "read" the
negative via the 21-step through the punched holes, and adjust your
exposure time accordingly. This is actually better than a test print
under the negative because you don't know the final tone for at least a
day. Your little guide print has already aged. Besides which, sometimes a
print takes an hour or more to make -- a gum print can take a day to
soak. That's no fun.
Judy