From: Judy Seigel (jseigel@panix.com)
Date: 07/07/03-01:22:10 PM Z
On Sat, 5 Jul 2003, Sandy King wrote:
>
> The point here is that my reference was carbon printing, not gum,
> though I believe many of the same principles apply, at least in so
> far as hardening and tanning of the colloid is concerned. Clearly the
> actual theory of how gum printing works is very different from carbon
> so no direct correlation is possible. However, for carbon printing
> the answer to your question is yes, the number of steps you can get
> on a print is more a question of contrast than exposure, assuming
> that you have at least one or two maximum blacks (or reds, blues,
> etc.). Beyond that point increasing exposure will not increase the
> exposure scale of the process.
Here gum is very different from carbon. Firstly, there is no "correct"
exposure for gum, as I gather there is for carbon. There's always the
factor of development.... length and type.
And you can definitely increase scale by increasing exposure --probably.
That is, if you expose more and develop more (longer and/or harder) you
have a good chance of getting a longer scale, especially with pigment rich
mix. True, the top tones may melt away at the same rate that the bottom
tones unblock. But sometimes they don't -- hence longer scale with longer
development.
I went into this at some length (& as I recall showed test strips) in P-F
#6 "Serious One-Coat Gum Printing"... Anyway, in continuous tone gum
printing, neither range nor exposure nor development is absolute, but
adjustable & flexible. Which may be why some expert photographers find gum
daunting... they've been taught to find the "best" set point for
everything. This is rarely possible for gum -- where a long bath can cure
almost anything except UNDERexposure. (Digital negs probably have less
latitude, but I haven't tested them on that yet.)
I'll add however that "range" matters more for one coat gum... for
multiple gum you can get added steps with another coat.
J.
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