Re: (Gum) Tonal scale

From: Katharine Thayer <kthayer@pacifier.com>
Subject: Re: (Gum) Tonal scale
Date: Thu, 01 Dec 2005 19:54:30 -0800

> My point was simply that for gum, tonal scale cannot be read directly
> from density of reaction products, because unlike silver, for gum the
> reaction products are separate from the material that produces the
> tonal scale. So you can't say for gum, as you might for silver or some
> other processes, that x amount of whatever-compound-results-from-
> exposure, will result in x tone on an absolute scale, or that the
> maximum tonal scale that can be produced by GUM in one printing will be
> around x units on an absolute tonal scale, as a result of the minimum
> and maximum amount of the compound that can be produced in a printing.

I don't know why you have to make gum so special in this regard. The
reaction product of exposing silver-gelatin paper is not the
constituent of optical density in the finished print. Furthermore, the
amount (gram per square meter) of developed metallic silver does not
uniquely determine the optical density of the image. 0.5 gram per sq
meter of developed metallic silver can have light gray or dense black.
Received on Thu Dec 1 22:17:56 2005