Re: (Gum) Tonal scale

>>> Ender100@aol.com 12/02/05 12:27 AM >>>
>>Hi Joe,

To me the exposure scale is the number of differentiated steps that
print
with a paper/emulsion when exposed through a standardized step tablet.<<

Makes sense to me as well. The negative prints out a certain finite
number of differentiated steps onto the emulsion/substrate. If exposure
is optimized and steps 1-15 are differentiated, the material has a
15-step exposure scale. If overexposed and some shadow steps are
blocked, the printed steps may advance up the wedge so that perhaps only
steps 3-17 are different, but the exposure scale stays the same, a
15-step range.

I think the confusion comes in when someone tries to say the negative
density range should be X for a certain process. (If you compare James,
Schaeffer, and Crawford for example, you'll see they state several
different negative density ranges as appropriate for a given process
like salted paper.) The problem is one author is taking the net
negative density range to be equivalent to the exposure scale, another
might be talking about textured zones from II to VIII, amother using III
to VII and calling that the negative density range, and still another
might be looking at 0.10 over fbf through threshold white and using the
same term for that. And, for example, I simply can't figure out what a
tone "just slightly lighter than maximum" means. Just how much lighter
in tone is "slightly lighter"? You have to either have a visual
referent or some measurement to make sense out of such statements.

>>You could
have a lot of steps and still not have that high of print density.<<

Agreed. The maximum density of single gum layer just is not going to be
very high even though many steps may print out. To get greater density
you have to either sacrifice some range in the highlights by using a lot
of pigment and a relatively brief exposure with the resultant posterized
look, or build up multiple thin detailed layers using lower pigment
ratios and extended exposures.

And, several layers of gamboge printed optimally is not going to have
the same density as several layers of ivory black printed optimally due
to the differences in tinting strength, OTBE. One of my favorite
transparent colors is cobalt violet but it is very difficult to print
anything other than a tint of this pigment even with multiple layers.
OTOH, something like an opaque Indian Red is going to print much
stronger in a single exposure. All of these pigments are going to have
different exposure scales, especially when combined with other variables
such as paper texture, sensitizer, sizing, gum to dichromate ratios,
etc.

For doing something like 3- or 4-color gum, I think it would be great if
such exposure scales could be quantified for each gum layer assuming the
goal was semi-accurate color and a specific set of tricolor pigments and
a black kicker were always used along with an inflexible processing
schedule and auto-development. For monochrome work or interpretive
color, I suspect the joys of gum printing are related to a more
freeform, sensible, and qualitative approach with brush in-hand and a
"let's see what happens" attitude.

Joe
Received on Fri Dec 2 00:51:12 2005