Re: (Gum) Tonal scale

Hi Joe,

Yes, if you continue to add exposure through a standardized step tablet
(stouffers), then you just move the same number of DIFFERENTIATED Steps up the
scale. This is helpful however for determining a proper Standard Exposure
Time, since once you get two or more of the darkest steps merged, you know how
much exposure is just enough to obtain printed DMax.

I think that the writings that suggest various negative densities for
different alt processes are just that—suggested starting points for various
processes, which would be very helpful when using in-camera negatives. With digital
  negatives, it is so easy to adjust the density of negatives by
modifying the color, that it is not such a great issue. However, knowing that an alt
process such as gum might take a negative with a density of around log 1.0
or 1.2 compared to salt prints, which might take a negative density of
around log 2.6 is helpful to know. When working with an alt process which
allows such contrast control, such as PT/PD, then a range of densities is
more informative. Knowing these ranges for different processes, or how to
adjust contrast with different processes, can also be helpful if you want to
make a negative and be able to use it with more than one process.

By definition, an alt process with a given exposure scale requires a
negative of a corresponding density range.

You've stated well the difference in print density that is a result of the
visual density of various pigments. Obviously, a yellow is not going to have
the same density as

I think your comments about getting good full color with gum are on target.
  The work that Chris Anderson has been doing with full color gum and
calibrating with the PDN system is very revealing and has given her what seems to be a
 very accurate reproduction of color—and each curve is different for each
color—with Yellow having the curve that varies the most from the others.

Best Wishes,
Mark Nelson

In a message dated 12/2/05 1:54:14 AM, jsmigiel@kvcc.edu writes:

> >>> 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.
>
Received on Sat Dec 3 12:57:38 2005