Re: (Gum) Tonal scale

On Dec 3, 2005, at 12:44 PM, Katharine Thayer wrote:

> Joe, you've illustrated my point about how pigment and pigment
> concentration can affect tonal scale very nicely, thanks.
>
> I'm not sure how the dichromate stains relate,

Unless, like some others, you're still missing my point. Just in case
the dichromate stains and the pigment swatches on your page were
intended to be read together as disagreement with a misreading of my
argument, in other words if like Judy you thought I was saying that
dichromated gum without pigment would print the same tonal scale as gum
with pigment, which makes no sense at all, let me say for the 10th time
that I've never said that, in fact I've said rather the opposite.

I'll add, on the chance that it might be useful to someone who is still
struggling with the concept, and in case my previous comments on
dichromate stain weren't explicit enough, that dichromate stain is also
an indirect, not a direct, way to infer density of reaction product in
unpigmented gum. Unlike pigment, dichromate stain is actually a
response to exposure, so it's closer, but like pigment, it's not the
reaction product.

My whole point was that you can't read density of reaction product from
tone, except in an indirect and relative way, since unlike some other
processes, what you're looking at when you're looking at tone is not
the reaction product itself. The reaction product is essentially
invisible, and the tone is expressed by pigment, which isn't a reaction
product.

If you hold a print made from unstained unpigmented gum at an angle to
the light, you can see the image in all its detail, but you can't
judge the different densities of crosslinked gum, because they are all
colorless. The crosslinked gum has different densities, but it has no
tonal scale. That is the entire point I was trying to make. The tonal
scale is expressed by pigment, and since I keep saying that every
pigment/concentration will produce a different tonal scale, it's
obvious I mean that tonal scale (pigment) and density of crosslinked
gum must be related in some way; it's just that we don't know enough
about that relationship to be able to graph it and be able to read
density of crosslinked gum directly from tone.

  Of course there must be a relationship between the densities of the
reaction product and tonal scale, since the density of the pigment is
greater where there is more exposure and therefore presumably more
density of crosslinked gum, and also because, as I and everyone else
keep saying, different pigments/concentrations produce different tonal
scales. But my point is that we don't know what that relationship is.
And since we don't know what that function is, and since knowing the
relationship is not essential to understanding how to print gum, it
makes a whole lot more sense to just look at the relationship between
exposure and tone and not worry about how either might precisely relate
(in a quantifiable sense) to density of crosslinked gum. That's the
whole point. I said that it was a very narrow point and people have
been overinterpreting it, but even after I've said that several times,
people keep on overinterpreting it.

Katharine
Received on Mon Dec 5 23:46:06 2005