Re: son of a gum tonal inversion test

On Dec 7, 2005, at 7:50 PM, Dave Rose wrote:

>
> I've also seen the strange tonal reversal that you've experienced with
> Daniel Smith's Bone Black. I've experienced it using Sennelier's Mars
> Black
> and Black For Fresco (powder pigments) used at higher concentrations
> that
> cause background paper staining. It seems that minimal exposure (as
> seen on
> the higher points of the step wedge) will help clear certain pigments
> off
> the paper while non exposed areas are heavily stained. No idea what's
> causing it, but the effect disappears at lower, non-staining pigment
> concentrations.

Hi Everyone,

It's true I wasn't following the tonal inversion thing, but I always
read Dave's posts. So I read Dave's post, and got to thinking about
the example of this tonal inversion that I got on a step tablet using
burnt umber last week. It wasn't a mix that I had ever printed with,
because I usually use burnt umber as a red additive, adding it to black
to warm it perhaps, or with yellow added to make brown, but rarely by
itself, and when I do I use it by itself, I print it as a red, rather
than as a brown, so I don't tend to use it at full strength. But I
wanted to show someone what color burnt umber is, because we were
puzzling privately over a dry pigment he had bought which was
confusingly designated as Earth of Cassel, PBr7. I said it couldn't be
both; if it were Earth of Cassel, it would be NBr8, and if it were
PBr7, it was probably burnt umber. So I printed him a sample of burnt
umber to compare, and I added considerable extra paint to my usual mix,
to show it at full strength. I was trying to make it as dark as it
could be printed, say as a one-coat, but I was just guessing. The
step tablet did show this tonal inversion thing, and today I did some
test prints with that same mix, and it's definitely too pigmented and
does stain quite heavily. It may be that this tonal inversion on a
step tablet could become a quick test to see if your pigment will
stain, although I'm not sure it would work with all pigments.

Anyway today I took that same burnt umber mix and printed a picture
with it, and sure enough I got the same ("weird beard") inversion
effect that people have been describing and showing here. I tried it at
several exposures, and will scan these after they dry, if I have time
later. So now I've read back through the discussion to see what people
think about this. Others have already demonstrated that it's not heat
or exposure, with which I concur. I agree with Dave and others that
it is just plain old pigment stain, except that where there's been
some exposure, the formation of stain is restrained by the presence of
hardened colloid in the paper. A total inversion, where what should be
the darkest parts are the lightest parts and vice versa, seems to me to
be caused by the pigment load being too heavy and the coating sloughing
off the paper in development, leaving just enough hardened gum (or
hardened sizing, maybe) behind to keep the pigment from staining in
those areas, although it stains heavily in areas where there wasn't any
exposure.

This is rather annoying, because it means I have to rethink my theory
of pigment stain.My observations and experience had led me to believe
that pigment stain happens the minute the coating is brushed on the
paper. If it's going to stain, it's going to stain right then, and
there's nothing you can do about it from that point on, was my thinking
from what I'd seen before. But obviously, this set of observations
blows that out of the water.

What's interesting to me is what this effect might tell us about
top-down vs bottom-up vs something-in-between hardening. I'm not sure
just now what it does tell us, but I think it merits reflection and
study. My first thought is that it disconfirms top-down hardening,
because you've obviously got hardened colloid in the paper even when
the emulsion layer above wasn't hardened enough to stick to the
hardened colloid or the paper below. But I might need to think about
that some more. Anyway, now I think it's a whole fascinating thing,
though a few days ago I was so uninterested in it that I wasn't even
tempted to follow the discussion,
Katharine
Received on Sun Dec 11 14:49:25 2005