Re: (Gum) Tonal scale

On Fri, 2 Dec 2005, Joe Smigiel wrote:
> No big surprises here except the curious response of the Bone Black
> pigment test (bottom middle). Take a look at the circles around the
> numbers and step areas 14 and higher. There is definite pigment stain
> in those areas which should be paper white. It is as if there is a sort
> of pigment stain solarization effect happening. Steps are
> differentiated from about step 6 through step 13 and then the steps
> print darker due to pigment stain. I speculating that a very small
> amount of exposure has caused steps 12 & 13 to print almost paper white.
> I'm thinking the slightly exposed gum there has reduced pigment
> staining which perhaps has occurred during wet processing. IOW, as the
> prints autodevelop in water, this particular pigment is released from
> all areas of the print to some degree and it muddies the water. Where
> an exposure hasn't had any effect at all, the pigment migrates to the
> unprotected paper and stains it. This is only happening under the gum
> though. Areas outside the coating remain unstained and protected by the
> gelatin size. Somehow the emulsion has caused the areas beneath to
> stain disproportionately, perhaps by adversely affecting the sizing or
> somehow interacting with it and weakening it. Has anyone else seen this
> before or have an alternate theory of why it has occurred?

I showed same or similar effect in Post-Factory #3, p. 37, "Funny Gum
Trick/ Direct Reversal,'solarized.'" Also showed the white lines around
the numbers on the 21-step. I think your hunches about the reversal where
there's been *some* exposure, but not enough to tint the paper are on the
mark. I quoted Mike Ware, who theorized that "The less viscous the
emulsion...the more it soaks into the paper, hence the more stain. The
steps *directly* above the 'legitimate' tones have had enough exposure to
make them slightly viscous -- not enough to leave tone in the print, but
enough to forestall stain..."

Etc. I drove the effect to its maximum with a reversal print done with an
extremely dense negative, theorizing that "detail in those regions should
print in reverse." And it did. Only some pigments did this, however. Mine
was a Winsor Newton ultramarine. (Rowney ultramarine wouldn't.) I'd expect
that black would be even better.

J.

>
>
> Here are the 5 test conditions and the results:
>
> 1) Upper left: Saturated potassium dichromate image only/ 17 steps
> differentiated/ very slight dichromate stain
>
> 2) Upper right: No pigment/2 parts gum arabic/1 part saturated
> potassium dichromate/ 12 steps differentiated/ very slight dichromate
> stain
>
> 3) Bottom left: 1 gm cobalt violet powdered pigment/10ml gum arabic/5ml
> saturated potassium dichromate/ 6 steps differentiated/ very slight
> dichromate stain/ no pigment stain
>
> 4) Bottom middle: 1 gm bone black powdered pigment/10ml gum arabic/5ml
> saturated potassium dichromate/ 7 steps differentiated/ pigment stain
>
> 5) Bottom right: 1 gm lampblack powdered pigment/10ml gum arabic/5ml
> saturated potassium dichromate/ 7 steps slightly differentiated/lots of
> pigment staining and flaking
>
> I'll be running a few more tests with different pigments in the next
> several days. After I have them all scanned, I'll treat them in a
> potassium metabisulfite solution to see if I can totally get rid of the
> dichromate images and dichromate staining.
>
>
> Joe
>
>
Received on Sat Dec 3 01:56:56 2005