Re: Tonal inversion (was (Gum) Tonal scale)

Tom, your comment that you had this problem with x-ray film (which has high
silver content I believe) reminds me of my experience with the gum tone in
the whitest part of the image. I found that when this happened If I changed
to a less dense negative the effect went away. I suspect from my experience
that the excess density (way beyond the gum's ability to print) was causing
the reversal by heat exposure of the gum from the dense black in the neg.
heating up during the exposure.

Jack

> From: Tom Sobota <tsobota@teleline.es>
> Reply-To: alt-photo-process-l@sask.usask.ca
> Date: Sat, 03 Dec 2005 11:36:00 +0100
> To: alt-photo-process-l@sask.usask.ca
> Subject: Re: Tonal inversion (was (Gum) Tonal scale)
>
> Joe,
>
> This 'solarization' happens, I have seen it mostly with blacks under
> high density areas of the negative. But sometimes with other colors too.
>
> Years back I was using x-ray film, which was double coated and had
> a very high D-Max and this value inversion happened frequently.
>
> It was driving me crazy so I stopped using x-ray film which was
> a very good idea...
>
> Have a look at this test strip, printed with lampblack (0.03g in 2cc
> gum solution + 2cc Amm.Dichromate 30%, paper twice sized
> with gelatine)
> http://usuarios.arsystel.com/tksobota/Lampblack_strip.jpg
>
> I have exaggerated somewhat the contrast so the effect is
> easier to see. In the original, all the steps of the three strips
> are distinctly visible and separated.
>
> I have no explanation for this effect, but I think that it has
> been mentioned on this list some time back.
>
> Your idea about the muddied water and pigment migrating
> could be perhaps tested developing a test strip under slowly
> running water, instead of the usual 'stand' developing.
>
> Tom
>
> At 02:42 03/12/2005, you 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?
>> Joe
>
>
>
>
Received on Sat Dec 3 13:34:16 2005