Re: Re: More and more observations

Dick wrote:

>I was rushing to get to the airport so to finish up:
>
>>To repeat an earlier observation, it is my opinion that even though
>>there is a print-out image its role as an absorber of actinic light
>>is very small in comparison to the role of the pigment. This is
>>different from chromate absorption. If this is not so I can find no
>>other reason to explain the different curves you see with POP
>>processes such as salted paper and albumen when compared to carbon.
>>The POP processes show a very long toe which in the print
>>translates into poor separation in the shadows, whereas the carbon
>>print shows a very straight line curve that gives excellent
>>separation in the shadows. If the print-out image in carbon were to
>>have a significant impact on exposure would this not logically
>>result in a long toe?
>
>Hmmm...
>
>I am not sure that what you describe is particular to POP processes.
>The ones you describe are silver based. Could it not be that
>carbon/dichromate is essentially different from silver or iron based
>processes?

I am talking here about the effect of self-masking on image
formation, and to the best of my understanding the results of
self-masking, which are a very long toe and compression of low and
mid-low shadow values, are typically seen in POP processes of all
types. You appear to have suggested that the print-out image that
results on exposure of sensitized dichromate, in the absence of
pigment, impedes further penetration of UV light. If so, in theory
the result from self-masking should be the same as in other POP
processes, regardless of whether the light sensitivity is silver,
iron or dichromated colloid processes. That is, the longer you expose
the image the less contrast it will have. I have not found that to be
the case in carbon, in fact the opposite appears to be true, at least
when dealing with exposures in the 15 minute to 4 hour range which is
about the limit of my experience.

>
>I think Carl Weese did some curves on Ziatype and found better
>shadow separation than withe conventional DPO platinum.

Carl may have made some visual comparisons of Ziatype with
conventional platinum (did you mean DOP, POP, or DPO?) and from those
comparison concluded as you suggest. However, I don't believe that he
has actually made sensitometric tests using a densitometer and
plotting the resulting readings. I may be wrong but from my
conversations with him a couple of years ago when he visited here in
SC I recall that he indicated that he was not using sensitometry in
this way in his work.

Sandy

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