From: Sarah Van Keuren (svk@steuber.com)
Date: 01/02/01-09:43:40 PM Z
Thanks, Joe. I find your explanations helpful and in line with the little
bit that I know, or think I know, already ‹ such as the brown of vandyke and
P.O.P. coming from very finely divided silver, and the blacks of silver
gelatin coming from larger crystals, and blue/black tones (of Azo?)
reflecting from even bigger crystals. I like to have explanations for
phenomena like these even if I can't prove it like a chemist/physicist.
One aspect of vandyke that I've never had a pop-science explanation for is
how the dilute fixer reduces the silver nitrate to metallic silver. Can you
help me with that? If I don't respond it is because I'm going to be away and
without a laptop Jan. 4-19.
Sarah
> For what it is worth, heat is the first recorded method of toning all of the
> earlier processes. Herschel reported that a salt print when a hot iron was
> passed over the image showed a definite color shift. I do not know the
> chemical changes that occur during this process. But it would be safe to
> assume that heat drives out any humidity contained in the image, rearranging
> the image crystal molecules. The effective color of an image is directly
> related to the crystalline structure that forms the image. Bigger crystals
> reflect a different wavelength than small ones. Different metals have
> different sized crystals. The application of heat changes that surface
> structure forming the color changes. Color shifts due to chemical toners
> operate on a different level, but the underlying principle is the same. The
> crystals of silver are plated with another metal changing the size of the
> image forming crystals. This plating alters the way light is reflected or
> refracted off the image forming crystals.
>
> I am not a chemist/physicist, nor do I play on television.
>
> Joe
>
> ----- Original Message -----
> From: Sarah Van Keuren <svk@steuber.com>
> To: <alt-photo-process-l@sask.usask.ca>
> Sent: Monday, January 01, 2001 7:00 PM
> Subject: Re: Color of Vandyke Browns, was First Kallitype
>
>
>> Sandy, yes, I have found that if a vandyke print is flattened in a
> drymount
>> press with the image in direct contact with the hot metal, or if it is
>> ironed directly (without steam), the color change that you noted occurs. I
>> thought that it had to do with contact with metal but maybe humidity
> within
>> the paper is brought to the surface of the image and causes the image
> shift.
>>
>> Sarah Van Keuren
>>
>> > Just curious, though, in addition to the gray/black colors you sometimes
>> > have seen are, there other colors that one can get from Vandyke? I am
>> > curious because a while back I used the dry mount press to flatten a
>> > Vandyke print out and it changed the color from a light chocolate black
> to
>> > a very deep dark/black much more neutral in tone. When I put the print
> in
>> > the dry mount press it still had some humidity in it, though it was dry.
>> >
>> >
>> > Sandy King
>> >
>> >
>> >
>> >
>> >
>> >
>>
>
>
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