Re: tonal inversion and pigment loads

From: Katharine Thayer ^lt;kthayer@pacifier.com>
Date: 01/30/06-10:24:55 AM Z
Message-id: <4FD059B1-F919-4C73-B5AE-A6440EF7ADFB@pacifier.com>

On Jan 30, 2006, at 5:16 AM, Jack Brubaker wrote:

>
>
>
>> From: Tom Sobota
>>
>> After half an hour of inmersion in water facing down, these
>> large and loose grains
>> should have gone to the bottom of the tray. But somehow, they didn't.
>>
>
> I am only making wild guesses here but static charge is stronger in
> larger
> particles. So perhaps your observation helps point in that direction.
>
> Katherine wrote:
>
> why did the numbers wash off only in steps
> 17 through 21? The numbers should consist of hardened gum of the
> same density from steps 1 through 21. The stain is the same tone
> from steps 10 to 21, meaning there's no more hardened gum underneath
> to act as a resist against the stain, as there is in steps 5 through
> 8, and so the unhardened gum should dissolve equally and completely
> from all the steps from 10 to 21. Your explanation above is
> intriguing, but I don't think it takes these facts into account.
>
> My response:
>
> If static charge is working in this there is no reason to expect it
> to act
> "photographically". It may be a contrary force that only comes into
> play
> under certain conditions. I wonder if the condition of the numbers
> high in
> the scale are that condition but don't claim to understand.
>
> It does happen in some cases when powder coating that a charge is
> built up
> in an area that will attract powder to that area but repel powder
> in a small
> area within that area. It doesn't make sense when it happens, but
> it does. I
> don't see how a charge could be being created in the gum, but...
>
> If it's not static charge holding that loose powder that both Tom and
> Katherine have observed what is it? I Don't know.

Jack,

I like your idea that it's probably some sort of static charge that's
holding the loose pigment to the substrate in areas where there's no
hardened gum, and where the pigment hasn't penetrated fibers to
create an indelible stain, and I think your insight about that is a
great contribution. But that's not the case with the numbers, which
should consist of hardened gum. Where the numbers are visible, they
consist of a full layer of hardened gum containing a full complement
of pigment; where the numbers are not visible, or appear light
against a darker background of stain, they consist of a thin layer of
hardened gum that's left after the bulk of the emulsion has flaked
off. What's odd is that in a condition that creates stain, the
higher numbers seem to be inclined to flake off, even though all the
numbers should print to the same level of hardness. I don't
understand what's going on with that, but I think it's a different
issue than loose pigment sticking to the substrate.

Katharine
Received on Mon Jan 30 10:25:20 2006

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