Re: tonal inversion and pigment loads

Ahhh ... not so fast, Katherine :-)

I admit that at first I dismissed your idea of the pigment just laying
on top of the substrate without any gum to hold it. Since then, I have
seen this happen on paper, so I now changed my mind and agree that this
not only is possible but happens, at least with certain pigments.

But on the other hand, the images I have shown of my tests of gum on
glass show very clearly the presence of gum. The silvery sheen of gum is
clearly visible here
http://usuarios.arsystel.com/tksobota/Gum_on_glass_12.jpg for example.
Could you say that this is the color of plain lamp black on a black
glass? I don't think so.

I don't question your tests, since I have not seen them and under given
conditions everything seems possible at this point. In my case, the
layer of gum is very thin and rather fragile. But this doesn't mean that
there is no gum. You can see it by yourself and judge.

I do not pretend to understand how this happens, mind you. In general
terms it seems to be the same or a closely related effect as tone
inversion on paper. But since using glass without any substrate we have
taken the variable 'paper' out, we have, as perhaps you would say, one
less degree of freedom, which is great.

Tom Sobota
Madrid, Spain

Katharine Thayer wrote:
>
> On Jan 27, 2006, at 7:16 AM, Jack Brubaker wrote:
>
>> It is exciting that these issues are getting serious attention.
>> It is too
>> soon to rule out any possibilities.Tom's observation that the grains of
>> pigment are moving in a puddle make me wonder if it is possible that
>> static
>> electricity might be a factor.
>
> Well, static electricity may well be a factor in holding the pigment
> to the substrate; I'm certainly convinced that it was what held the
> inversion I made on glass, to the glass, and that might explain why
> pigment stain holds onto sized paper even though there's no hardened
> gum to hold it in place, which puzzled me. It was obvious that the
> inversion I got on glass (black letters where white, or clear in the
> case of glass, letters should be at the top of the Stouffer tablet)
> was constituted entirely of lamp black pigment, not hardened gum,
> because it wiped off easily with a fingertip or a tissue, whereas for
> me, hardened gum has to be scraped off glass with a sharp razor blade
> and sincere effort. That's the point at which I became completely
> comfortable saying that the inversion is just another kind of pigment
> stain, when I saw there wasn't anything there but pigment. And the
> fact that Tom has looked closely at his inversion and found it made of
> clumps of loose pigment, just provides more support for that comfort.
>
>
>> I apply powder (pigment in small grains of
>> plastic binder) to my metalwork via a static electric powder coating
>> process. It is amazing how little charge is needed to aggressively
>> hold the
>> powder in place on the metal substrate. The Xerox process perfected the
>> photocopy use of light and static charge. Perhaps there is some weak
>> static
>> charge generated in the environment under the darker areas of the
>> negative.
>> That the grains are loose in a puddle doesn't sound like a hardened
>> gum from
>> heat having crosslinked the gum. But, perhaps some combination of
>> heat and
>> other factors causes the beginning of a weak crosslink coupled with a
>> static
>> charge. The above are wild guesses for the sake of continuing the
>> dialog.
>
> Naw, there's no crosslinking here, just plain old pigment stain. IMO.
> Katharine
>
Received on Fri Jan 27 16:30:34 2006