Re: Rethinking pigment stain

I was commenting on Dave's opinion that '"fog" is a misleading term',
which implies that we pretty much _don't_ all agree on what fog is.

As my use of "global insolubilization", it means the following:

"global" because it happens through the whole gum layer. Other
applicable term would have been 'uniform' but this implies a
distribution. As Yves well observes, fog could be equated with
noise, but I don't think that at this point we know its distribution.
Probably white noise, but again, who knows. That's why I use
'global'.

"insolubilization" because what we observe is that the gum layer
is at some point more or less soluble in water. Whether
this loss of solubility is due to a crosslinking of the gum
macromolecules or if other electrochemical forces are also active is
conceptually irrelevant at this level of observation.

This is the term I prefer, but I'm not imposing it upon anyone,
so if you want to say "inadvertent (meaning non image-related)
formation of crosslinked gum" instead of "global insolubilization",
that's just fine with me. I would only object on the use of 'inadvertent'
as a synonymy for 'not image-forming'. But hey ...

Again, whether fog happens more or less frequently in actual
practice is not an impediment for having a definition for it, in my
opinion.

Tom Sobota
Madrid, Spain

At 17:43 14/12/2005, you wrote:
>I think we pretty much agree on what fog is, although I would never
>use the phrase "global insolubilization;" that seems a rather
>awkward mouthful to me. I'll continue to use the phrase I've been
>using; to me fog is the inadvertent (meaning non image-related) formation of
>crosslinked gum, and, as I said in my response to Joe's lexicon last
>week or whenever that was, in my mind it includes the dark
>reaction. I don't know about the "continuing reaction" I've never
>seen that myself.
>
> I thought Dave's point was, how often do we ever see fog in actual
> practice? I've only seen it once, when I left a coated paper
> sitting by a window and went off to get something. And I've only
> seen fog in the form of the dark reaction once, when
> I deliberately left coated paper in the dark to see if it would
> happen (it did), but I've never seen it in practice, because I
> always coat and dry one paper at a time and expose immediately.
>Katharine
>
>
>
>On Dec 14, 2005, at 7:08 AM, Christina Z. Anderson wrote:
>
>>Right on, Tom,
>>
>>fog = global insolubilization of the gum layer...
>>
>>I'll add to your list one thing they used to say but I have never found to
>>be true is they used to say certain pigments produced as they termed it
>>"spontaneous insolubilization of the gum".
>>
>>I could say that when I was doing 8 large gums at once down in South
>>Carolina where the humidity was higher, the last print to go into the water
>>would take longer development to remove nonimage "fog". Fog, up to a
>>certain point in gum practice, usually doesn't make too much difference
>>because it is removable, unlike silver gelatin.
>>
>>Does this fog, then, form an umbrella over the two terms of "dark reaction"
>>and "continuing action"? Because both result in global, non-image
>>insolubilization. In other words, back in "the day" (1800's-1900's) they
>>didn't term it fog in the first place but used these two terms to describe
>>this global insolubilization.
>>chris
>>
>>>It all depends on how you define 'fog'. To me, fog is a global
>>>hardening or insolubilization of the gum-dichromate layer which
>>>does not contribute to the formation of an image.
>>>
>>>It can be produced by any (or a sum of) several causes, among which
>>>accidental exposure to light too, of course. Others are heat, exposure
>>>to chemicals, and the simple passing of time. Surely others.
>>>
>>>The normal exposure to light of a layer of dichromated gum under
>>>a negative produces a hardening which is not physically different
>>>from a fog-producing exposure to light, but it produces an usable image
>>>since it is not global but rather differential. So we don't call it fog.
>>>
>>>This loose definition of fog could be applied to silver-gelatin emulsions
>>>too, actually.
>>>
>>>Pigment stain is different, and perhaps unique to gum, carbon and
>>>other processes using finely ground particles of pigment.
>>>
>>>But dichromate stain has a sort-of analogue in silver-gelatin emulsions
>>>when you develop with pyrogallol or pyrocatechol, for example, which
>>>also produce stain. This stain contributes to the image, however, because
>>>it is in the negative and not in the positive.
>>>
>>>If you want to see fog in gum, coat a paper and keep it in the dark for a
>>>week or two in a warm place. Then develop side by side with a
>>>just-prepared emulsion. The relative darkening of the older coat should
>>>be evident.
>>>
>>>Tom Sobota
>>>Madrid, Spain
>>>
>>>
>>>At 03:38 14/12/2005, you wrote:
>>>>I don't know all the details regarding that past discussion, but I think
>>>>"fog" is a misleading term. I consider fog to be accidental exposure,
>>>>e.g.
>>>>someone opens the back of a 35mm camera and the film gets "fogged".
>>>>Perhaps
>>>>gum paper can get fogged from ambient light levels being too high in the
>>>>darkroom, but I've never had that problem.
>>>>
>>>>Dave Rose
>>>>Powell, Wyoming
>>>>
>>>>----- Original Message -----
>>>>From: "Katharine Thayer" <kthayer@pacifier.com>
>>>>To: "alt photo" <alt-photo-process-l@sask.usask.ca>
>>>>Sent: Tuesday, December 13, 2005 12:16 PM
>>>>Subject: Rethinking pigment stain
>>>>
>>>>
>>>> > Hi gum printers,
>>>> > Because for most of my gum printing career I've printed on unsized
>>>> > paper, I developed a definition of pigment stain that I realize now
>>>> > probably applies mainly, if not exclusively, to printing on unsized
>>>> > paper. My definition required that in order for something to be called
>>>> > pigment stain, the pigment had to penetrate the paper and be indelible.
>>>> > And in my experience, when pigment stain occurred, it occurred
>>>> > immediately when the coating was applied; if the pigment was excessive
>>>> > in relation to the gum, it would stain the paper immediately on
>>>> > application.
>>>> >
>>>> > The tonal inversion thing made me rethink that idea, as I said a couple
>>>> > of days ago, and after doing some experiments with sized and unsized
>>>> > paper, I've decided I need a more inclusive definition that
>>>> > incorporates what happens on sized paper, or maybe two different terms;
>>>> > I haven't decided yet for sure.
>>>> >
>>>> > A more inclusive definition for "pigment stain" would say that pigment
>>>> > stain is whenever you get pigment in places where it shouldn't be,
>>>> > such as in unexposed areas of an image or step print. Whether or not
>>>> > that out-of-place pigment forms an indelible *stain* will be a function
>>>> > of how well the paper is sized. On sized paper, this "stain" will wipe
>>>> > off easily, whereas on unsized paper it will be indelible, but in
>>>> > either case, you've got pigment you don't want in areas that should be
>>>> > very light or paper white, hence: stain.
>>>> >
>>>> > One problem with this more inclusive definition is that it doesn't
>>>> > distinguish between stain and fog. Someone referred recently to a
>>>> > discussion from last summer where Mark showed a gum test print where
>>>> > there was color on areas where the print should have been paper white.
>>>> > I called that stain, and was told that it was fog. I conceded the
>>>> > point; when told that it could be wiped off the paper I assumed (given
>>>> > my then understanding of stain) that it couldn't possibly be stain and
>>>> > must be fog, although I didn't have a clear understanding of what could
>>>> > have caused the fog. And when that was brought up recently, I
>>>> > acknowledged I'd been wrong when I'd called it stain. But now that I
>>>> > have seen for myself that pigment stain can also be easily wiped off
>>>> > sized paper, (while still wet, of course) I'm not sure I know how to
>>>> > tell the difference between stain and fog on sized paper.
>>>> >
>>>> > They are of course different in substance, because what I would call
>>>> > "pigment stain" is just pigment, since it occurs in areas where no
>>>> > exposure, and therefore no formation of crosslinked gum, has occurred,
>>>> > whereas fog, in my opinion, would involve the formation of crosslinked
>>>> > gum.
>>>> >
>>>> > On unsized paper, excess pigment impregnates the paper as stain, and
>>>> > that's why it stays with the paper rather than dissolving away with the
>>>> > dichromate and soluble gum from unexposed areas. But on sized paper,
>>>> > even though the pigment isn't held in the paper as stain, or in
>>>> > crosslinked gum as "tone" it still remains on the paper in unexposed
>>>> > areas, as seen in the examples of "tonal inversion." This is
>>>> > interesting, but puzzling, to me. At any rate, I've satisfied myself,
>>>> > by cutting coated papers in half and exposing one side and putting the
>>>> > other side directly into water, that the "pigment stain" is the same
>>>> > on unexposed areas of exposed coatings as it is on completely unexposed
>>>> > paper, whether sized or unsized, which makes me even more confident
>>>> > that the effect has nothing to do with exposure, heat or anything else
>>>> > related to the exposure itself, but is simply pigment stain.
>>>> >
>>>> > Thoughts, anyone? I will soon be revising my page on stain, lord
>>>> > willing and the creek don't rise, to reflect the evolution of my
>>>> > thinking on this topic.
>>>> > Katharine
>>>> >
>>>> >
>>>
>>>
>>
Received on Wed Dec 14 19:04:18 2005