Re: Rethinking pigment stain

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 10:44:51 2005