Re: Rethinking pigment stain

Katharine,

all I said on this study was based on my misinterpretation of what you said
about it, (Mille excuses) 1000 excuses. I also said at the end on this
dichro stain comment that it wasn't resolved or still part of the unexplored
territories.

Yves

----- Original Message -----
From: "Katharine Thayer" <kthayer@pacifier.com>
To: <alt-photo-process-l@sask.usask.ca>
Sent: Wednesday, December 14, 2005 12:47 PM
Subject: Re: Rethinking pigment stain

>
> On Dec 14, 2005, at 7:58 AM, Yves Gauvreau wrote:
> >
> > I know this doesn't give a satisfactory explanation as to what causes
> > dichromate stains. Katherine as refered us to a PVA dichromate study
> > from
> > which she seems to infer that overexposure is the cause of these stain
> > because an excessive amount of activated dichromate molecules is not
> > bounded
> > to colloid molecules (in this study all colloids where made insoluble
> > thus
> > where bounded with dichro).
>
> Yves, maybe you didn't get the message where I clarified that in the
> particular case of the dichromate stain that I showed you, I
> deliberately caused the dichromate stain by overexposure in the sun,
> because I know from practical experience that gross overexposure is the
> best way I know to reliably create dichromate stain. But I certainly
> wasn't suggesting that overexposure is the only way to create
> dichromate stain, and in fact there have been many lively discussions
> here with many people reporting their own observations about dichromate
> stain and many theories advanced. As far as I'm concerned, there may be
> many possible different causes for many different cases of dichromate
> stain.
>
> I wouldn't quite agree with your characterisation of Duncalf & Dunn,
> but that's irrelevant to this discussion). What happens to the excess
> reduced chromium is a question both beyond the scope of Duncalf &
> Dunn's research and the state of current knowledge about the process,
> as far as I know, so I wouldn't want to be misinterpreted as having an
> opinion about that finer theoretical point one way or the other; all
> I'm saying is that in my practical experience, for whatever reason,
> excess exposure simply produces dichromate stain and then more
> dichromate stain, without adding any particular benefit, and Duncalf &
> Dunn's observation that dichromate continues to be reduced after the
> colloid has become insoluble seems to be in concert with my personal
> observation. But I wouldn't make any more of it than that, because I
> don't think we know enough about it to make any more of it than that.
> Katharine
>
>
> > I suppose one could say just increase the number
> > of available colloid molecules such that you don't have a surplus of
> > dichromate. I'd be curious to here ear from those who suggest to use a
> > 2:1
> > gum / dichro ratio, about their dichromate stain??? Assuming this
> > simple
> > adjustment could resolve the dichromate stain problem, then the
> > exposure
> > scale could be largely extented without causing those infamous stains
> > and
> > leave us with just beautiful clear gum and some pigment of course but I
> > don't know if this is true so lets forget about it here.
> >
> >
> >
> > ----- Original Message -----
> > From: "Tom Sobota" <tsobota@teleline.es>
> > To: <alt-photo-process-l@sask.usask.ca>
> > Sent: Wednesday, December 14, 2005 5:55 AM
> > Subject: Re: Rethinking pigment stain
> >
> >
> >> 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 12:26:58 2005