RE: Gum image has reversed

Recently I have come across a different cause for the tonal inversion than
those discussed in this thread so far. I experimented with colorizing a
digital negative with an orange-ish layer and the resulting image turned out
to be reversed.

I've just uploaded it to
http://katemocak.slide.com/c/Gum+bichromates/5012705. It is not yet
finished, I still plan to add more layers, but the reversal is already visible.

I am convinced that the effect has something to do with the colour of the
negative, though I'm not quite sure how to explain it.

Kate

----- Original Message -----
From: "Katharine Thayer" <kthayer@pacifier.com>
To: alt-photo-process-l@sask.usask.ca
Sent: Mon, 09 Jan 2006 10:14:24 -0800
Subject: Re: Gum image has reversed

> A couple more comments about "tonal inversion":
>
> To say it's somehow related to exposure is to say the obvious, as the
> whole inversion thing requires different levels of exosure to be
> present. With no exposure, the entire paper would be stained, rather
> than there being a reverse image, which sort of goes without saying.
> But it also doesn't make sense to say that it's caused by
> underexposure, because underexposure can't cause a reversal image
> unless the gum is overloaded with pigment to start with. And if there
> is excess pigment present, exposing more won't make the problem go
> away, as is shown by the partial inversion on the "for fun" page I
> showed the other day:
>
> http://www.pacifier.com/~kthayer/html/tricolorfun.html
>
>
> where the image is correctly exposed, but is still partially
> reversed as the result of overpigmentation.
>
> For a complete reversal of tones, where what should be the darkest
> tones are the lightest, the bulk of the emulsion has to have left
> from the areas of greatest exposure, one way or another. This
> leaving of the emulsion can happen as a result of underexposure, but
> it can also happen as a result of flaking off of the pigment, as a
> result of severe overpigmentation resulting in a too thick layer, or
> from printing on a hard surface resulting in the floating away of the
> hardened gum, as in the experiments on glass some of us were doing a
> couple of weeks ago.
>
> Tonal inversion will occur on well-sized papers; it isn't a question
> of sizing or not sizing. It's all about pigmentation, how much
> pigment a particular gum can hold in suspension. If you're not
> getting staining or inversions, your pigment loads are no doubt well
> within the capacity of the gum. I don't think it's useful to make
> characterizations about the amount of pigment we use in ordinal
> terms, because we all mean different things by those terms. For
> example, some time back, Chris said she uses a huge amount of
> pigment, and gave the amount of pthalo she uses as an example.
> Curious, I figured out how much pthalo I use, and found that we used
> the same amount of pthalo paint as a percentage of total emulsion,
> although when I talk about how much pthalo paint I use, I say I use
> a very small amount, since it's so much less than I use of many other
> pigments. My point is that it wouldn't be very useful to assume
> that because Chris says she uses a lot of pigment and I say I don't
> use very much pigment, that means Chris uses more pigment than I do.
> My feeling about this whole pigment concentration issue is that gum
> knows how much pigment it can hold, and will let you know if you've
> given it more than it can carry, and that all of us who successfully
> print gum are probably using about the same amount of a given
> pigment, regardless of the label we give to that amount.
> Katharine
>
>
>
> On Jan 8, 2006, at 8:56 PM, Katharine Thayer wrote:
>
> > Hi Bruce,
> > 1. The negative image, in my opinion, is the result of too much
> > pigment. There's been some discussion of this fairly recently (in
> > the last two months) on this list. Not everyone agrees with me
> > about this, but I'll bet if you'll cut back on your pigment, you'll
> > get a positive image. The reason it's black where there should be
> > white, or light tones, is pigment stain, and the reason it's white
> > where it should be black is that the emulsion was so thick (pigment-
> > laden) that it flaked off.
> >
> > 2. I don't know what to say about your gum. I don't know the
> > current Photographer's Formulary gum, although I loved an earlier
> > version. I think the two problems are related to pigment
> > concentration; with a heavy (but not overly pigmented) pigment
> > load, you will get a high contrast image. It looks like with one
> > gum (the prepared gum) you're just under the limit for the amount
> > of pigment that the gum will hold in suspension, and with the other
> > one, you're just over the limit and that's why you got the inverted
> > image.
> > Katharine Thayer
> >
> >
> > On Jan 8, 2006, at 8:40 PM, Bruce Pollock wrote:
> >
> >
> >> I'm new to the list and will apologize in advance for the barrage
> >> of questions which I'm going to unleash over the next little
> >> while. My frustration level is running quite high. However, for
> >> the moment, I will try to limit myself to two main problems.
> >>
> >> First, a little background. I dabbled in gum dichromate about 25+
> >> years ago and had some satisfactory results, but never really
> >> stayed with it. I always wanted to get back into it and so, here
> >> I am. I still have the 1 lb. jar of Potassium Dichromate I bought
> >> back then and still have some Gum powder as well. Whether the age
> >> of my chemistry has any bearing on the results I've experienced,
> >> I'm not sure. I really can't see how Pot Dichr can "go bad" but,
> >> you never know.
> >>
> >> My first question relates to the first usable print I've obtained
> >> after many, many failures. I finally have something that suggests
> >> I have a chance of success, but the print has reversed to
> >> negative. Can anyone explain this? The detail is quite good, but
> >> I have a negative, not a positive. Here are some details about my
> >> method:
> >>
> >>
> >>
> >>> Lanaquarelle Medium Watercolour 140 lb. Paper, *not* sized
> >>> Analogue 4x5 negative made in-camera on Tri-X film
> >>> #2 blue photoflood light source about 25 inches from neg
> >>> 20 minute exposure
> >>> Emulsion made from 2.5 ml gum, 2.5 ml potassium dichromate
> >>> solution and about 0.5 gm Daniel Smith Lamp Black pigment
> >>> Still development for about 10 minutes brought up reasonable
> >>> density -- my fear in letting in go on much longer was that I'd
> >>> loose the entire image (just like the first dozen or so failures).
> >>>
> >>>
> >>
> >> I realize that I should probably size the paper and that Lamp
> >> Black is not the best starting pigment, but I was just trying to
> >> get myself into the ball park on emulsion and exposure times.
> >> However, I'm stumped by the negative product.
> >>
> >> My second question relates to the type of gum arabic I should be
> >> using. This success (if you can call a negative print a success)
> >> came after I switched back to my old gum arabic powder (25+ years
> >> old). The gum was a fine, white powder which I put into solution
> >> using the formula in "The Keepers of Light" by William Crawford.
> >> My earlier failures had been done using some Gum Arabic pre-mixed
> >> solution recently purchased from Photographers Formulary. Using
> >> the pre-mix I got virtually no results -- anything I got was
> >> basically a "soot and chalk" type print where the shadows went
> >> black and the highlights blew out. Nothing in between. No detail
> >> at all.
> >>
> >> Can anyone explain the lack of results with the pre-mix Gum
> >> Arabic? Should I stick with the powdered form and mix it myself?
> >> The fact that I got *some* results from the powder suggests to me
> >> that the pre-mix is somehow at the root of my earlier problems
> >> where I got soot and chalk.
> >>
> >> Many thanks in advance -- all advice gratefully received.
> >>
> >> Bruce Pollock
> >>
> >>
> >>
> >>
> >
> >

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Received on Mon Jan 9 14:01:37 2006