RE: Gum image has reversed

Yes, a nice example of very extended tonal inversion. Don't throw it away :-)

But the cause is not necessarily different, IMO. Your colorized negative is
probably less transparent to UV wavelengths and as a result you have an
underexposed copy.

'Colorizing' inkjet negatives is a recognized way to add UV density, so it
makes sense that your negative is much denser even if you don't perceive
this visually. It all depends on the inkset you use, actually. And hence the
probable subexposition.

I would be interested in seeing what happens if you expose this same
negative for more (even _much_ more) time.

Tom Sobota
Madrid, Spain

At 20:53 09/01/2006, you wrote:
>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 15:43:44 2006