Re: GUM PRINTING QUESTION

From: Katharine Thayer ^lt;kthayer@pacifier.com>
Date: 08/11/05-04:53:10 AM Z
Message-id: <42FB2E0A.5461@pacifier.com>

Christina Z. Anderson wrote:
>
> Katharine,
> As I can always predict, there is nothing I ever post that you
> have found to corroborate in your gum practice, except for one thing that we
> agree on--that using too hot water for a preshrink soak may interfere with
> the sizing in a paper. I suspect I have misquoted that, too, but you'll
> correct it I'm sure.

No, I believe that's right.

But I think you've completely missed my point here.

There is a type of dichromate stain that is yellow, that as I've just
demonstrated contains active hexavalent chromium, but that is very much
a *stain,* meaning that it doesn't come out in water development. In
this kind of stain, dichromate gets trapped into the sizing somehow,
and no amount of soaking will get it out; it has to be removed with a
clearing bath. As I said, I've only seen this two or three times, I
think it occurs with certain paper/sizing combinations, and perhaps in
association with humid conditions. As I said, I was only able to
reproduce a soft yellow stain yesterday by attempting to reproduce these
conditions-- when I saw it occur spontaneously before, it was a brighter
yellow. But this yellow stain is the stain I am talking about when I
speak of a yellow (unreduced) dichromate stain, when I said that a
yellow stain, like the one Judy reported, would probably continue to
turn brown with exposure to UV. You responded

> I did this last summer and we had a discussion on this then; yes, the sun,
> in fact, does bleach the yellow dichromate out of the print

 I said that was confusing to me, since I'd been under the impression
that you meant the brown dichromate stain when you said that dichromate
stain will bleach in the sun. While you didn't respond to that implied
question, your account below seems to suggest, since it no longer
includes the word "yellow" that what you really mean is the usual brown
dichromate stain, not the yellow dichromate stain that I'm referring to.
It seems to me that the answer is fairly clear: a tan or brown
dichromate stain, being already reduced, will bleach when exposed to
sun; a yellow dichromate stain, containing unreduced chromium, will
darken and turn brown when exposed to sun, and it would be misleading to
suggest that a yellow dichromate stain could be left alone and expected
to remain stable. This is what I said, if I remember correctly, in the
first place.
Katharine

>
> Let's go back to my story, and I am sticking with it:
>
> 1. A person asked if clearing was necessary.
>
> 2. A person also asked if colors faded with UV exposure once a gum print
> was done.
>
> 3. I reported that in old literature, clearing was always optional. Sil
> Horowitz concurs. I trust the old literature on quite a few things--not
> all-- because at that time there were many gum practitioners, and therefore
> a much larger body of experience to draw from than we have today.
>
> I also reported that in old literature if a clear were felt to be necessary,
> it was sometimes recommended to place the gum print out in the sun and it
> would "clear" with sunlight. I couldn't believe this would be the case. I
> tried it. It worked. I then tried it with both gum and albumen. I tried it
> with no pigment. It worked the same every time.
>
> This "clear" method was in a number of the old books. It wouldn't be a
> recommended clear method because who wants to put prints in the sun anyway?
> Still, it intrigued me.
>
> I no longer clear anyway, and I no longer worry about NOT clearing, and I
> don't worry about UV exposure on pigments once a gum print is done, within
> reason (as long as I am using lightfast pigments, of course).
>
> The fact that you got brown leads me to believe that you had remaining
> unexposed and active dichromate in your paper. Maybe you didn't develop
> long enough, who knows what could be your case. Whatever, this is not the
> same situation I am talking about, nor does it relate, in my opinion, to the
> original poster's question--does one need to clear? I assume the original
> poster had developed his print long enough to remove any remaining active
> dichromate from the paper.
>
> I also know that the difficulty Mungo Ponton had with his dichromate only
> exposed paper in 1839 is that the image faded to a pale green. It was not
> permanent. From this ensued a number of methods in the early years of
> dichromate printing to make this fading image remain, by adding different
> chemicals or baths.
>
> It stands to reason that active dichromate will brown to a considerable dark
> brown in the sun. I did that, too, last summer, with dichromated gum left
> in cups, both exposed and unexposed, both painted on paper and not painted
> on paper, and with dark reaction and continuing action both, over a period
> of a week, I observed a nice molasses brown occur.
> Regards,
> Chris
>
> >> Katharine Thayer wrote:
> >> >
> >> > Chris,
> >> > Well, I guess I'm confused, because I thought that in the issue of sun
> >> > bleaching dichromate stain, you were talking about a brown (reduced)
> >> > dichromate stain, not a yellow (unreduced) dichromate stain.
> >>
> >> Because if whatever it is that causes that rare bright yellow stain
> >> (I've only seen it once or twice, when I was testing a lot of different
> >> paper-sizing combinations) somehow arrests hexavalent chromium in the
> >> hexavalent state and renders it stable (or at least unreducable) in that
> >> state, that would be a rather remarkable finding.
> >
> >
> > Curious, I tried to create a bright yellow dichromate stain (I've had an
> > idea about what might cause this) but was able to create only a soft
> > butter-yellow stain, not the bright yellow characteristic of hexavalent
> > chromium (but still definitely yellow, not the tan or brown stain that
> > is usually seen in gum practice). This yellow stain, after being
> > developed half an hour and dried, did turn brown when placed outdoors
> > half covered; the yellow was completely replaced with tan/brown in less
> > than an hour. While there was no direct sun, there was enough UV to
> > create a brown dichromate stain within two minutes on a (separate) sheet
> > of paper coated with dichromated gum, that I placed beside the other one
> > for a rough test of the available UV.
> >
> > The brown stain that resulted from the yellow stain being placed outside
> > on a cloudy day didn't bleach within the four hours of remaining
> > daylight.
> >
> > One test never proves anything, of course, but on the basis of this
> > observation I wouldn't recommend that people assume that a yellow
> > dichromate stain will stay yellow, or will lighten, when exposed to UV
> > over time. My observation would suggest that yellow chromium can still
> > be reduced to another form in the presence of UV, even when it is
> > trapped within the sizing/paper as a stain, and even if the UV isn't in
> > the form of direct sun.
> >
> >
> > Katharine
> >
Received on Thu Aug 11 11:49:50 2005

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