Re: Gum: Pigment stain and exposure

Hi Katharine, thanks for sharing experience.

My question is: have you made fresh gum / pigment mixes for each
printing or you just used a stock gum / pigment solution? If the
latter can we conclude that the pigment does something to the gum
which leads to staining?

TIA,
Loris.

----- Message from kthayer@pacifier.com ---------
     Date: Fri, 04 Aug 2006 09:31:00 -0700
     From: Katharine Thayer <kthayer@pacifier.com>
Reply-To: alt-photo-process-l@usask.ca
  Subject: Re: Gum: Pigment stain and exposure
       To: alt-photo-process-l@usask.ca

> Another thing to ponder: in my stack of oddball pieces of paper,
> there was a quarter-sheet of Arches Aquarelle that had been sized with
> acrylic medium. I had cut a piece off this paper the day before and
> printed a small tricolor on it from a file an offlist correspondent had
> sent me to try to figure out a problem he was having with his color
> balance. The tricolor printed perfectly: no stain whatever on any of
> the layers, including the middle layer which was the same mix of PR209
> I used for the test strips described below. (The file as he created it
> had a border around the image which printed paper white, so any stain
> would have been very easy to detect, and this border was pure paper
> white after the three layers). But when I cut another piece off the
> same sheet of paper and coated it with the same PR209 mix for these
> test strips, I got immediate and irrevocable stain; it was one of those
> where you know on the first brush stroke that you've got stain; the
> paper speckles immediately in a way that you can tell is going to be
> permanent.
>
> Why it would stain in one case and not in the other, when everything is
> the same: the exact same piece of paper, same pigment mix
> (well-stirred) same amount of the same dichromate, coated area about
> the same size in both cases, same amount of brushing-smoothing, same
> light, same environmental conditions, and the exposures for the print
> were within the range of exposures for the test strips. But if the
> very same things can yield such different results for the same person,
> it should hardly be surprising that different things yield wildly
> different results, or that different people using the same things often
> get different results. Just another reminder that one test does not a
> finding make...
> kt
>
>
> On Aug 3, 2006, at 1:47 PM, Katharine Thayer wrote:
>
>> Okay, here's something to wake y'all up, since people are getting
>> restless about getting no mail from the list:
>>
>> I've been printing PR 209 (quinacridone red) at four exposures,
>> from underexposed to overexposed, on samples of all different kinds
>> of paper. (I've got a little stack of paper odds and ends that
>> I'm trying to use up). My goal was to try to see if it's true, as
>> is often alleged here, that stain is related inversely to
>> exposure, in other words that underexposed gum is more likely to
>> stain than gum that has received more exposure. I figured if it
>> were true, this effect would have to show up if I did a bunch of
>> test strips at different exposures. After a couple of days of
>> this, I have about 20 sheets of paper with four test strips on
>> each, exposed at 1, 2, 3 and 4 minutes. Some of the papers are
>> stained, some aren't. But in every case where there is stain, the
>> stain is even across all exposures; there isn't more stain where
>> it's less exposed (nor is there more stain where it's more
>> exposed). The stain is simply constant across the entire coated
>> area on the paper, which tends to support what I've said before,
>> that stain is independent of exposure. All of these papers were
>> developed for 1.5- 2.5 hours, since they were developed for the
>> most-exposed strip, which was well over-exposed. The variation
>> in the time required to develop the 4-minute exposure reflects the
>> difference in speed between the different papers. Mark, I think,
>> was asking a while ago if there are processes other than platinum
>> in which, everything else held constant, different papers print
>> with different speeds. I answered "Yes, gum." This experiment
>> shows the truth of that assertion. I wish I could scan these for
>> you, but my scanner is still in the shop.
>>
>>
>> A result worth noting: A piece of Lana that had been sized with
>> glutaraldehyde stained an overall soft pink, while glyoxal-sized
>> paper stained not a whit, nor have I ever had glyoxal give pigment
>> stain. I'm not drawing any particular conclusion from this ; it's
>> just more data for the collective database.
>>
>>
>> Katharine
Received on 08/04/06-11:43:57 AM Z