Re: Gum: Pigment stain and exposure

On Aug 4, 2006, at 10:44 AM, Loris Medici wrote:

> 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?

The gum/pigment mix was the same stock mix in both cases; that's why
I specified that it was the same mix. I didn't mean it was mixed
from the same formula, I meant it was poured from the same stock mix,
well-stirred before each draw. All the test strips from the same
day as the anomalous stained test print on acrylic medium were
printed from the exact same emulsion. I printed some ten sets of
test strips that day and it was only two or three that stained, and
not the last ones. And I printed another ten the next day, from the
same stock mix, with similar results; a few stained, but most
didn't, and the ones that stained were randomly distributed
throughout the day's printing.

> If the latter can we conclude that the pigment does something to
> the gum which leads to staining?

No, as I said above, there's nothing in the data that would lead one
to that conclusion. But maybe you've missed my point, which was that
concluding anything from one test print is not a good idea. The
reason I brought up this contradictory result was to show how
misleading it can be to draw conclusions from one observation; you
need a generous sampling of observations from the distribution of
possible results before you start drawing conclusions.

But to answer your question about whether stock pigment/gum mixes
that sit for a long time CAN change in such a way that leads to
staining: it depends on the gum. I've found that Daniel Smith
premium gum doesn't sit well; it tends to dry out over time; as a
result the ratio of pigment to gum does go up and staining can
occur. But this is something that happens over months, not
overnight. But pigment/gum mixes of seldom-used colors that were
mixed ten years ago with the old Photographers' Formulary gum are
still as fresh and liquid and print as stainfree as the day they were
mixed.

Katharine

>
> 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 08/04/06-02:39:03 PM Z