U of S | Mailing List Archive | alt-photo-process-l | Re: brush vs tray size for gum

Re: brush vs tray size for gum


About the humidity:

I live in a very humid climate and have no problems printing gum in high humidity, but a few weeks ago I found that when the humidity plunged to an almost unheard of 17%, exposing even at 3X my normal exposure time wasn't nearly enough exposure; the gum just ran off the paper in development. According to a graph I found in some information from a printing industry group, that much of a drop in humidity should necessitate 8x the exposure to harden dichromated gum arabic to the same degree. But before I tried increasing the exposure by that much, the wind changed and the humidity went back to 93%, and suddenly everything went back to normal.

So my first thought was that your development was slow and difficult because with the high humidity, you were using exposure times that were too long for the conditions, and consequently overexposed the gum.

But this explanation stops making sense (there's those pesky data, interfering with perfectly good theories again) when it comes to your observation that unsized paper printed fine and developed well in a reasonable time.

But your observation that with the unsized paper the development time is closer to the normal development, implying that it's still greater than normal, indicates to me even with the unsized paper you're getting some effect of the humidity on speed of the gum, so I think that may still be probably somewhat of a factor.

But I also wonder whether due to the increased humidity, the sizing might not have been completely dry before printing; obviously if unsized paper works better than sized paper, there's probably something about the sizing that's contributing to the problem, as you surmise.

About whether sizing needs to be "aged" before printing:

I've never found this to be true, as I'm always sizing paper on the fly and printing as soon as the sizing is dry, and I keep wondering if it's just another one of those myths that keep popping up or if there's something to it. But one thing I have seen, is that if the sizing isn't completely dry when printed (and in my humid climate even brush-sized paper does have to be dried for several hours, if not overnight) then I've sometimes seen bright yellow dichromate stains in the paper, and also pigment staining. So while my own experience doesn't support the idea that sizing has to be aged per se, it does suggest that it's important to be sure that the sizing is dry before printing.

As to brush vs tub, I think it's probably a matter of personal preference. I prefer brush-sizing because there's less glyoxal-laced gelatin to dispose of afterward, and I find that as long as I keep the paper warm and the gelatin warm, it brushes out easily enough to get a good even coat.

On Sep 26, 2006, at 8:49 AM, kerik@kerik.com wrote:


I agree that tray sizing is a lot of mess and hassle for no substantial
benefit. Plus, why do the sizing in 2 steps when it can be done in one? I
use either a glass rod (puddle pusher) and/or a brush. I add the hardener
(formaldehyde in my case) to the sizing just before sizing each print.
Three drops of formaldehyde and 5 ml of 3% sizing easily does an 8x10 to
11x14 print. In these tiny amounts, exposure to formaldehyde (or whatever
hardener one uses) is minimal. I get very even sizing this way. A little
bit of curl to the paper, but nothing that causes any problems.

I tried B.M. glut and did not like the results. It resulted in slower
development and considerably more staining than with formaldehyde.

As for sizing with unhardened gelatin, that sounds like another in a long
line of T King's erroneous hyperboles.

Speaking of gum, I taught a gumover workshop in Philladelphia this past
weekend for www.projectbasho.org. On sunday it was 80 degrees F and 82%
humidity in the darkroom. That's the first time I've printed gum in
sauna-like conditions and it created some hassles with very slow
development and the need to intervene with some brute force measures
(brushes, fingernails, sandpaper). Anybody have similar problems printing
gum in high humidity? The conditions seemed to cause problems with the
sizing in particular because development was much closer to normal when I
did a single coat of gum on unsized paper right out of the plastic bag. I'm
speculating that the humidity either prevented the gelatin from hardening
completely or it allowed the gum solution to soak into the sizing a bit
rather than sitting on top. Despite the problems, I believe a good time was
had by all. Although I always want things to go smoothly during the
workshops, it's good for the students to learn how to deal with problems
when they come up.


Original Message:
From: Christina Z. Anderson zphoto@montana.net
Date: Tue, 26 Sep 2006 08:08:22 -0600
To: alt-photo-process-L@usask.ca
Subject: brush vs tray size for gum

Hi All,
This weekend was time for sizing paper, and since I was doing small sizes
(11x14's) I decided to tray size instead of brush size to see if it had any
added benefits to brush sizing.

I was sizing with gelatin glutaraldehyde as usual. I did use a piece of it
right away, same day, and had no problem with the sizing not being hardened
and producing "magenta squares" as did Carmen. However, I was using glut
that I bought from a medical supply house (now available at the
Photographer's Formulary) and not Black Magic. The gelatin on my paper was
not slimy in any way so I know it was hardened. I am still not sure why
Carmen got that problem, and am wondering about the suitability of Black
Magic, therefore, with its added sulfite. It sounds like the same result I
had when I tried Terry King's advice to use unhardened gelatin and got

With tray sizing and cautions with glut, I gelatin sized the paper first,
and then the next day I soaked the sized paper OUTSIDE in a tray of 50ml
glut to a gallon of water. That worked well, but I would only tray size if
the hardening part could be done outside to minimize fumes produced by the
surface area of a whole tray of hardener, whatever type--glut, gly,
formaldehyde. (When I brush size I keep the solution capped inside a
and pour out a cup at once.) The gelatin paper went in "slimy" feeling, and
went out unslimy.

The paper works fine but I learned a couple things: paper tray sized with
gelatin will sink to the bottom, not float as does brush sized paper
Arches) so if I am going to leave the paper soaking for a while it needs to
be face up. I learned that the hard way. Back to floaters and sinkers, Mark.

The paper does curl less than brush sized, but it doesn't seem worth the
added trouble of trays. This is the only benefit I can see. Oh, maybe more
evenness of sizing? I don't know this one yet...will have to print all

My husband set up an ingenious "clothesline" for me--a rung ladder on its
side has plenty of hanger-ready rungs.

I learned another thing the hard way: I printed 4 prints on the unsized
shrunk paper with a cyanotype layer, put the paper through the hot gelatin
sizing process and didn't THINK that the 140-whatever degree gelatin would
shrink the paper even more and make registration a B---H but you bet it
did--warped and shrunk. Luckily only 4 prints ruined. DUH. Or, as Clay

The bottom line is that brush sizing is sooo much easier and works well and
uses way less gelatin--I sized 24 11x14s with a a liter of 3%, and normally
I can do that many 16x20s with the same. I don't think even with small
I would tray size...

That's all my truly exciting weekend experience!


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