[Alt-photo] Re: Brushing gelatin on paper

[Ryuji Suzuki]

Regarding the yellowing of the gelatin, I recall some people reported the
same issue before. Those people used formaldehyde or glyoxal as their hardener.
These agents were typically used in rather strong concentrations (as they are
somewhat ineffective hardeners) and excess agents can get oxidized to yellow
the paper. When I used to do these things, I used glutaraldehyde (easiest to
buy, fast reaction), bisepoxides (slow reaction but no volatile fume coming out)
or s-triazine hardeners (fast reaction, not volatile but nasty chemical to handle).
These can be used in much smaller quantities to effectively harden gelatin and
I didn't have yellowing problem. If interested, I encourage you to dig up the
archive.

Also, I found foam brush to be a rather poor tool for coating, as it can nap
the surface of the paper. I found a very good tool made for interior wall paints
and also posted a report to this list, probably 5 to 10 years ago.

--
Ryuji Suzuki
"Don't play what's there, play what's not there." (Miles Davis)




Luciano Teghillo wrote:
> Hi All,
>
> I have been looming in the back an enjoyed the wealth of information all of
> you share. Of course I have not shared nothing because...well, I am just
> getting my feet (actually my paper) wet, as you will see.
>
> I have a question on brushing gelatin on paper. I have prepared the usual
> mix of 30% gelatin and kept it at about 45-50 C and brushed it with a foam
> brush on the print side of my Fabriano Rosaspina paper.
> I brushed on two coats, after letting the first one dry for a day. This
> morning I was getting ready to harden the paper in formalin but I had the
> bad idea of comparing my sheets of paper with a couple of scraps of papers I
> have from two previous workshops.
>
> The papers I was using as a comparison where noticeably more yellow (both
> Fabriano Artistico, Traditional White) when looked on a light table, so my
> doubt is that my paper did not receive enough gelatin. Of course I cannot be
> sure because the samples I used for comparison have been tray sized and not
> brush sized. Also, for least one, the gelatin used is similar to Knox
> (Paneangeli for the Italians), while I used Photographers' Formulary Hard
> Gelatin (250 Bloom).
>
> Also when I compare my sized paper against a sheet of the same unsized
> paper, I cannot see any discernable difference, even under an 8x loupe.
>
> When brushing I load the foam brush, and move horizontally, vertically and
> diagonally with speed (not quite the same as when you coat with pigment, but
> almost), and make sure the brushing is uniform by looking at the surface
> from an angle.
>
> Maybe I brush to fast and "pull" the gelatin too much that it does not get
> into the paper?
>
> Since I have already wasted and entire set of Fabriano Artistico that I
> presume I sized incorrectly, I want to make sure this time I do it
> correctly.
>
> Maybe is something totally unrelated to sizing. Maybe I should harden the
> gelatin before making a comparison.
>
> I  tried to scan the paper samples (mine and those used as a comparison)
> it's useless. You can only see the paper ridges and valleys, but nothing
> else.
>
> I have posted however two images on a previous test I did. The only thing
> different between the two tests is the paper. Everything else is the same,
> done on the same day, developed for the same time, etc.
>
> - http://www.lucianoteghillo.com/images/test01.jpg - This paper was sized by
> someone else.
> - http://www.lucianoteghillo.com/images/test02.jpg - This is the paper I
> sized on a previous batch.
>
> Feeling frustrated....
>
> Thanks for any help,
> Luciano
>
>
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