Re: Coating prints with polyurethane wood finish

What do you mean by "Dmax increased by 1 stop" in the ziatype test
print? Did you mean that 1 stop less exposure to reach Dmax, or you
found 0.3 unit higher Dmax?

Anyway, I see two potential problems in using polyurethane. One is the
durability of polyurethane itself. Another is how effective it is in
providing a barrier against gaseous oxidizing agents.

I am no expert in this area but I think only some water based
polyurethane is recommended for archival artwork on paper.

The second issue can be tested by peroxide fuming test. I don't
really see a better way to test for this. I've been using this to test
efficacy of my toning solutions for silver gelatin prints.

Regarding pollutants coming from the back of the paper, I bet some
papers are better than others. I'd expect paper with generous amount
of hydrophobic internal sizing material would provide better barrier.

Ryuji

From: Loris Medici <mail@loris.medici.name>
Subject: Coating prints with polyurethane wood finish
Date: Tue, 31 Jan 2006 20:13:37 +0200

> http://duke.usask.ca/~holtsg/photo/current/0273.htm
>
> One more thought
> Coating the the front of a colloidal silver image (Kallitype, Vandyke,
> Argyrotype) with polyurethane may protect it from pollutants also -
> since it seals the front of the paper. So maybe one would not need to
> tone (therefore alter the image color) the print in order to increase
> its permanence(?). What do you think?
>
> TIA,
> Loris.
>
> P.S. I know the pollutants may attack from the back of the paper, but I
> think the effect may not be as strong(?).
>
Received on Thu Feb 2 00:04:28 2006