[pure-silver] Re: curled fiber edges
- From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
- To: <pure-silver@xxxxxxxxxxxxx>
- Date: Wed, 23 Apr 2008 11:16:36 -0700
----- Original Message -----
From: "Bogdan Karasek" <bkarasek@xxxxxxxxxxxx>
To: <pure-silver@xxxxxxxxxxxxx>
Sent: Wednesday, April 23, 2008 7:05 AM
Subject: [pure-silver] Re: curled fiber edges
Hi Nicolas,
Pakasol? More details on this; looks interesting;
solution to a persistent problem?
Cheers,
Bogdan
Pakosol is a print flattening solution. Most of these
are solutions of glycerin with perhaps other substances.
They are humectants intended to keep the moisture content of
the emulsion high. There have been questions about the
effects on the longevity of images when such flatteners are
used. I don't know if Pakosol is still made. Pa-Ko made
processing equipment for photofinishers including large drum
dryers. A treatment like Pakosol is used with heated dryers
to avoid over drying and consequent brittleness of the
emulsion and substrate.
Any flattening process is ultimately aimed at balancing
the moisture content of the emulsion versus the support.
Curling of paper (or film) is due to the different rate of
shrinkage of the emulsion and support at various amounts of
moisture content. The emulsion side tends to shrink more
than the paper so the usual curl is toward the emulsion
side.
Cockling or rippling near the edges is related to curl
but is due to some non-uniformity in the coating. I used to
have this problem especially with older Agfa papers. If its
not too severe the dry mount press flattening process will
cure it but, if severe, there may be damage at the edges of
the print requiring trimming. I used the word frilling in my
post because I couldn't think of "cockling", frilling is
really something else but is similar to a very fine cockling
at the edges but usually with loosening of the emulsion.
This must be trimmed off.
What has been missed in most of the posts is that the
paper backing must be dried more than the emulsion in order
to equalize the shrinkage. When using heat and mild
pressure, as in a dry mount press or hand iron, the emulsion
side must be protected by a moisture impermiable covering
such as dry mounting releas tissue. Otherwise it will be
dried out and the print will probably curl again. Also,
because there is to some extent a sort of molding of the
emulsion, its important to cool the ironed or pressed print
under a flat weight leaving the release tissue in content
with the emulsion to keep moisture from being lost.
Drying on screens is one way to reduce the difference in
shrinkage because, when the emulsion is in contact with the
screen it can not dry out as fast as the paper support,
which is in direct contact with the air. Old style screens,
made of cheesecloth, are probably better than modern ones
made of plastic screening, because they tend to absorb
moisture from the print and hold it in the emulsion.
Old time photofinishers used to treat prints in a
mechanical straightener. These ran the paper across a
knife-edge with the support against the knife edge to
stretch the emulsion and substrate. I don't recommend these
although they work. One can achieve the same thing by
running a print across a sharp table edge. If the substrate
is too dry it will crack and flake off. That used to happen
with drum dryers when the heat was turned way up to shorten
drying time.
Again, I've posted a complete dry mouting procedure to
this list and to a couple of usenet groups in the past, the
correct flattening procedure is part of this. Its easy to do
on a press and will work with a hand iron. I will repeat the
thing here if requested.
---
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx
=============================================================================================================
To unsubscribe from this list, go to www.freelists.org and logon to your
account (the same e-mail address and password you set-up when you subscribed,)
and unsubscribe from there.
Other related posts:
