From: Jeffrey D. Mathias (jeffrey.d.mathias@worldnet.att.net)
Date: 02/06/01-09:56:01 AM Z
Peter Fredrik wrote:
> Yes I did only evaluate in one direction but this did not seem to make any
> difference to the final results I got from the tests on paper from
> differing sources, as I had no way of knowing which way the grain was
> running, ...
One way to check the direction of grain is to humidify the paper on one
side and observe the curl. The paper should curl so that the trough of
the curl is parallel to the grain. The paper is usually packaged with
the same orientation.
> ... I think we can discount these small changes a
> greater problem lies with relative humidity which it seems expands and
> contracts to a greater extent....
I agree humidity changes can make registration challenging.
I have also noticed size differences between the directions up to 1/8 of
an inch over an 8 inch size of papers I typically have used for Pt/Pd
printing. I would consider this significant enough to check both
directions for any paper used and requiring registration. Also the
final dried size may differ from the working size (after coating,
especially with humidity), and the pre coat size.
I find that if the paper is preprocessed (no coating, water bathes for
typical times and dried, subsequent shrinking can be made minimal, but
may still occur for some papers. (Example: Biefang 360 seems to shrink
twice, and the first time shrinks noticeably different between the
directions.) However the sizing of the papers may be affected so that
subsequent coating soaks in and through too much. And, humidity
differences can still make a change.
It is probably a good idea to check each new batch of a paper for any
parameters that may influence results. For example: print quality for
particular process, strength to survive processing, which side works
best, and dimensionally stability if registration will be used. Within
a batch of paper, one may wish to candle for interior defects or inspect
the surface for scratches. Part of the paper selection (and compromise)
may be one that is more dimensionally stable to help with registration.
Checking each new batch is good because even if a manufacturer has
reliable consistency, they may "improve" a paper without (or with)
notice that may completly alter its use with an alternative photo
process.
Has anyone tried laminating the paper negative so as to render it
impervious to moisture. Some of the laminating films are very thin.
But perhaps better, select a paper to print on that has the same
expansion characteristics as the paper negative.
-- Jeffrey D. Mathias http://home.att.net/~jeffrey.d.mathias/
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