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Subject: Glassine for storage of negatives

Glassine for storage of negatives

From: Ellen McCrady <abbeypub>
Date: Wednesday, April 8, 1998
I agree with the main point that Jonathan Farley makes in his March
26 message, where he says that glassine should not be used for
storage of negatives.  However, I think he would have done well to
omit his description of various aspects of paper manufacture and
deterioration, because it is not necessary to do this in the first
place, and because most of his descriptions are inaccurate in the
second place.

If one wants to convince people not to use glassine for storing
negatives, all one has to say is that glassine is advised against by
the ANSI standard IT9.2-1991, and that Henry Wilhelm, in his book,
"The Permanence and Care of Color Photographs," advises against it
on p. 467.  Neither the standard nor Wilhelm's book mention the
supposed procedures and decay processes Mr. Farley describes; they
just say that under damp conditions, the glassine (which is
hygroscopic, and smooth like the surface of an emulsion) will stick
to the soft emulsion of the photograph and often imbed itself in it,
so that neither physical nor chemical methods can remove it.  This
effect is especially pronounced when the negatives or photographs
are stored under a weight, or in a tightly packed drawer.  This can
happen regardless of whether the glassine is acid-free or not.

At least one American supplier makes additive-free acid-free
glassine, but two physical steps in its manufacture make it
hygroscopic and translucent: a great deal of beating, and
calendering under high pressure.  I do not know how long a life it
has, but that is irrelevant, in view of its unfortunate physical
effect in a damp environment.

There are many ways to make glassine, whether it is intended for use
with records in an archives, or as an inner wrapper in a cereal box.
(Yes,that is called glassine too.)  Many more ways of manufacturing
glassine were used in the past; all additives seem to have made
early glassines short-lived.

Now, about paper manufacture:  Mr. Farley says glassine is generally
made from wood pulp, "occasionally chemically cooked, though more
usually not." Actually, if the pulp has not been cooked with
chemicals, this means it has been pulped at least partly by
mechanical methods, that is, it is a form of groundwood or
"mechanical pulp"--but groundwood is prized for its opacity, and
this is just the quality the glassine does not need.  Glassine has
to be made from chemical pulp, if it is made from wood fiber.  All
fine paper made from wood pulp has to be "chemically cooked," in
order to separate the fibers and remove the lignin and other
impurities.

Mr. Farley sees a problem with the use of a buffer (alkaline reserve
or pH buffer) in glassine and other papers, and says that "These
buffers however tend to be interventional agents not catalytic,
which means that they take part in the chemical reactions [of
decomposition] rather than just promote them." In fact, although
there are many kinds of buffer, new paper almost invariably uses
calcium carbonate.  It does not take part in the deterioration of
paper; it mops up the byproducts after the reactions have occurred.

He also does not like the idea of the buffer being used up in the
process of protecting the paper from destructive gases; but 400- and
500-year-old papers in good condition were found (by Tim Barrett and
William J. Barrow in separate studies) to contain calcium carbonate,
while those that had suffered from age generally did not.  Five
hundred years of protection is nothing to sneeze at.  If buffered
paper turns out to last only two hundred years, that will still be
very useful.  Poor storage and use conditions, of course, will
shorten the period of protection, but in libraries and archives the
stored materials are not expected to encounter these conditions.

When the calcium carbonate has fully reacted with acidic gases, it
has not disappeared entirely.  A salt, the product of acid-alkali
reaction, is left in its place.  Some of these salts may offer a
degree of protection to the paper too.

Buffering compounds (e.g., calcium carbonate) do not "tarnish"
silver, though a few kinds of photographs are considered to be
vulnerable to the high pH of buffers.  I do not know of any research
that has explored the effect of alkaline buffers on different kinds
of photographic materials.

Ellen McCrady, Editor
Abbey Publications
7105 Geneva Dr.
Austin, TX 78723
512-929-3992
Fax:  512-929-3995

                                  ***
                  Conservation DistList Instance 11:82
                  Distributed: Thursday, April 9, 1998
                       Message Id: cdl-11-82-001
                                  ***
Received on Wednesday, 8 April, 1998

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