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Subject: Glassine for storage of negatives

Glassine for storage of negatives

From: Jonathan S. Farley <j.farley>
Date: Wednesday, April 15, 1998
I note Ellen McCrady's response to my description of some of the
problems of glassine, and although she agrees that the use of the
material should be discouraged, she disagrees with my response
because in her words it is inaccurate.

As far as I can see Ms. McCradey's argument is divided into three
points:

    1.  The processes I describe are not illustrated in the
        ANSI(1991) standard or Wilhelm's admirable work, and
        therefore presumably for her, do not exist.

    2.  Glassine is not manufactured in the way I described.

    3.  I disagree with the use of buffers.

I will answer these points in the above order, I do not wish to
engage in an internet  "flame war", nor do I wish to trespass on
Walter's good nature, therefore this will be my last open response
on the matter.

    1.  It is not in ANSI

The ANSI standard is restricted by space to giving what it perceives
to be the major cause for the discouragement of this material
amongst a great deal of other information it has to supply in a very
short space. It states simply that under damp conditions it will
imbed itself into the emulsion of the photograph. This is quite
correct as far as it goes, however since most archives do not
envisage ever having a damp problem within their storage situations,
the use of glassine is still widely decided upon hence the original
query. Because of this I chose to illustrate a further problem with
glassine which I hoped would be more persuasive in discouraging its
us.

Because ANSI does not illustrate the problem I have described, does
not mean that it does not exist, it simply means that it is not
illustrated in ANSI.

Further to this point, I have continually read on this list, and
heard at conferences the same question: "*why?*". There are many
books on photographic preservation which state simply that the use
of glassine is discouraged, of which many do not give the source of
this argument, (for example Siegfried Rempel's "The Care of
Photographs" page 131) and those that do give references when
checked only point to other works which make the same statement. It
is very difficult to find references to adequate chemical reasoning
for this discouragement and considering the response I have had from
students world wide, I am not the only person to perceive this
problem.

Although the ANSI standard may be considered as a primary source for
referencing purposes, its conclusions are based on prior
publications and experimental information, and not all of this
information has been repeated in the final version. For this reason
it is sometimes necessary to avoid quoting by rote as Ms. McCrady
suggests in her statement:

   "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"

If one has experimental information one wishes to broadcast, one
must be allowed to do so without having others dictate that it is
imagined because of its absence from the standard. This is an
extremely important point when you consider that experimentation
does not cease the moment a standard is produced.

With regard to Wilhelm's book, there is more to glassine than Ms.
McCrady`s vague reference to page 467 (a portion of which I will
give later on). Most of the work of Wilhelm (pp 375, 440, 467,
502-504) illustrates the chemical nature and manufacturing processes
I described contrary to McCrady's affirmation that it does not. In
addition, Wilhelm's work is widely based upon the conclusions of
Eugene Ostroff the first person to specify a problem with glassine
(and consequently the father of all glassine references, he also sat
on the original ANSI panel by the way):

   "Another short lived paper, frequently used for photographic
    envelopes, is glassine paper, which during manufacture is more
    "hydrated" than other papers. This results in a somewhat
    degraded fibre. Various additives such as plasticizers for
    flexibility are used to impart certain optical (transparency),
    mechanical and chemical characteristics. These with time,
    volatilize or leach out and can have a detrimental effect on
    image stability on adjacent photographs"

        ("Preservation of Photographs", article in The Photographic
        Journal, Vol 107 No 10 pp 309-314 of the Royal Photographic
        Society)

The "hydrated" paper fibres as described by Wilhelm on page 467 and
by Ostroff above are seriously degraded. They are short, brittle
(hence the inclusion of plasticisers) and prone to rapid decay. The
by-products of this decay are invariably acidic, hence the inclusion
in some glassines (though not all) of buffers.

    2.  Manufacture

Ms. McCrady does not agree with my statement that machine ground
wood pulp is used for the manufacture of glassine because mechanical
pulp is prized for its opacity. Firstly to quote Wilhelm's now
famous page (467):

   "Glassine paper is a thin, very smooth translucent paper used
    extensively for negative enclosures and sometimes for
    interleaving purposes. Glassine is made from wood pulps that
    have been mechanically beaten to have a high degree of
    hydration, a process which degrades the fibres"

Wilhelm does not give chemical cooking of the pulp in his
description as a main criteria for the manufacture of glassine
because it is not a necessary process.  It is possible to illustrate
this point by performing a simple experiment. Firstly acquire a
sheet of machine ground wood pulp "Bank" or "Bond" grade paper.
Place this upon a sheet of silicone release paper and with your
finger, rub some butter into it. The paper, which was perfectly
opaque at first,  will become as transparent as glassine through the
action of a lipid transparentizer.

Lipids were the main transparentizer for food hygiene glassine packages
such as Ms.McCrady mentions in her reply until the the early 1980s
when they were replaced by a modified paraffin wax. You can
illustrate this as well by performing the same test using
Renaissance microcrystalline wax applied to the paper with a
household iron through another layer of silicone release paper. As
you will see transparentizers have an astounding effect on opaque
papers, ethylene glycol (the standard "Archival" transparentizer) not
being any less effective. You can see from this that chemical
cooking is not a necessary process for the manufacture of glassine.

This can be further confirmed by acquiring as many samples of
different glassines as you can and subjecting them to a
Phloroglucinol "Lignin" test. Machine wood pulps will give a strong
reaction, whereas chemical wood pulps will give a much paler
response since the chemical cooking removes a great deal (though not
all) lignin from the paper. Of the 13 different envelope samples I
have before me at present, 9 have given a strong reaction to the
phloroglucinol test.

Ms. McCrady illustrates an American manufacturer who produces a
glassine that is additive free, acid free, and whose transparency is
produced by a great deal of beating and calendering under high
pressure. Unfortunately it is this great deal of beating and
calendering which produces the degraded "hydrated" paper fibre that
Wilhelm describes above. As I stated in my previous mailing, this
material may be acid free when it leaves the manufacturer, it will
not remain so, so I fear that this argument has only served to
reinforce my point.

    3.  Alkaline Buffers

Ms. McCrady also takes umbrage at what she perceives to be my
objection to the use of buffers in all papers. This is once again a
misinterpretation. I am not objecting to the use of buffers at all,
I am merely stating that with the materials involved in the
manufacture of glassine, the inclusion of a buffer has no
perceivable effect, since the acidity produced by the
autodegradation of the paper fibre, the volatilizing plasticisers
and transparentizers, not to mention the possible effects of pollution
will rapidly reduce a buffer to ineffectual unless there is a high
reserve, which it is not possible to have. To quote Dr. Ware (who I
believe is on this list):

   "Photograph conservators will be familiar with the consensus,
    expressed in publications specifying the currently recommended
    practice that wrapping materials for photographs should be
    un-buffered, WITHOUT ANY ADDITIONAL 'ALKALINE RESERVE' of
    calcium carbonate. The view that alkaline buffer is deleterious
    to photographs has led to the development and wide adoption of
    the well known paper Atlantis Silver Safe Photostore, as an
    unbuffered wrapping paper especially for photograph
    conservation"

        (Quantifying the Vulnerability of Photogenic Drawings:
        Proceedings from the Copenhagen Conference, May 1995)

I also recommend reading Wilhelm Pages 471-472 for more information.

I believe that this quotation also dispenses with Ms McCrady's
statement that Calcium Carbonate does not effect silver images since
Silver-Safe Photostore would have been developed with such a buffer
if as she suggests it does not "tarnish" or by its interactions
result in "tarnishing".

The one unsupportable observation that I did make was that a buffer
in glassine would be rapidly wasted unless the buffer itself was a
catalytic agent rather than an interventional one. Had the included
buffers been catalytic, glassine might just have had one argument
for it even though this would still have been outweighed by the
arguments against.

I am afraid that Ms. McCrady misunderstood this point as well.

Other points Ms. McCrady made were that  Wm. Barrow and Tim Barrett
(in separate studies) found 400-500 year old paper with a calcium
carbonate buffer, while those that suffered from age generally did
not posses any. This argument is ineffectual since firstly the paper
stock was exceedingly pure, and consequently had very little, or no
inherent instabilities for the buffer to work on.  This is
reinforced by the fact that the paper which had "suffered from age"
is still in existence today (500 years later) without the assistance
of a buffer. The argument consequently can not be used as a
correlation with mechanical and chemical wood pulp which both posses
inherent impurities that a buffer would necessarily have to work
upon.

She also used as an illustration the fact that :

   "When 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"

Unfortunately this is not a forcible argument either. A certain
portion of calcium carbonate (about 0.02%) will remain no matter
what materials are thrown at it. It will not react with anything, I
am not sure why, perhaps a chemist can explain. More importantly,
the salts of reaction can not be used as a basis for argument since
as the product of an acid-alkali reaction, they are:

    1.  nearly always neutral pH
    2.  have a stable valency within the structure of the paper and
        so will not react any further

and lastly

    3.  the exact nature of the salts is unquantifiable since
        internal and external factors will make the salt composition
        too variable to perform an accurate analysis.

For all of these reasons,  I would still discourage the use of
buffered papers where photographs are concerned since it is better
to know what you are not getting than not to know what you are
getting.

I think that the majority of conservators and photographic chemists
would agree with me on that point.

I hope that this will close the matter. Regards.

Jonathan S Farley
Senior Conservator
Royal Botanic Gardens, Kew
Richmond, Surrey TW9 3AE
ENGLAND
+44 181 332 5419
Fax: +44 181 332 5278

                                  ***
                  Conservation DistList Instance 11:84
                 Distributed: Wednesday, April 15, 1998
                       Message Id: cdl-11-84-003
                                  ***
Received on Wednesday, 15 April, 1998

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