Glassine for storage of negatives

Joe Landry <n1mjbe10 [at] pop1__ns__sympatico__ca> writes

>One of my clients has been using glassine envelopes to house a large
>negative collection in his institution.  The envelopes were
>purchased from a reputable supplier of conservation quality
>materials and the catalogue description says that they are acid free
>and will not react chemically with the negatives.
>...
>Recently he was told by another conservator and a photographer that
>the envelopes were detrimental to the collection and should be
>replaced.

Glassine may be sold as being archival, but that does not mean that
it will be free from causing damage.

It is a material generally made from wood pulp, occasionally
chemically cooked, though more usually not. The source pulp is
mechanically beaten to give it a high degree of hydration, a process
which degenerates the paper fibres. Ethylene glycol and other
additives are then included to increase the translucency and
flexibility of the paper.

In addition to the possibility of the additives causing harm, the
degenerating paper fibre, and the possibility of impurities from the
paper source pose a high potential for damage.

The deterioration by-products of this decomposition are usually
acidic. To get over this problem, manufacturers include a buffer to
regulate the pH level. These buffers however tend to be
interventional agents not catalytic, which means that they take part
in the chemical reactions rather than just promote them. The result
of this is that the more acidity an envelope is exposed to the
higher the rate of the buffer consumption. When a buffer is
completely wasted, degeneration will occur at the normal rate for an
unbuffered glassine. Thus the use of a buffer is a decomposition
delaying tactic, not a permanent stabilising factor. And the
consequent conclusion of this is that stability will reduce upon
ageing through the material's own internal faults as well as through
exposure to any harmful environmental conditions, buffered or not.

This deterioration in all probabilities will affect the material
that it contains.

In the UK, I have seen glassine envelopes marketed with two
descriptions:

    1.  Acid Free* :- this means that it had a neutral pH when it
        was manufactured, it doesn't necessarily mean that it will
        stay that way since there is no indication of the inclusion
        of stabilising additives.

    2.  Buffered Acid Free :- This means that a buffer has been
        included to regulate the pH. Once the buffer is consumed, it
        will degenerate in the normal way as described above.

* One catalogue I have on the desk at the moment, which supplies
"Archival" materials, has the following description:

   "Unbuffered See Thru, Acid-Free Glassine

    Acid free glassine (26 gms) for a variety of conservation
    applications. It is transparent and smooth with a pH of
    approximately 7.0 and is unbuffered. Its light weight makes it
    easy to fold or shape and is excellent for use in situations
    where its transparency is helpful. Available in both rolls and
    sheets"

This passage makes a play on being "unbuffered" and completely
natural, in truth it is unquantifiable and inadvisable to use.

It is also important to note that some buffers that are used in the
production of glassine, are also agents of silver tarnishing. Since
the majority of photographic images are based on silver, any storage
mechanism that contains them must not possess materials that will
cause a reaction.

You will find glassine marketed as "archival", not "Silver Safe",
and I would be extremely surprised if someone showed me a glassine
material which consistently passed a "Silver Safe" test. I would
never recommend the materials use in any archival situation let
alone for photographic storage. 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 11:80
                   Distributed: Friday, April 3, 1998
                       Message Id: cdl-11-80-003
                                  ***