Glassine for storage of negatives

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.  The negatives are
stored in a cool dry vault.

Recently he was told by another conservator and a photographer that
the envelopes were detrimental to the collection and should be
replaced.  As they are a small institution, replacement will be an
expensive proposition, but he will do it, if necessary, as it is an
important collection.  Before he invests the money, he would like to
know (1) if the acid free glassine are truly harmful and if so, why?
and (2) is there a physical problem with glassine rather than a
chemical one?

J. Landry
Leaf by Leaf Book and Paper Conservation Services
P.O. Box 1554, Station M
Halifax, N.S. B3J 2Y3 Canada
902-465-2190

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                  Conservation DistList Instance 11:79
                 Distributed: Wednesday, March 25, 1998
                       Message Id: cdl-11-79-011
                                  ***