Nitrate negatives

We have been rehousing our collection of 1000 Roger Parry cellulose
nitrate negatives in preparation for freezer storage. Approximately
two months ago, each negative was placed in a paper envelope (Apollo
Buffered Balanced Seam Envelopes from Light Impressions) and stored
inside Drop-Front Boxes (Lig-Free, Buffered) in our
climate-controlled conservation lab.

The second step of sealing the negatives in vapor-seal envelopes and
freezing them was postponed while waiting for labels. In examining
the negatives this week, it was noticed that approximately 10 of the
more-deteriorated negatives now have the words of the watermark
("Buffered Apollo...") "written" on them in silver mirroring. In
most cases, the mirroring is greater in the letters of the
watermark, in a few it is the other way around. It seems as though a
general pattern of overall silver mirroring concentrated in the
center of each neg. was already present on these negatives, as well
as a number of others.

Has anyone seen this before? We are not clear as to whether the
buffering of the envelope has caused the problem, or protected the
negative in all areas except where the watermark is.  Also, we are
wondering whether freezing them will halt any further damage in this
manner? We are also considering changing the housing to non-buffered
envelopes.  Any ideas would be appreciated.

Heida Shoemaker
SFMOMA Conservation

                                  ***
                  Conservation DistList Instance 12:26
                Distributed: Tuesday, September 15, 1998
                       Message Id: cdl-12-26-013
                                  ***