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Subject: Zinc plates

Zinc plates

From: Erich J. Kesse <erikess>
Date: Thursday, April 18, 1996
In Conservation DistList instance: 9:71 Scott Williams asked for
additional information regarding the zinc plates described in
DistList instance:  9:70. The following is a response

Q: How are the zinc plates stored--what kind of containers,
packaging, and cabinetry (e.g., wood, painted steel, etc.)

R: Physical housing. The plates were recently "discovered" in old
cigar boxes where they have been stored unopened for the last 15-20
years. The affected areas are most numerous on the plates that have
direct contact with the bottom of the box which has a pH of 3.5.
Under magnification, they appear as spots of corrosion which have
actually dissolved the surface of the plates.  Staff have begun
removing the plates to phased protection in hope of providing a more
stable environment pending further treatment. We are just beginning
investigation of the use of molecular films with future enclosures.
(This investigation began prior to discovery of the plates as we
began to consider protection of our acetate based microform
collections, some of which have begun to have indication of
deterioration.) Enclosed plates, probably grouped into larger custom
made enclosures, will eventually sit on open painted steel shelving
in compact storage--again, plans for final  storage enclosures and
methods are being formulated.

R: Environment:  The plates currently reside in temporary quarters
as renovation of a Special Collections facility proceeds. Current
conditions, while less than ideal, provide an environment with
minimal fluctuation (+/- 5 degrees F and +/- 10% RH) with minimal
filtration and air changes within compact storage. Conditions in the
renovated storage area, a five level stack, will be optimized for
books and paper with zoning specific to each floor and balancing
within zones to compensate for compact shelving. HEPA filtration
will approximate standard targets summarized by Thomson"s Museum
Environment, i.e., slightly less than recommended by the Canadian
Conservation Institute's Environmental Norms for Canadian Museums,
Art Galleries and Archives. The storage conditions of the plates
prior to their arrival at the University is unknown, but it is
assumed that they were not ideal. Some of the wood blocks showed
evidence of mold and mildew, while a few others were split and
warped.

R: General comments. As found, a variety of plates (zinc, copper,
wood, etc.,) were stored together, many dating from the 1880s, some
as late as the 1950s. The majority are mounted on a wood substrate.
Plates will be grouped, for housing, into composite  types.

Q: What is the physical form of the efflorescence ?

R: Appears powdery but hard. Does not brush off. It is unevenly
grouped over the surface of the plate. Not greasy, shiny, glistening
or matt. Not colored, white. Yellow brown stains mark the bottom of
the boxes in contact with the areas of damage. Under magnification
appears granular.

Q: Has the efflorescence been chemically identified? Has its
solubility in water or organic solvents been determined?

R: No. We hope to find literature and experienced treatment
providers before taking any action other than phased protection.

Erich J. Kesse
Preservation Department
Smathers Library
University of Florida

                                  ***
                  Conservation DistList Instance 9:72
                  Distributed: Friday, April 26, 1996
                        Message Id: cdl-9-72-003
                                  ***
Received on Thursday, 18 April, 1996

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