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Subject: Deterioration of glass negatives

Deterioration of glass negatives

From: Andrea Schwarz <ea_schwarz>
Date: Thursday, November 16, 2000
Eli Echols <eaechols [at] newchurch__edu> writes

>At the Raymond and Mildred Pitcairn Archives in Bryn Athyn,
>Pennsylvania, we have a collection of about 4000 Glass Negatives. We
>are only just beginning to address their preservation appropriately,
>and in doing so I have noticed that many of them smell pretty
>strongly of vinegar.

I came across this phenomena as well during my work on the glass
collection of the Swiss National Museum in Zurich. A few heavily
corroded vessel glasses smelled of vinegar, too.

Qualitative analysis of the composition of three glasses from the
collection (unfortunately not one of the strongly smelling ones)
showed that one cause for their sensitivity towards poor
environmental conditions, especially high relative humidity, was
their unstable composition. Moreover, measurements of the air in the
store revealed high levels of formaldehyde, which were caused by
chipboards used in the store. Qualitative analysis of the glass
corrosion products using x-ray diffraction and FT-IR-Spectroscopy
revealed sodium formate and potassium sulphate.

As you do not mention the environmental conditions in the
store/museum, I wonder if there could be a reaction  between the
unstable glasses alkaline surface and carbonyl pollutants in the
air? This reaction only occurs at a high relative humidity in the
storage. For further information about my work, I would be glad to
help you,

Andrea Schwarz

                  Conservation DistList Instance 14:29
                 Distributed: Monday, November 20, 2000
                       Message Id: cdl-14-29-002
Received on Thursday, 16 November, 2000

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