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Subject: Transcription discs

Transcription discs

From: Gerald D. Gibson <ggib>
Date: Tuesday, December 1, 1998
Andrea Bowes <abowes [at] compusmart__ab__ca> writes

>The archives that I work with has several large collections of glass
>transcription discs from the 40's and 50's and they will be
>reformatting a selection of them soon.  I am unfamiliar with this
>archival record format and would like some further information
>before we proceed with this project.  In particular several discs
>have a white crystal formation over their surface.  What is the
>black layer of the disc made of?  What might the crystals be?
>Finally is there a safe way to remove them?

It is almost certain (the actual discs would have to be examined by
someone experienced with such recordings to be sure) that the "white
crystal formation" on the surface of acetate discs--both glass and
metal based discs--is a mixture of the materials used as plasticizer
for the discs (most commonly castor oil) in reaction with the
moisture in the air.  The means of safely removing is not as easily
answered: The use of Freon with an additive of TF was very
successful, when such was not considered harmful to the environment.
Now, there are a wide variety of practices and formulas that are
claimed to clean effectively, few of which have been evaluated and
tested.

One process that has been written up is that used at Georgia State
University.  It is described in detail in Chris Paton's Selected
Acetate Disc Cleaning Methods (ARSC Journal 28 no. 1, Spring 1997.
pp 1-25).

Gerald D. Gibson
Audio and Moving-Image Preservation Specialist
Preservation Research and Testing Division
Library of Congress
Washington, D.C. 20540-4560
202-707-1055
Fax: 202-707-6449

                                  ***
                  Conservation DistList Instance 12:49
                Distributed: Wednesday, December 2, 1998
                       Message Id: cdl-12-49-003
                                  ***
Received on Tuesday, 1 December, 1998

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