Transcription discs

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?

Andrea, the discs you are referring to are acetate discs.  The
following excerpt was lifted from an article I wrote about the care
and handling of sound recordings.

    **** Moderator's comments:   The complete article is available in
    Conservation OnLine
    <URL:http://palimpsest.stanford.edu/byauth/st-laurent/care.html>

    [...]
    The lifespan of a plastic is largely determined at the
    manufacturing stage. Variables such as basic resin, the
    materials added to the basic resin to alter its properties, the
    lamination of materials with dissimilar properties, and the
    manufacturing process itself, all directly affect the lifespan
    of the plastic.   Post-manufacture environmental factors such as
    storage conditions, temperature, humidity, and handling also
    contribute to the long-term stability of the plastics.

    Acetate Discs
    Prior to the advent of magnetic tape, instantaneous recordings
    were made chiefly on acetate discs.  The chemical makeup of
    these discs, therefore, had to be a compromise between ease of
    engraving and the quality of the recording that resulted.

    Since the 1930s, most blank acetate discs have been manufactured
    with a base, usually aluminum (although glass was used during
    the war years and cardboard for inexpensive home recordings),
    that was coated with nitrocellulose lacquer plasticized with
    castor oil. Because of the lacquer's inherent properties,
    acetate discs are the least stable type of sound recording.

    Continuous shrinkage of the lacquer coating due to the loss of
    the castor oil plasticizer is the primary destructive force. The
    gradual loss of plasticizer causes progressive embrittlement and
    the irreversible loss of sound information.  Because the coating
    is bonded to a core which cannot shrink, internal stresses
    result, which in turn cause cracking and peeling of the coating.

    Nitrocellulose acetate decomposes continuously and over time
    reacts with water vapour or oxygen to produce acids that act as
    a catalyst for several other chemical reactions such as the
    release of palmitic acid, a white waxy substance.  As with most
    chemical reactions, these reactions are accelerated with
    elevated temperature and humidity levels.
    [...]

You will need to find an audio conservator to do the transfers. If
you cannot, then a recording studio capable of playing 78s properly
must be found, i.e. a studio equipped with: record cleaning
equipment with an operator trained and experienced in cleaning
fragile discs, a turntable which can play 78s, a 12" tonearm (if you
have 16" records), preamplifier with varying playback equalization
(bypassing RIAA playback EQ), a large range of styli of various
sizes and shapes and an audio engineer who is sensitive to the era's
recording techniques, technology and sound.  The latter is
particularly important if the machine on which the recording was
made is not known; the setting of the playback EQ must be done by
ear.  If an experienced audio engineer cannot be found, a dub can be
made with no playback EQ whatsoever until an experienced conservator
can be found to do the work.  Even if your records are mono, make
sure that the work is done in stereo, as quite often there will be
subtle, and sometimes not so subtle, differences between the two
sides of the groove.

Peruse the ARSC (Association for Recorded Sound Collections)
Membership Directory for names of people who might be able to do the
work.  The ARSC Membership Directory should be available on
Interlibrary loan.

As for cleaning acetate discs (again from my article):

    [...]
    General

    The Canadian Conservation Institute (CCI) recommends the use of
    nonionic, ethylene oxide condensates surfactants to clean sound
    recordings.  The CCI does not foresee long-term problems
    associated with the use of nonionic surfactants such as
    Tergitol.  Tergitol 15-S-3 is an oil soluble surfactant and
    15-S-9 is a water soluble surfactant.  Combined they remove a
    wide range of dirt and greases and can safely be used on sound
    recordings.  Use 0.25 part of Tergitol 15-S-3 and 0.25 parts of
    Tergitol 15-S-9 per 100 parts of distilled water.  (These
    products are available in small quantities from TALAS (Division
    of Technical Library Service Inc) 213 West 35th Street, New
    York, N.Y. 212-465-8722.)  The recording must then be rinsed
    thoroughly with distilled water to eliminate any trace of
    detergent residue.

    Keep an airgun handy to blow off light surface dust.

    Grooved discs

    Grooved discs are best cleaned using a record cleaning machine
    such as the Keith Monks, VPI, Nitty Gritty using 0.25 part of
    Tergitol 15-S-3 and 0.25 parts of Tergitol 15-S-9 per 100 parts
    of distilled water.  These machines allow for an even dispersion
    of fluid and can then vacuum the liquid leaving a clean, dry
    surface.  The discs must then be rinsed thoroughly with
    distilled water and vacuumed dry to eliminate any trace of
    detergent residue.  Records should be cleaned before each
    playback.

    Clean acetate discs showing signs of palmitic acid deposits
    (white greasy substance on acetate disc surface) as if cleaning
    LPs, except add 1 part ammonia per 100 to the Tergitol cleaning
    solution.  Do not use ammonia on shellac based discs.

    [...]

You may also want to consult the ARSC Journal  Volume 28, No. 1
(Spring 1997) for a good article on cleaning acetate discs.

Gilles St-Laurent
Music Division
National Library of Canada

                                  ***
                  Conservation DistList Instance 12:49
                Distributed: Wednesday, December 2, 1998
                       Message Id: cdl-12-49-005
                                  ***