RE: [AV Media Matters] acetate tape and plasticizer crystals

[Peter Brothers <lists@specsbros.com>]

The clear/white crystalline residue could be a number of things including
plasticizer, surfactant or lubricant.  It could also be a variety of
chemicals used in manufacture that were inadequately leached out of the tape
before distribution.

Cleaning off this sort of debris is usually done using a low-abrasive,
non-dusting, long-fiber wiping tissue such as Pellon.  When wiping the
surface of the tape, one must be very careful that the debris does not build
up on the wiping tissues and scratch the tape surface.

Burnishing (sometimes called "blading") should not be used on decaying
acetate-based tapes as the tapes can be brittle.  "Baking" to stabilize the
hydrolyzed recording layer should NEVER be used on this type of tape as the
heat process can be extremely damaging to the acetate base.

If the recording layer has been compromised due to the long-term exposure to
humid conditions, there are a number of alternate ways to stabilize the
binder without damaging the acetate base.  These methods, of course, require
specialized equipment and are quite time consuming.

After the tapes have been wiped clean, if the tapes bind or squeal during
playback, you might want to try replacing any fixed posts on your machines
with rollers and treating the heads to reduce friction.  If that doesn't
work or you are uncomfortable about trying to handle the tapes yourself,
well, there are always professional restoration companies.

Peter Brothers
President
SPECS BROS., LLC
peter@specsbros.com
web-site: http://www.specsbros.com
TAPE RESTORATION AND DISASTER RECOVERY
SINCE 1983

-----Original Message-----
From: nathan_georgitis@hotmail.com [mailto:nathan_georgitis@hotmail.com]
Sent: Thursday, April 06, 2000 3:51 PM
To: AV-Media-Matters@topica.com
Subject: [AV Media Matters] acetate tape and plasticizer crystals

Greetings from a lurker.

I recently looked at some cellulose-acetate audio tapes from the mid-1960s.
The oxide side of many of these tapes were besprinkled with spots- seemingly
crystalline, sometimes small and sometimes larger, generally clear or
whitish in color. In The Preservation of Recorded Sound Materials (ARSC,
Vol. 23.2), St. Laurent writes that the plasticizer additives in the
cellulose acetate evaporate and crystallize over time.

He doesn't describe the physical manifestation of this degradation, though.
Or say how greatly it affects tape to head contact or playback.

I'd like to know if anyone's observed anything similar and what strategies
have been employed to deal with the problem.

How does one clean magnetic tape, aside from vacuuming surface contaminants?

These tapes have been subjected to very humid conditions at times, though
the housing doesn't show any signs of water damage or biological
contamination.

Thanks in advance,
Nathan Georgitis
Graduate Student
Archives Management Program
Simmons College G.S.L.I.S.