Of possible interest, posts copied from the Ampex list:

Message: 4
Date: Wed, 09 Sep 2015 06:06:46 -0400
From: Mike Rivers <[log in to unmask]>
To: [log in to unmask]
Subject: [AMPEX] New Method For Evaluating Tape Playability
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A group of scientists have come up with a procedure for evaluating a
tape on the reel to determine if it needs baking.

From the article:

You might ask why not automatically bake the tapes, but no one has 
enough time, explains Stephen L. Morgan, a chemist at the University of 
South Carolina and coauthor of the new work. Our goal was to develop an 
easy, noninvasive method to identify the tapes that are in the most 
danger, so that they can be prioritized for digitization.

In the new work, Morgan, Eric M. Breitung of the Library of Congress, 
and collaborators first randomly selected 133 quarter-inch audio tapes 
from a Library of Congress collection acquired in the 1970s, 1980s and 
1990s. They then used attenuated total-reflection Fourier transform 
infrared spectroscopy to analyze small sections of the tapes. They found 
that the presence of spectral peaks characteristic of polyester-urethane 
degradation products, among others, could be used to identify the tapes 
that were nonplayable which the researchers confirmed by observing them 
on a headless reel-to-reel tape player with 92% accuracy. These would be 
candidates for baking and prompt digitization.

More here from Chemical Engineering News:

Message: 6
Date: Wed, 09 Sep 2015 13:59:57 -0400
From: Scott Dorsey <[log in to unmask]>
To: [log in to unmask]
Subject: Re: [AMPEX] New Method For Evaluating Tape Playability
Message-ID: <[log in to unmask]>
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The good things about this:

1. It identifies some compounds (if only by absorption spectrum) that 
  indicate binder breakdown which can be more carefully analyzed in the

2. It indicates problems with the tape binder itself rather than just the
  backcoating, providing additional validation to the theory that it is
  the binder itself breaking down.

The bad things about it:

1. The test itself is not practical for spot-checking tape libraries.  The
  reel has to be pulled and unreeled for the surface to be analyzed.  What
  is needed is a swab that can be wiped on the outer edge of the tape wind
  and then analyzed either in a machine or by eye.

2. The overlap between tests of playable and unplayable tape is great, so
  this test will either produce a lot of false positives or false negatives
  depending on how it's calibrated.

I'm not saying this isn't useful research, I'm just saying that as a
production test this is of limited use. 

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