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As Tim indicates, the most reliable way to detect hydrolysis on open reel tapes (1/4" only- it works less well on 1" and really doesn't work on 2") is the "drop" test to see if the tape unspools easily.  Another way is the "sniff" test to see if the tape gives off the odors of "dirty socks", "candle wax" or "Pungent/astringent".    The "sniff" test works better on tapes in hard plastic shippers as the odor dissipates quickly and can be almost undetectable if the tape is stored in a cardboard box. Both these tests are mentioned in the ISO and AES documents on tape handling.

Most pictures of tapes with hydrolysis (sticky shed) show effects after a hydrolyzed tape has been played/spooled.  There are a few, possible, visual indications on an un-played tape but all but one are uncertain.  Some tapes with hydrolysis show a mottled appearance on the oxide surface or a significant lowering of the albedo.  Unfortunately, these visual cues can appear on tapes for other reasons and tapes with mottling or lowered albedo are not, necessarily,  hydrolyzed.  In addition, not all hydrolyzed tapes show these effects.  The only absolutely sure VISUAL indication of hydrolysis on an un-played tape, I am aware of, is a phenomenon referred to as "puddling".  Puddling occurs when a small area on the tape hydrolyses so badly that a small "puddle" of oligomer residue is visible on the tape surface.  Two drawbacks are that this has only been observed on 2" tapes and it happens inside the wraps (so the tape must be unspooled to observe the phenomena).  If a tape has puddling, it is definitely hydrolyzed but it is a very rare effect of hydrolysis so it is pretty useless as a visual test.


Peter Brothers
SPECS BROS., LLC
973-777-5055
[log in to unmask]
Audio and video restoration and re-mastering since 1983

   

-----Original Message-----
From: Association for Recorded Sound Discussion List [mailto:[log in to unmask]] On Behalf Of Tim Gillett
Sent: Tuesday, September 18, 2018 8:05 AM
To: [log in to unmask]
Subject: Re: [ARSCLIST] ISO a photo of "sticky shed"

A much safer way to check is to hold the reel out in front of you like the steering wheel of a car and turn the reel so the tape end starts to unwind under gravity. Even a small amount of stiction should show up as the tape adhering to the next wind.  A non sticking tape should unwind straight down with no sign of adhesion. At least that's the advice I've followed.


Tim Gillett
Perth,
Western Australia

----- Original Message -----
From: "Stewart Adam" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Tuesday, September 18, 2018 7:38 PM
Subject: Re: [ARSCLIST] ISO a photo of "sticky shed"


Here is a video of a ½”eight-track tape that had sticky tape.

https://youtu.be/fgtr_dE8mcE


Stewart Adam
Creative Audio Works LLC
www.creativeaudioworks.com <http://www.creativeaudioworks.com/>
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