At some point, this tape was played on a 1/4-track machine that injected hum onto the left channel. Here’s what the magnetic viewer showed:

At the very top we can see a remnant of the left channel material, then the 120-Hz bars (62.5 mil spacing), then the remainder of the left channel material. In the middle is the guard band and at the bottom, the right channel.

Using a specially manufactured (by JRF Magnetics) assembly that contains a 4-channel 8-track head with a continuously variable height adjustment, we were able to lower the track one head to the middle of the good portion of the left channel. With that height positioning, track five’s head was well into the right channel, so we got a good transfer without the hum.

We believe this hum was written by the record head due to a malfunction in the recorder rather than an intentional erasure. If there had been an erasure, more of the left channel would have been erased and there would be a guard band between hum bars and the left channel audio as almost all erase heads were wider than the audio heads.

This type of damage is all too common using old consumer tape machines for playing tapes. I had an old junker machine in the 1960s that did this once to a tape. Unfortunately, it was also a quarter-track recording, so it was gone.

The magnetic record is fragile.

We continue to receive poorly wound tapes and are able to play them successfully. So why the quandary now? The reason is that I read portions of another Bharat Bhushan book, Mechanics and Reliability of Flexible Magnetic Media, 2nd Edition, New York, Springer, 2000. Referring to several research papers he makes a compelling case that tapes should be rewound annually if subject to storage environment fluctuations and every 3.5 years if kept in a climate controlled storage area.

If we think about the two types of stresses on each layer in the pack, this becomes more clear. There are “hoop stress” which is the circumferential stress in that individual layer and the “radial stress” which is the stress in the direction of the centre hub.

Low interlayer pressures, which predispose the tape stack to ILS [Interlayer Slip], are created as follows: the winding of successive layers of tape onto a reel increases the radial compressive stresses in the wraps of tape at and near the hub. The continued inward radial deflection of the hub converts the circumferential tensile strain in the tape, originally caused by winding, to a compressive strain….The tape, hub, and winding parameters sufficient to obtain this condition can be determined using [the complex] analysis presented in Chapter 5. A highly compressible hub, high outer-wrap winding tension, low inner-wrap winding tension, the length of tape stored on a reel, and the entrapment of air during high-speed winding are strong contributors to low interlayer pressure

The interlayer pressure from winding is further reduced by temperature and humidity cycling and/or storage….The interlayer pressure can be reduced when the wound tape is subjected to a temperature of humidity change, and is dependent on the relative value of the coefficients of thermal and hygroscopic expansion of the hub and the tape. This effect is aggravated not only by the magnitude of this differential mismatch, but also by the mismatch in the tape’s radial and circumferential coefficients of thermal and hygroscopic expansion.

Bhushan also indicates that spoking can be triggered by impact forces to the tape reel. (Dropping it?)

One of the very interesting things which is discussed is that a tapered winding tension may produce a more archival tape pack than a constant tension winding tension. This raises many questions concerning current archival practices.

I suspect that more discussion of this will occur. Please leave your comments.

Peter Brothers left a lengthy response to this post in the Society of American Archivists list which I am reproducing here. I agree with him on all the major points, but I think Bhushan’s work was done in the late 1980s or early 1990s on single-reel data cartridges as part of the IBM proprietary tape systems like the 3480 (5.5-inch-square cartridge) and 3490 (same size as 3480). These are 1/2-inch wide serpentine recorded tapes and are the forerunner of the LTO tape.

=======================================

Date:      Tue, 15 Feb 2011 13:30:18 -0500
From:     Peter Brothers <peter (at)  specsbros (dot) com>
To:          Archives & Archivists (A&A) List <archives (at) forums (dot) archivists (dot) org>
Subject: RE: [archives] VHS Collections

Hello Richard:

I agree with you about not winding/rewinding tapes in storage unless there
is a compelling reason to do so. There is a significant chance of damaging
tape during the process. We wind and rewind tapes before transfer but that
is to check the tape condition, clean the tape for optimal signal response
and is done on special equipment.

In the Blog post you asked for comments, so here goes-

I can understand the findings you quoted from Bhushan as they might relate
to large reel-to reel tape. I was indicating in my earlier e-mail that
there are no studies I’ve seen that show a net benefit to periodically
exercising (winding) VHS tapes.

I don’t know what type of data tapes Bhushan was testing but if we compare
2″ video tapes (similar to the early data tapes we processed for the
government that exhibited the problems he highlights) to VHS, there are a
significant number of differences that make the conditions he was testing
much less relevant for VHS than for large reel-to-reel.

In the section you quoted from Bhushan’s study, he was suggesting exercising
tapes to counter the loosening of the tape pack due to tension stresses, hub
compression and expansion and contraction of the tape due to environmental
changes in storage. VHS is wound at a much lower tension than 2″ data tape
so that variations in the winding tension are not as critical to the tape
pack in storage. Similarly, some 2″ data tape we processed had rubber
wrapping around the hub that allowed for hub compression. This wrapping is
not used on VHS so hub compression is not critical. Finally, the main
problem we have seen with loose packs is due to expansion and contraction of
the tape that, as Bhushan points out, is due to heat and moisture changes in
the environment. The primary vector for thermal and hygroscopic
expansion/contraction is in the thickness of the tape. VHS is approximately
1/3 the thickness of 2″ data tape so there is significantly less material
per strand of tape to contract. In addition Bhushan indicates the
expansion/contraction effects are related to the circumference and radius of
the tape pack. A standard 120 minute VHS is 812 feet long and is on a 3 1/2
inch reel. A standard 60 minute 2″ video (similar to the 2″ data) is 4,950
feet long and is on a 12 1/2 inch reel. Considering the thickness, width
and length of the tape, there is nearly 72 times as much tape material on a
2″ 60 minute reel to be affected by expansion/contraction than on a 120
minute VHS and the 2″ reel is nearly 4 times the diameter of the VHS.
Expansion/contraction effects that might cause serious damage to 2″ tapes
are negligible on VHS.

Over the last 27+ years we have processed over 350,000 tapes at our facility
and we have definitely seen the negative effects of loose tape packs from
expansion/contraction during storage on large reel formats (2″ video, 1/4″
audio, etc.). Where these effects are extreme and allowed to remain
uncorrected, they can result in unrecoverable damage to the tape in
long-term storage. On the other hand, unless a tape has been exposed to
flood, fire or machine malfunction; we have never seen a VHS or other small
reel cassette with a hub lock that has suffered significantly from
expansion/contraction in storage.

All that being said, I do not believe there is any net benefit to
periodically winding and rewinding VHS tapes in storage. There may be some
benefit to exercising large format/large reel tapes but the practice, as you
pointed out, exposes the tapes to possible machine damage.

Peter Brothers
SPECS BROS., LLC
973-777-5055
peter (at)  specsbros (dot) com

=======================================

Doug Nishimura of the Image Permanence Institute of the Rochester Institute of Technology responded with a recollection of discussions “back in the day” concerning the issue of winding tape and stresses–this more from his experience working with film than tape, but some of the same basics should apply. I wanted to include the point about polymer flow as I do not think that Bhushan addressed that in the studies (but I could be wrong) and it presents yet another property of polymers to consider when deciding how to approach the issue.

I am still open to further discussions on this which can be appended here.

=======================================

Date:      Tue, 15 Feb 2011 14:52:18 -0500
From:     D NISHIMURA <dwnpph (at) rit (dot) edu>
To:          Archives & Archivists (A&A) List <archives (at) forums (dot) archivists (dot) org>
Subject: RE: [archives] VHS Collections

Back in the 1980s there was a rather circular concern (which came first?). If left alone, tape packs would loosen and therefore periodic winding was considered to be good to “retension” the pack and prevent damage due to a loose pack. I don’t recall ever looking for test data on the problem, but a number of tape manufacturers raised the issue. On the other side was polymer flow that said that if you put a polymer under constant stress, the polymer molecules will move (relative to each other) so as to remove the stress (and this is the problem that we have with films wound on small spools). (This is also known as creep or stress-relaxation in materials science, although technically, creep is more general and stress-relaxation applies to materials with constant strain and not constant load.) The demonstration was to hang a ribbon of some polymer by one end and hang a weight from the other end. If you left it over time, the ribbon would stretch and would get longer (under constant load.) So if you “retension” a tape and leave it, the polymer molecules should move relative to each other so as to remove the stress. In theory, the tape stretches and the tape pack gets loose again (requiring retentioning) and so and so on.

That then caused the whole question about whether it was better to leave the tape (and potentially cause damage to the tape) or retension periodically and risk destroying the magnetic information through tape stretching.

The recent experience: A client project generated about 70 GB of files so hard-drive delivery made sense–especially since I had two gently used Western Digital Passport 80 GB drives sitting on the shelf. There would be no infant mortality here. The client (on one continent) and the producer (on another continent) were both to receive copies. I shipped them off and the producer (on the same continent as I) received his copy first and mentioned to the client he couldn’t read it on his Mac. The client had told me he was sure that the Mac would read NTFS, so based on my conversation with Eric, I decided, with client approval, to send NTFS. A few days later, the client received his copy and is pleased with the files and was able to open them without a hitch on his Mac.

As of this writing, the issue of the producer’s disk is still up in the air. I have offered to take it back, reformat it as FAT32, reload the files with MD5 checksums, verify the checksums, and return the drive to him. I think the producer is looking for a Mac utility that will permit reading the disk as-is. I hope so, less work here, but still I’m willing to undertake this to maintain client satisfaction.

In the meantime, I was searching for an easy way to format a drive larger than 32 GB in FAT32 which is locked out by design in Windows XP. It turns out that there is a DOS-box utility, FAT32FORMAT, that works like a charm. If the drives are combo USB/FireWire, using the Sound Devices 722 to format them would be a choice, but for USB-only drives, that is not an available option. PLEASE be careful as this utility will destroy all data on the disk. Use it with care.

After posting the above, the producer gave up trying to read the disk. I reformatted it FAT32, reloaded it, sent it back to him and he was happy.

For several years, we have been discussing the differences between Sticky Shed Syndrome (SSS) and Loss of Lubricant (LoL). It appears from my latest research (presented at the 2006 Audio Engineering Society’s 121st Convention in San Francisco in October) that LoL does not really factor into the equation for most tapes and that an overarching failure mode is Soft Binder Syndrome, or SBS. Sticky Shed Syndrome appears to be a subset of SBS.

The classic recommendation for tapes suffering from SSS is to bake them and, for now, the continued recommendation is to bake tapes for which baking works. These include:
Agfa (pre-1990): PEM 468, PEM 469
Ampex/Quantegy (1970s-1980s): 406, 407, 456, 457
Note: Recent reports indicate that these problems may exist in tapes made in the 1990s
and later, even under the Quantegy name.
Audiotape/Capitol (early 1980s): Q15
Note: This tape may or may not respond to baking. Some tests will be conducted soon.
Scotch/3M: 226, 227, 806, 807, 808, 809
Scotch 250 has also exhibited some tendency towards SSS

For a current list of degrading analog tapes, click here.

Baking (or incubation) times are getting longer, and 12 hours is not uncommon for 1/4-inch wide tapes. Some tapes need to be re-baked after partial unwinding due to centre-of-reel increased inter-layer pressures. There is some discussion of pressures and tensions here.
If these are squealing and leaving significant deposits, they should be baked (at your own risk). The now-expired Ampex patent for baking tapes can be found here. Almost all SSS tapes are back-coated tapes and the interaction between the magnetic coating and the back coating may be part of the problem.

Tapes which squeal (and generally leave less of a deposit and are generally not back coated) appear to be suffering from SBS. SBS appears to be a change in the glass transition temperature of the magnetic coating. The glass transition temperature (Tg) is the point where the plastic turns from smooth to rubbery. If the Tg falls below the temperature of the head (slightly above room temperature due to friction and player heat dissipation) then the tape is likely to squeal. Small deposits of magnetic coating on the head or other fixed surfaces will exacerbate the squealing. Of course, the drop in Tg is not an isolated phenomenon, but rather a symptom of serious binder degradation.
Lowering the temperature of the playback environment will permit successful playback of some tapes suffering from SBS. We currently have a dedicated refrigerator with both a reel and cassette machine inside. Others have reported success in using an outside balcony during cool/dry weather.

Baking a tape that generally exhibits SBS (and not SSS) may exacerbate the condition and it is not recommended to bake suspected SBS tapes.

Tapes which appear to be suffering from SBS include:
Scotch/3M: 175 and Melody 169 (a seconds brand of Scotch)
Sony: PR-150
Pyral: (type numbers unknown for this French tape)

For a current list of degrading analog tapes, click here.

We have seen cassette tapes also suffering from SBS. These were generally made from pancakes and the tape type is unknown.
As an alternate, you might try Marie O’Connell’s tried and true method shown here. In this case, it appears that the isopropyl alcohol is acting both as a lubricant and as a coolant, and may be also acting as a solvent to remove or inhibit deposits from the tape onto the fixed surfaces.

I recently came across a 3-inch reel of acetate tape, not in its original box, that showed the following pattern in the box. This tape was recorded in Fall of 1964 and the photo was taken on October 2006, 42 years later. The tape played well, considering it was originally recorded at 1.88 (1-7/8) in/s.

All of the outgassed material that was absorbed by the cardboard was no longer free to degrade the tape.

One of the interesting things about this particular tape was it had been recently wound on a constant-tension professional machine prior to shipping to me.

We think that the entire tape had not been re-wound, allowing the higher tension wind to compress the inner core slightly, causing this cinching. After transferring the tape (which didn’t show much ill effect for its cinching), we still found it difficult to get the tape to wind smoothly on the reel.

Therefore, our current suggestion is if you find a tape like this, do not rewind it and attempt to clear up the cinching unless you are also ready to transfer the tape, as there are no guarantees that it can be wound better after unwinding.

Please see this post for an update (2008-02-15).

For a current list of degrading analog tapes, click here.

There are multiple modes of degradation and it depends on the type of tape.

Acetate Tape

• Degrades through drying out (hydration has helped in some cases)
• Breakdown of the base through “vinegar syndrome” and possibly leading to total decompostion (although that has not been seen for tapes on any large scale)
• Damage from heat
• Damage from mold/fungus
• Loss of Lubricant is probably rare in acetate tapes. Few examples of it have been found.
• Freezing acetate tape (especially) is considered bad as many of the formulations included fatty-acid lubricants. Remember, this was from the 1940s and 1950s and one of the best lubricants of the era was sperm oil.

Polyester tape

• Binder hydrolysis (or sticky shed syndrome [SSS]) is the largest challenge faced with tapes from the 1970s-1990s. This can be partially reversed through incubation or heat treatment. While this link may not be complete, it is a great introduction.
• Loss of Lubricant (LoL) can be severe and can possibly be combined with binder hydroysis.
• Freezing is also not recommended for polyester tapes due to the potential of that tape also containing fatty-acid lubricants.

Obviously all tapes can suffer from mechanical damage and poor winds.

I expect to be discussing aspects of this in greater depth, but it is a complex subject and contradictory reports have been generated.

This checklist is not a complete guideline. It contains only those items that experience and testing show will have an immediate or severe effect on magnetic tape. Failure to adhere to the items on this list may cause premature loss or deterioration of magnetic tapes and should be considered misuse of the medium. These are minimum handling requirements that summarize good practices.

DO LIST

1. Familiarize yourself with proper techniques for the care and handling of magnetic tapes.
2. Learn and use correct procedures for operating equipment.
3. Handle tapes gently.
4. Keep tapes in protective cases when not in use.
5. Keep tapes vertical when not in use.
6. Make sure machine alignment is correct before use.
7. Clean tapes before use if they show any evidence of dirt or contamination.
   Caution Mold/Fungus can be hazardous to your health-wear a mask.
8. Ensure that the tape is properly seated in the machine before use.
9. Wind tape at low speed (library wind) entirely onto one reel after use.
10. Leave analog audio tapes on the take-up reel after use (tails out).
11. Secure tape ends on open reel tapes
12. Package tapes adequately for protection before shipment or transport.
13. Use only new tapes when recording a tape for long-term storage.
14. Break off or activate the record protection tab of cassettes.
15. Inspect tapes for damage or contamination before use.
16. Clean tapes before use if they show evidence of dirt or contamination.
17. Seek experienced help as soon as possible in the case of a disaster.
18. Protect both tapes and machinery from dust and debris
19. Keep tapes in as stable and uniform an environment as possible.
20. Acclimatize tapes before use if they are hot or cold.
21. Store tape in a cool and dry place. See ISO 18923 and AES 22-1997.

DO NOT LIST

1. Do NOT touch tape surfaces with bare hands.
2. Do NOT put pressure on reel flanges.
3. Do NOT stack or place objects on top of unprotected tapes.
4. Do NOT force tapes into cases or machines.
5. Do NOT drop or throw tapes.
6. Do NOT splice any portion of a video tape.
7. Do NOT place tapes on or near sources of magnetic fields.
8. Do NOT play or spool tapes that are dirty, contaminated, or wet.
9. Do NOT play or spool tapes on a dirty, misaligned, or malfunctioning machine.
10. Do NOT store tapes in a basement or other area subject to dampness or possible pipe leaks.
11. Do NOT expose tapes to food or beverages.
12. Do NOT expose tapes to temperature extremes.
13. Do NOT expose tapes to water or high humidity.
14. Do NOT expose tapes to UV light, including the sun, for extended periods.
15. Do NOT attempt to clean tapes contaminated with adhesives, fungus, or unknown substances unless you have the necessary experience or training.