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Author Topic: "Baking" old open-reel tapes  (Read 6186 times)

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Offline lsd2525

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Re: "Baking" old open-reel tapes
« Reply #15 on: December 10, 2020, 03:20:40 PM »
I might try an 8-track in the 'ol air fryer.

Seriously, this is a very interesting thread.
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Offline GLouie

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Re: "Baking" old open-reel tapes
« Reply #16 on: December 10, 2020, 03:34:56 PM »
I've never had a problem with plastic reels warping if the temperature is steady at 135F or so. Higher temps can cause a problem.
8 hours may be enough. I think it depends on the chemistry and storage of each tape. Many people tell me to do 24 hours - so I start at 10-12. I have no verifiable evidence that the longer time causes any damage, physical or magnetic, so longer may be safer as opposed to playing a tape that might have a severe case, and be underbaked. It is hard to determine how bad a tape is; I suppose you could try playing it and see how much scrapes off, if you dare.

I don't flip tapes, but I am lazy and it seems OK. Maybe if I did tapes wider than 1/4".


GLouie, the Nagra IV-S has no fixed guides in the path when a tape is being rewound, and the QGB large-reel adapter (which also has only rollers) gives further control over the tape tension.

But since my Nagra gear is in storage, for my first experiment I used a Revox A 77 with the tape going directly from one 7" reel to another, not passing through any guides or over any heads (which is beginning to sound like "over the river and through the woods"). If you hold down the play button, about 2/3 of the reel will shuttle from the feed side to the take-up side at a stately pace. The last 1/3 I drew across by turning the take-up reel manually. The tape pack is decently even--not perfect, but better than you'd get from a fast wind.

The cookie is in the oven now, set for 8 hours. Do you think with a 1/4" tape on a plastic reel, there's any point in flipping it at the 4-hour mark?

Offline DSatz

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Re: "Baking" old open-reel tapes
« Reply #17 on: December 11, 2020, 02:34:06 PM »
OK, here are my mixed results after 9 hours of baking at 135 degrees F, then letting it cool down for about a day before I got around to trying to play it.

The basic condition of the tape is greatly improved for much of its length. When spooling it between reels, I gently pinched a Kleenex tissue around the tape and only very, very little material came off, unlike before. But the tape was already so badly damaged before I baked it that most likely no part of it can be used any more. For much of its length it looks as though the tape is in the recorder backwards, with the oxide facing outward instead of inward toward the heads.

That's a shame; it was an audition tape that I remember making for a very good young conductor, who later went on to become rather well known.

The results were somewhat uneven, though. There are parts of the tape where the oxide layer still comes off in strips while winding it (see attached photos; in the one showing the Revox, what looks like tape wound partly over the left-hand reel is actually the oxide layer alone, which came off in lengthy strips while I was spooling the tape between reels--not winding it all that fast, either). So maybe Ampex is right, and 16 hours is better.

The clear plastic reel didn't warp at all that I could see.

--best regards

Edited later to add: This begins to make a kind of cruel sense to me. The oxide layer contains the binder that holds it to the backing. Once that binder becomes ineffective due to decomposition, the oxide layer has no preference for whether the "back" of it will remain with the layer of backing that it was originally attached to, vs. its "front" adhering to the "back" of the backing layer that it's pressed up against on the reel. It's a 50/50 proposition.

So as GLouie said (maybe in text that was added later? I don't remember seeing it before), it's better to have loved and lost--I mean, it's better to bake too long rather than not long enough--and in my opinion one shouldn't try to do ANYTHING with the tape before baking it. I'm not sure that I would advocate spooling it, no matter how gently and slowly, to improve the wind prior to baking; I think that I was wrong to do that in this instance.
« Last Edit: December 11, 2020, 02:58:20 PM by DSatz »
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Offline audBall

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Re: "Baking" old open-reel tapes
« Reply #18 on: December 11, 2020, 03:06:10 PM »
I wonder if the smooth winding (library wind) suggestion is intended to allow for a more uniform spacing/wind of the tape reel such that the later (convection) baking process would permeate/distribute the heat more uniformly (less "unevenly") throughout and around the tape.

Although I'm not sure how one would accomplish that if the reel needs to be baked just to be used.

/limited use comment

Offline Gutbucket

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Re: "Baking" old open-reel tapes
« Reply #19 on: December 11, 2020, 04:43:24 PM »
Happy to see this thread, and my condolences on the end result of that particular first test.  This gets me thinking again of some cassettes I should transfer, 'though I'm sure that will soon pass and I'll be able to put this out of mind again.  Anyone have experience baking cassettes?  Wondering if the the cases need be disassembled and spools removed, since plastic cassette housings are considerably thinner than most 1/4" tape plastic reels.  These are 80's era, stored for the past 25+ years, and I suspect would benefit from baking.  Some 4-track, some 2-channel masters.



« Last Edit: December 11, 2020, 04:49:04 PM by Gutbucket »
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Offline EmRR

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Re: "Baking" old open-reel tapes
« Reply #20 on: December 11, 2020, 11:13:01 PM »
Happy to see this thread, and my condolences on the end result of that particular first test.  This gets me thinking again of some cassettes I should transfer, 'though I'm sure that will soon pass and I'll be able to put this out of mind again.  Anyone have experience baking cassettes?  Wondering if the the cases need be disassembled and spools removed, since plastic cassette housings are considerably thinner than most 1/4" tape plastic reels.  These are 80's era, stored for the past 25+ years, and I suspect would benefit from baking.  Some 4-track, some 2-channel masters.

Word is cassettes don't need baking.  I've never heard of a gooey one.  Warped shells, leader splices gone bad, yes. 
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Offline justink

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Re: "Baking" old open-reel tapes
« Reply #21 on: December 11, 2020, 11:18:44 PM »
I wonder if the smooth winding (library wind) suggestion is intended to allow for a more uniform spacing/wind of the tape reel such that the later (convection) baking process would permeate/distribute the heat more uniformly (less "unevenly") throughout and around the tape.

Although I'm not sure how one would accomplish that if the reel needs to be baked just to be used.

/limited use comment

This is what I was going to comment.  If you can loosen the wind, it would be more surface area/better.  But if the tape is stuck together, attempting that would ruin.  so...  :shrug:

I wonder if a 5* F lower temp for longer might be better than attempting a library wind?  I've never attempted this but definitely interested in the process.  I deal with a lot of heat transfer at work in a commercial sense.  I don't see a longer bake time being detrimental if the heat isn't too much and there's plenty of convection/flow.  We are talking about metals and plastics, not food.
« Last Edit: December 11, 2020, 11:20:52 PM by justink »
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Offline jerryfreak

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Re: "Baking" old open-reel tapes
« Reply #22 on: December 12, 2020, 12:01:58 AM »
I mean, it's better to bake too long rather than not long enough

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Offline DSatz

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Re: "Baking" old open-reel tapes
« Reply #23 on: December 12, 2020, 01:55:38 AM »
Actually I have one cassette (out of many hundreds that I've recently transferred) which I may want to try baking. The tape plays OK for a minute or two, but then begins to wander out of the path and pull out of the cassette on the supply side, while getting stuck on the take-up side (i.e. it "throws a loop" at 1-7/8 ips and I have to stop the tape).

I've exchanged the cassette housing twice already but that hasn't helped; I think it's the tape stock itself which is the problem. It's an Ampex-brand cassette, FWIW.

I'm sure I've read about other people who baked cassette tapes--just not nearly as often as I've read about open-reel tapes being treated. When I get to it, I'll let y'all here know whether it helps or not. I might well take the tape out of the cassette housing to bake it, just to eliminate one "unknown".
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Offline jerryfreak

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Re: "Baking" old open-reel tapes
« Reply #24 on: December 12, 2020, 02:06:22 AM »
it seems the bad tape was era-specific?

i first heard of "baking" in 1990 when healy, et al were talking about it for mid-70s reels

as i type this, the common 80s cassettes are relatively twice as old as that, but perhaps they figured it out and were able to improve by then?
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Re: "Baking" old open-reel tapes
« Reply #25 on: December 12, 2020, 09:44:18 AM »
it seems the bad tape was era-specific?

I was told that certain formulations were more prone than others to deterioration.
« Last Edit: December 12, 2020, 10:07:44 AM by anodyne33 »
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Offline GLouie

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Re: "Baking" old open-reel tapes
« Reply #26 on: December 12, 2020, 03:25:20 PM »
OK, here are my mixed results after 9 hours of baking at 135 degrees F, then letting it cool down for about a day before I got around to trying to play it......

Very sorry. I never personally spool before baking, and out of many hundreds, maybe thousands of baked Ampex 1/4 reels, exactly one had the oxide separate cleanly like that after baking. My guess is that you'd have had the same problem after baking.

Sticky shed is usually known on tapes that have backcoat, and apparently manufacturers started using urethane in the binder for the backcoat and the oxide layers. My feeling is that even among certain manufacturers and tape "models" that there is a wide variation in decomposition. I am guessing there is batch inconsistency as well as storage differences. In the USA, Ampex is most cited, but also 3M, Agfa, etc. Other tapes may have other problems that may make them seem sticky, and baking is not recommended.

There is one fellow who says to "simply" remove the back coat, which he says is the root cause of the problem. A few test demonstrations have apparently been successful, but he has yet to show a practical method of doing this.

Here are some references. I would probably start with the Richard Hess paper.


---Sticky Shed References from the 1980s-90s---

IASA Phonographic Bulletin #61, "Restoration of Tapes with a Polyester Urethane Binder" 1992

Studio Sound, May 1991 - Barry Fox's Business column, Sticky Shed Update

Studio Sound, December 1990 - Tape Life: An Era of Concern by Barry Fox

Audio, November 1990 - Archival Revival by Michael Stosich

Audio, July 1990 - Bert Whyte's Behind the Scenes column (I bake for Whales)

MIX, May 1990 - Philip De Lancie's Tape and Disc column "Sticky Shed Syndrome, tips on saving your damaged master tapes"

Recording Engineer/Producer, July 1988 - Studio Update:
Talkback: Binder Breakdown in Back-Coated Tapes by Scott Kent

JAES, April 1988 - Increasing the life of your Tape by Jim Wheeler, Ampex.

Broadcast Engineering, October 1987 - Preserving Magnetic Tape by Walter Davies (the LAST Factory)

IEEE Transactions on Magnetics, September 1985 - Kinetics of the Humid Aging of Magnetic Recording Tape, by H. Neal Bertram, Ampex.


---Other references---

The Ampex Patent
U.S. Patent 5,236,790


Richard Hess
Tape Degradation Factors and Challenges in Predicting Tape Life
ARSC Journal, volume 39, No. 2 (Fall 2008) page 240
http://www.richardhess.com/tape/history/HESS_Tape_Degradation_ARSC_Journal_39-2.pdf

Hess' personal site with tape degradation info for several tapes
https://richardhess.com/notes/formats/magnetic-media/magnetic-tapes/analog-audio/degrading-tapes/


Sonicraft (New Jersey) on tape baking
https://www.sonicraft.com/tape-baking/


Eddie Cilletti
If I Knew You Were Coming, I'd Have Baked a Tape!
http://www.tangible-technology.com/tape/baking1.html


Mike Rivers
Early article with caveats
https://mikeriversaudio.files.wordpress.com/2020/07/how-to-bake-a-tape_original_1990-article.pdf


ARSC (Association for Recorded Sound Collections)
Guide to Audio Preservation (CLIR pub 164)
https://www.clir.org/pubs/reports/pub164/


British Library
Manual of Analogue Sound Restoration Techniques
https://www.bl.uk/help/manual-of-analogue-audio-restoration-techniques


IASA (International Association of Sound and Audiovisual Archives)
TC03 (general planning), TC04 (restoration guides)
https://www.iasa-web.org/tc04/audio-preservation
Web version free to public; PDF free to IASA members; paperback for a fee.




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Re: "Baking" old open-reel tapes
« Reply #27 on: December 12, 2020, 08:36:17 PM »
Ah sticky shed. 

I've finished a project for a radio station on old reel to reels, literally about a 200 reels.  We baked them all in a food dehydrator at the lowest setting, for about 4 hours minimum, overnight was the longest.  Transcribe the tapes immediately.  Well, wait until they cool, then transcribe them.

Perhaps it goes without saying but gently fast forward and reverse the tapes to loosen them up before transcription.  Of course, clean and demagnetize your heads. 
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Offline DSatz

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Re: "Baking" old open-reel tapes
« Reply #28 on: December 13, 2020, 09:45:26 PM »
I put the tape back into the dehydrator for 16 further hours of baking, let it chill out for a day and a half, then transferred one movement of the Beethoven Seventh Symphony using the Nagra that the tape had been dubbed on ~40 years ago. The attached photos show the disastrous result.

Please keep in mind that this tape wasn't wholly typical, because it had already been damaged badly by trying to rewind it; the oxide/binder layer in many places came off the backing layer that it belonged on, and either flew off in random directions or stuck instead to the back of the backing on the adjacent layer of tape on the reel. Note one peculiar thing that occurred sometimes during playback: An oxide/binder layer and a backing layer fed through the tape path at the same time, but separately (see the two arrows that I added to the second photo below). My apologies for shadowing my own photographs, but the only light source was overhead.

What I'm not seeing--and what gives me hope for later work with tapes that haven't been "pre-ruined" before baking--is any of the sticky stuff on the heads, guides or rollers that came off in large amounts the first time I tried to play any of this tape. All this loose oxide/binder stuff very well might have separated from its backing before I baked the tape. (At least I hope that's true.)

(And now if I want to send holiday greeting cards to my engineer friends, I have the photos!)

edited later to add: What also gives me hope: As I've transferred this tape piece by piece, I've stopped to clean up between pieces--then I've rewound the tape slightly so as to get the correct transitions between the pieces. Whatever material had come off the backing while playing each piece, when I rewound to the end of the previous piece and then played again from there, no further material came off until I got to the part I hadn't played before.
« Last Edit: December 13, 2020, 11:29:20 PM by DSatz »
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Offline EmRR

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Re: "Baking" old open-reel tapes
« Reply #29 on: December 14, 2020, 12:04:56 AM »
Holy crap that is a nightmare to look at!
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