Baking Old Tapes is a Recipe for Success

by Rich Rarey

(This article began as a PUBLIC DOMAIN column for October 1995 Radio World...reprinted by permission of Radio World Magazine)

Part I

"The important thing to remember is: Don't Panic. Your valuable tapes can be returned to playable condition after careful baking."

Recently, a record producer called in a fit of mild panic. He said he had a dozen two-inch reels of multitrack tape, priceless in content, and unplayable in their present form.

I inquired as to the noise the reels made as he attempted to play them. "SQUEEEEEEEEEEK!", he said. Did his tape leave dusty, rusty particles on the guides and heads? He said yes. No doubt then remained. His tapes had the dreaded Sticky Shedding Syndrome. I reminded him that before he start a national telethon to raise money for research, a cure had already been found. When he realized that his precious master tapes were in no immediate danger, and could temporarily be restored to usefulness, he calmed down and rang off. The producer's call piqued my interest. What would you do if your ancient, valuable tapes started sticking and shedding? What are the manufacturer's current recommendations?

Remember: Don't Panic!

William Lund, Senior Technical Service Engineer at 3M's Maplewood,MN headquarters said the first and foremost thing is "DON'T PANIC". In fact, it's so foremost that he repeated: "DO...NOT...PANIC!" According to Lund, the only 3M brand of tape stock affected is 226,227, and to a lesser extent 806 and 807, manufactured from 1978 through the early 1980's.

Tom Neuman Senior Staff Engineer in charge of the Recording Technology Group at Ampex Corporation's Redwood City's headquarters had a similar response to those asking about tape shedding: "DON'T PANIC!" Neuman says that various Ampex tape stock from the early 1970's to early/mid 1980's has been found with the syndrome from Two inch Quad video tape,to half-inch EIAJ video tape (the industrial/educational Sony "Rover" format) and the ubiquitous Ampex 406 1/4inch analog mastering tape. Because the 406 stock was a big seller, with about one million reels leaving the Ampex factory every year, this is the stock that affected the most users.

How did these tapes become damaged?

To understand how these tapes wound up with Sticky Shedding Syndrome, it's important to view the manufacturing process from a historical perspective. Originally, the magnetic oxide was deposited on a paper backing. Paper had serious drawbacks. Moisture could cause the backing to grow and shrink. As the noise level of recording tape is dependent on the smoothness of its oxide surface, paper's microscopically rough surface made it impossible to make a smooth oxide layer over a such a rough backing. Acetate, according to Bill Lund, made a smoother backing material, but it was water based. DuPont's Mylar (polyester) made an excellent backing material, tough, smooth and stable.

Attaching an oxide coating to polyester is harder than just painting it on; the raw oxide has to be ground to a fine evenness, without clumps or odd size particles, as the nature of high quality magnetic recording dictates that the particles must be regular and small. The oxide is mixed in vats with a binding agent that Lund describes as an "exotic, organic soup". The binder is a complex polymer chain of organic chemicals and lubricants that will cause the oxide to attach permanently (we hope) to the backing, and yet permit the easy sliding of tape-across-head. The binder's chemical recipe is unique to each manufacturer, and closely held information. Interestingly, it appears every tape manufacturer has had a sample of its competitor's products rigorously analyzed for its composition, so the tape users are really the only ones who don't know (or care) what makes up the binding agent. Volatile chemicals are added to the production vats that act as "carriers" to permit the binder and oxide slurry, now properly known as a 'dispersion', to be sprayed ("coated") onto the plastic backing. The resultant raw product is then heated to eliminate the volatile carrier. The resultant vapors are captured and recycled.

Why aren't all tapes affected?

How is it, then, that certain tape stocks became sticky and shedding? According to Tom Neuman, no two chemists agree as to WHY it's happening, but the effect is this: the binder's long, complex polymer chain breaks down into smaller polymer chains that might be likened to a set of microscopic sticky tinker toys. It these unbonded parts of the chain that appear to cause the stickiness. It's believed that the particular combination of a certain oxide with a particular binder will, over time, cause the binder to break down.

Moisture in one's archive storage area will exacerbate the breakdown. Neuman says the analytical tools of the 1970's weren't sharp enough to reveal the binder limitations at the onset. Tape deterioration was recognized in the early 1980's when a major remastering phase for the emerging Compact Disc technology occurred. Users found their irreplaceable tapes sticky and unplayable.

The answer's in the "mix"

Ampex chemists then started analyzing the problem as the frustrated users tried their own home-brew solutions, from talcum power (don't even consider this--it'll rip the oxide off the backing and ruin your heads) to alcohol washes (this will merely swab the oxide off the backing, and ruin your tape).

The chemists discovered the only cure was...to recure the tape through careful heating. During heating, the binder's stubby chains rebonded into the proper longer chain, and made the tape almost as good as new.

How to use the recipe

Here's the recipe for restoring your tapes, as patented by Ampex (don't worry, anyone can use it!). First, get a reliable, even heat source that can maintain 50 degrees Centigrade (about 121 degrees F.) plus or minus a few degrees. Many people use a convection oven to restore their tapes. It's just an oven with an internal fan to ensure even heating. Bill Lund reports that some are using a food dehydrator oven that makes an inexpensive heat source. Tom Neuman says that one record company constructed their oven from a cardboard box, a hair dryer and a candy thermometer!

Ampex uses a BLUE M industrial laboratory oven for their research, this unit costing in the hundreds of dollars. The key is: RELIABLE HEAT TEMPERATURE. A candy thermometer in the oven will help you monitor the desired temperature. Neuman says that regular cooking ovens should be avoided; their thermostats may not have high enough "resolution" to deliver consistent heat at these "low" temperatures.

  1. DO NOT PREHEAT! Put your tapes in when the oven is cold. Tape does not like temperature shock any more than humans.
  2. DO NOT FILL THE OVEN MORE THAN 50% FULL. It will make even heat distribution difficult. An oven with a two cubic foot interior can bake about eight 10" reels at a time.
  3. LEAVE THE TAPE ON THE REEL. At these tepid temperatures (see temperatures above), plastic reels won't be harmed.Tom Neuman says after baking, the tape will have a loose "pack" and if the tape is noton a reel, annoying tape spillage can occur.
  4. BAKE FOR HOURS AND HOURS. Bill Lund at 3M recommends baking eight to ten hours and allow the reel to cool down slowly. Tom Neuman at Ampex recommends baking for 24 to 48 hours with the same gradual cooling-down period. Severely shedding tape can be repeatedly baked until it's playable. Does the difference in hours matter? Probably not. The tepid temperatures won't damage the plastic tape or reels, or demagnetize the tape. Both Lund and Neuman report complete success with baking any tape that has Sticky Shed Syndrome. How long will the binder remain intact? Apparently tape will remain playable for a period of weeks to months, depending on the severity of the shedding. When the tape begins to exhibit signs of shedding, they can be rebaked again and again without damage.
  5. ALLOW THE REELS TO COOL SLOWLY. You can allow them to cool within the oven when the baking cycle is finished. The tape will naturally have a loose pack on the reel, and should carefully be playwound for proper pack and stored tails out.
  6. DO NOT THROW AWAY YOUR MASTER REELS. Both Neuman and Lund stress the fact you can rebake the reels as needed, so there's no reason to discard them.

The Problem is widespread

Tom Neuman says that he has seen tape from every manufacturer exhibiting Sticky Shedding Syndrome. Why? Every tape manufacturer has to turn to a small handful of companies for the raw materials that compose recording tape; petroleum companies for plastic materials and pigment companies (!) for the oxide. It's not the ingredients that make a recording tape unique, Neuman says, but rather the unique way the raw materials are processed into the complex material called recording tape.

Part II:Follow up, and, what about the mold?

Radio World Readers Respond...

We've received engaging E-Mail from several readers for our "Bake the Flakes Back into the Tape" column of several months ago. Greg Guarno asked us

  1. What are the audible effects of 'baking' the tapes? I have heard that it dramatically increases 'print through', and that it may erase some of the high frequencies.
  2. Are Ampex or 3M now using a different binder chemical, and if so, has it held up any better?

We have been dealing with this problem for many years,and it seems to me that I've encountered this sort of shedding on tapes that are only 4 or 5 years old. This would mean that they were manufactured AFTER the symptoms were already known, which suggests to me that they went on making the defective tape for at least some time. I should add that tapes that are VERY old, from the 50's and 60's, do NOT seem to exhibit this shedding.

"Baking tapes leaves no audible effects, and it won't affect lubricants, additives or plastic reels."

I posed these questions to our two tape experts: William Lund, senior technical service engineer at 3M, and to Tom Neuman, senior staff engineer in charge of the Recording Technology Group at Ampex. Both experts said baking tapes at the prescribed temperatures will have no apparent audible effects. Neuman says a temperature at 120 degrees F does not affect lubricants or other additives, it does not destroy splices, plastic reels or leader materials. He adds that after personally baking 2,000 tapes, he has not noticed any adverse effects. Lund says that high frequencies do reside nearest the actual surface of the tape, but unless that surface is disturbed in some way, the baking process does not change the magnetic properties of the oxide particles which make up the magnetic coating of the tape. In Tom Neuman 's opinion, the only risk during baking would come from stray magnetic fields inside the oven from the electric fan motors, heating elements or solenoid coils. He adds that it's a good idea to check for any such stray fields before baking a tape in an unknown oven.

What is print-thru? A definition

Print-though, according to our old Audio Cyclopedia, is the "unwanted transfer of a signal from one layer of tape to another by magnetic induction". According to Bill Lund the print-through phenomena is also not well understood and even more elusive to quantify. He says it is a characteristic of the oxide used and how it is prepared for use in the chemical binder of the tape. Interestingly, print-through reaches a "terminal value" after a period of time. That is, the tape will achieve the most print- through it can have, and the amount of print-through thereafter will not increase. The time it takes for a tape to reach this "terminal value" is dependent on the tape (and the oxide used on it) and the storage temperature. Lund says that since the oxide and the tape are pretty much fixed, the biggest variable is temperature. A tape stored at a very low temperature will take a considerable time to reach it's terminal value for print-through, whereas a tape stored at high temperatures will achieve it's terminal value much more quickly. The terminal value is the same in both cases, it just takes much longer to get there at low temperatures.
He advises not to worry about the 'baking' process and it's potential for causing harm to the valuable tapes, because it doesn't happen.

What's different now?

What are Ampex and 3M doing differently? Tom Neuman says that when the sticky shedding syndrome was first noted and the effect fully understood about nine years ago, ALL tape manufacturers began the process to improve the tape's archival stability. Bill Lund points out that "you do not build a new binder and chemistry overnight", but rather attempt to design new tape stocks with greater longevity. He points to 3M's 900 series of tapes as such an attempt, but cautions that even with all manufacturers using accelerated aging tests to predict the behavior of their product, the outcome is still...a prediction.

The binder problem did not appear until 7 or 8 years after introduction of the product, and since predictions didn't show the problem at all, Lund says it "hit us as a real surprise". One interesting aspect of a particular product's age, Tom Neuman points out, is that manufacturers don't have control over the age of tapes sold by some of the supply houses around the country. A reel purchased 5 years ago could actually be 8 or 10 years old. Neuman recommends buying tape stock from well known and reputable distributors, and avoiding garage and surplus sales, where, he says,"nobody has any idea of how the tape had been stored or the actual age of the tape."

Bring back the old tape formulation -- NOT!

Why then, with all the excitement over binders becoming unbound, don't the tape companies return to the old tried-and-true formulations that worked so well? 3M's Bill Lund says that in the quest for tapes with higher output, lower noise and lower print- though, different oxide technologies were required. The modern, better-performing oxide formulas are chemically incompatible with the older binders from 40 years ago. Consequently, if manufacturers were to return to those old binder compositions, we'd see a return of tape stocks that had inferior print-through, maximum output, and bias noise floors.

Moldy, Moldy, Moldy!

Another reader, Charlie Mayer at Swarthmore College, wrote asking what to do with archival tape that is growing yellow, green and white mold. Apparently this mold is not of the school colors. Ampex's Tom Neuman provided a ready recipe for restoration:

  1. Open all affected boxes and remove the reels.
  2. Place the opened boxes and tapes in a dry, warm room so that the tapes can thoroughly dry. This may take anywhere from a few days to a couple of weeks.DO NOT bake tapes that have mold growth, as this will just bake the mold into the tape, and permanently stain the surface of the tape!
  3. After the tapes are thoroughly dry remove the flanges, if the tapes are on metal reels, and thoroughly clean the mold off with a 3% solution of Hydrogen Peroxide. This can be purchased at any drug store. Hydrogen Peroxide will effectively clean off the mold and its antiseptic properties will help to inhibit future mold growth (It also comes in handy if you cut yourself while removing the flanges). It is especially important to thoroughly clean any stick-on labels that may be on the flanges as they seem to be great breeding grounds for mold.
  4. Next comes the awful part; load the reel of tape on a transport (after replacing the flanges) and slowly wind the tape forward by hand and inspect the surface for sign of mold. If any mold is seen it can be wiped off with the 3% Hydrogen peroxide solution and a TexWipe or similar lint-free cloth. Follow by wiping the excess liquid off with a dry wipe. Pay particular attention to the edges of the tape as this is where mold growth generally starts. The time this step will take varies greatly dependent on the severity of the mold growth and your patience.
    If the entire tape is affected you can use a slightly damp (with Hydrogen Peroxide) cloth held up against both sides of the tape and run the tape through at the slowest speed you have available. If you use this method, make sure that you repeat the process several times with a dry wipe to completely dry off the tape's surface before putting the tape back in storage.
    Hydrogen Peroxide is the only material we can recommend for cleaning the surface or backcoat of a tape. It does not damage any of the tape's chemical components and is safe to the user. DO NOT use alcohol or other types of cleaning solvents as they may permanently damage the tape! In many cases the surface of the tape may be stained from the mold even after cleaning. This has not proved to be a functional problem, just a cosmetic one.
  5. Finally, thoroughly clean the storage box with Hydrogen Peroxide and dry thoroughly. Quite often the box is thoroughly damaged, and a new box may be needed. In the case of historical material the original box may need to be cleaned and stored separately from the tape. Mold growth usually initiates from moisture trapped in the box material or inside the box.
  6. Before putting your tapes back into long-term storage make sure there is no trapped-in moisture inside the box. It is not a good idea to put tapes away when the humidity and temperature are high, as this is the air that will be trapped inside the box for the next 20 years.

Neuman says he has personally cleaned dozens of tapes using this method and it seems to work quite well.

We wish clean, dry, securely bindered tape to you all.

Author's note: Since these articles were published in 1995, the tape industry has changed dramatically; 3M no longer manufactures recording media, and the division of Ampex that made recording tape has been spun off, and is now known as Quantegy. Bill Lund is working with 3M in their commercial graphics division. You can reach him by emailing: wflund at mmm.com, or by emailing: 75763.2162 at compuserve.com.
Tom Neuman has left Ampex and is persuing interactive media development. You can reach him at Contact by emailing: Wildware at aol.com
Interestingly, Bill Lund says Quantegy has recently purchased 3M's recording media intellectual property rights and remaining tape stock.

Rich Rarey a Technical Director for National Public Radio, and can be reached by emailing: rrarey at npr.org

Please do not reprint without permission of the author.