Baking Your Tapes is a Recipe for Success: Part 1

Bake the Flakes back into the Tape
by Rich Rarey
PUBLIC DOMAIN column for October 1995 Radio World Magazine.

"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-play 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 consumers 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

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 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.

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-inch reels at a time.
  3. LEAVE THE TAPE ON THE REEL. At these tepid temperatures, plastic reels won't be harmed.Tom Neuman says after baking, the tape will have a loose "pack" and if the tape is not on 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 re-baked 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 play-wound 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
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

In Part 2 We'll cover additional restoration information and give you a recipe for eliminating mold from your tapes.