by Rich Rarey
((PUBLIC DOMAIN column for October 1995 Radio World...reprinted by permission of Radio World Magazine))
Display the recipe to 'cure' shedding tapes
|
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. |
|
| 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. |
In Part 2 We'll cover additional restoration information and give you a recipe for eliminating mold from your tapes.
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