A Recipe for Tape Restoration
copyright 1998 by Eddie Ciletti and updated 2011
The aging of magnetic tape concerns everyone. Even as you read this, a DAT tape is waiting to clog the heads of your most difficult-to-clean-machine. Unlike my usual visits to the digital domain, this is a detour into the magnetic past! Are you ready to explore the time-space continuum? TIME TRAVELING… PLEASE WAIT!
People who make analog recording part of their daily routine take for granted that the tape is new and the machine is operable. When called upon to re-master or remix a vintage analog recording, it goes without saying that the machine must be in top form AND that your business should be insured. That said, there is one variable for which you have no control: tape condition. This is especially true for mid-seventies era high-output tapes such as AMPEX 406/407 and 456, 3M 250, and AGFA 468. It does not exclude those made well into the eighties.
Don’t attempt to play a "vintage" tape before reading this article! In order to expect full recovery, tapes that have been shelved for an extended period deserve special treatment just like a scuba diver must slowly return to the surface.
All tape consists of three primary components: iron oxide, the "binder" or glue and a plastic carrier. Acetate — which does not stretch and can be brittle — was used until the sixties. Though its oxide color is typically reddish-brown, black oxides were also used. Mylar/Polyester eventually replaced Acetate. It handles stress well and never becomes brittle. Sixties-era Mylar tapes with black oxide will be the least problematic.
Figure One shows how easy it is to identify Acetate simply by holding it up to light.
(Acetate is translucent and Polyester is opaque.)
Tapes that have been poorly stored like the photo "uneven wind" will require extra care.
UNGLUEDOver time, the glue that binds the oxide to the plastic will absorb moisture and "break down." The symptoms of "binder breakdown" are immediately obvious even when rewinding. Tearing sounds and sluggish behavior are clues to quit before the oxide comes off. Machines with stationary lifters (Ampex 440/1200, MCI and 3M) will, in many cases, stall well before reaching the halfway point. An older Studer, with its rotating guides, may not reveal any warning signs until the tape is played.
Playing a bad tape is not recommended. Just trying to get through a three-minute pop song will require several cleanings. Once the precious sonic material collects on transport parts it is worthless, not to mention difficult to remove. Do you really want to risk damage to the master for the sake of getting a transfer? There is hope, so be patient.
Figure Two: Snackmasterâ FD-50
SHAKE ‘n BAKE: Part ISeveral years ago it was discovered that baking tape at low temperature reactivated the binder making tapes playable as new. While convection ovens and hair dryers have been called into service, the most elegant and affordable solution came from my brother-in-law Gary, a metallurgist in St. Paul, Minnesota.
STORAGE and HANDLING TIPSStoring tapes "tail-out" after having been played minimizes the effects of "print-through" and improves the chances of long-term survival. "Print-through" is a form of mechanically induced tape echo. The winning combination of high record levels and fast winding will transfer signals from one layer of tape to another. Tail-out storage will hide print-through as "post echo."
If you discover that the tape is unplayable while in fast wind, come to a slow stop. Fast winding the tape may cause further damage because oxide may adhere to the back of the previous layer. In addition, old splices may come apart. For the safest journey to the head, play the tape backwards first, then forward to create an even pack.
The best machines for winding traumatized tapes are those with ALL rotating guides. The AMPEX ATR-100 and most Studer machines are well suited to the task. In addition, you will want to remove the head assembly otherwise a gooey oxide/binder cocktail will quickly collect on all stationary surfaces (heads, lifters and guides). Model 800 series Studer machines are dangerously powerful so don’t use the remote, pay close attention and be ready to stop at a moment’s notice.
If uncertain of the tape’s condition but the pack is good, bake it anyway. Do not bake Acetate!!!
When baked, the tape will expand and become loose around the hub. For this reason, use flanges to protect the tape from coming apart. Cooking temperature is between 130°F and 140°F. Tapes wound on plastic reels with small hubs should be rewound onto large reels with NAB hubs. Be careful to thread the tape around the hub without any "folds." The goal is to minimize "mechanical distortions" that can be impressed upon subsequent layers causing dropouts. The "wind" must be smooth as if played!!!
I have received several e-mails regarding "cooking time" and temperature. Provided the wind is smooth, I am not afraid to bake a quarter inch tape at 135°F — for two hours — flipping every half-hour. You will find that cooking time varies with tape width, type, brand, condition and the number of reels being baked. Ampex tape from the seventies might require twice as much time as 3M tape from the eighties (as reported by Wendy Carlos when restoring her masters from that time period). Table One below can be used as a guide.
flip every 30 ~ 60 minutes.
If you are conservative about time and temperature and the tape still sheds after baking, put it back in! Being conservative for the sake of not losing high frequencies is a bit silly. Shedding during a transfer can be annoying at best and a pain-in-the-ass if you don't discover the flaw until way after the time of transfer. If you are concerned, consider baking a tone reel or test tape for evaluation purposes. Test tapes are not immune to shedding. Based on my experience, tapes can be baked more than once. Afterwards, return the tape to its box, allowing it cool for the same amount of time it was baked as a precautionary measure. Not all machines are equally gentle, a warm tape is more likely to stretch than one at "normal" temperature. To confirm the process, I sandwich a piece of cloth around the tape while rewinding. Figure Three shows what happens when the tape is not baked. A minimal amount of oxide shed is normal. Excess shed will cause friction to build up within the cloth. If so, re-bake.
Figure Three: An unbaked tape leaves a trail
POST RESTORATION STORAGEI recommend wrapping the tape in a plastic bag and including a Silica Gel pack to absorb moisture. Several surfers have dropped by to pass along these sources for helping to improve shelf life...
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