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  Tape Baking and Restoration  
 

THE SONICRAFT GUIDE TO TAPE BAKING, RESTORATION AND PRESERVATION

-- by Steve Puntolillo, Sonicraft A2DX Lab

If you are here, you are probably most curious about "tape baking", also called "tape incubation" and "heat treatment". One thing is certain: no one bakes a tape unless they plan to play it. So, I'll go beyond the subject of tape baking into general tape restoration and preservation. But first, I'll give you the answers you came here for:

Why would anyone bake tapes?

There has been a chronic problem with certain formulations of audio tape manufactured from the early- '70s to the present that render them difficult or impossible to play safely. The ad hoc term for the problem is "Sticky Shed Syndrome" or "SSS". For those specific types which will successfully respond, the most practical and efficient way to reclaim tapes with Sticky Shed Syndrome is to incubate (or "bake") them.

In the majority of cases, when tape baking is executed properly, the tape will again become temporarily playable with no perceptible deterioration of the sound of the recording.Incubator

Many tape restoration facilities use kitchen appliances for baking tapes. For the ultimate in safe handling, we use a Fisher Scientific incubator designed for critical use in research labs. A precision piece of laboratory gear, it can hold temperature to within 1/10 of a degree Celsius. Drift of temperature beyond 3 degrees will shut the unit down.

Spacious interior dimensions allow the full range of tape reel sizes up to 16" reels of 2" tape.

When you send or bring your tapes to us for transfer, we do whatever it takes to make them safe to play and capable of rendering the best transfer possible.

Why can't I play tapes with SSS?

In severe cases of SSS, adjacent layers of tape bond to each other making it impossible to wind, rewind or play the tape without damaging it. These tapes stick to themselves and to anything in the tape machine that they pass over. They sometimes "shed" -- some of the layer of the tape that holds the signal (sound) gets left behind on surfaces the tape passes over or simply dislodges and falls away. SSS tapes often squeal and their stickiness can cause speed (pitch) fluctuations ranging from subtle to drastic to finally bringing the entire playback machine to a stop.

To make matters worse, tapes suffering from Sticky Shed Syndrome were made with base materials that tend to stretch rather than breaking cleanly. If you can imagine the combination of sticky surface and stretchy backing, you will understand how easy it is to irreparably damage the tape just by attempting to rewind or play it.

How does tape baking affect tapes with SSS?

In the cases where tape baking is successful, it temporarily re-stabilizes the tape allowing it to be played. Under the right circumstances, tape baking works and we routinely get tapes to play like new. But, before you rush off to throw your irreplaceable masters into the oven, please understand three things: to be successful in tape baking and not damage the tapes (1) you must be properly equipped, (2) you must have a knowledge of which tape formulations you can bake and which will be damaged by baking, and (3) experience counts -- tapes have continued to age and we have found successful tape baking is rarely achieved with the simple "recipe" originally published decades ago.

Here at Sonicraft A2DX Lab, we know tape baking. We've successfully baked countless tapes. We know which tapes will respond to baking and how to adjust the process on a tape-by-tape basis. We also know which formulations can be damaged by baking. We have established procedures and proper equipment for evaluating the condition without damaging the tape in the process and we have invested in the first-class laboratory-grade equipment necessary to keep your tapes safe and do the job right.

I heard that the problem was moisture absorbed into the tapes. What if I've taken really good care of my masters and kept them in a cool dry place?

It's wonderful that you've done that. But, Sticky Shed Syndrome is more complex than just moisture absorption. It's a result of a flaw in the formulation of the tapes coupled with the effects of time. Good storage conditions will not prevent it. However, by storing your tapes properly, you have certainly helped to reduce the severity of the condition and extend the overall life of your masters.

So, then, how did my tape get sticky?

The primary ingredient in the surface coating of magnetic tape is one of many types of metal oxide, which is literally rusted metal ground into dust. This coating of microscopic metal particles is suspended in a thin chemical compound (the "binder") that adheres them to the tape backing. Magnetic tape recording works by putting a magnetic charge (alternating plus and minus following the shape of the sound wave) into the oxide during recording. On playback, the changing magnetic charge on the moving tape reproduces the image of what was originally recorded. The more accurately the charge on the tape captures the shape of the original waveform, the more accurate the recording will be.

Over time, the properties of the tape chemistry change. Sometimes, the coating on the back of the tape (backcoating) and the coating on the front of the tape (oxide and binder) begin to merge into each other. The problem is not uniform but varies from manufacturer to manufacturer, formulation to formulation, year to year, batch to batch, reel to reel and sometimes even within a single reel.

There are several different symptoms attributed to SSS. Tape binder includes lubricant which may retreat from the surface, the binder can absorb moisture from the environment making it sticky, and the basic operating temperature requirement of the tape can fall so that the tape is no able to run smoothly at room temperature.

If you really want the story in full technical splendor, there is a magnificent paper written by Richard Hess that can be obtained from the Audio Engineering Society (http://www.aes.org) either as part of the 121st convention preprints or individually. It's titled: "Tape Degradation Factors and Predicting Tape Life".

What happens if my tapes have SSS and I try to transfer them without tape baking?

You will not get a good transfer for several reasons. Tape oxide residue will quickly build up on the playback head. Just the slightest loss of tape to head contact -- even a microscopic amount -- immediately degrades high frequency response, audibly clouding the sound. SSS is usually accompanied by tape squealing which will be picked up and recorded in your transfer. And with the drag of sticky tape on fixed surfaces, tape speed will waver resulting in wavering pitch. In severe cases, you will outright damage your tapes.

You might also damage the tape machine itself. The challenged tape resists being pulled across heads, guides and tape lifters, overtaxing the reeling motors and their drive circuitry, perhaps to the point of failure. Finally, there have been rare instances where major damage was done to expensive tape machine heads. In one case documented by JRF Magnetic Sciences, 40% of the machine's head life was eaten away in a single transfer session.

Does incubating or "baking" the tapes damage them?

Apparently not. On the other hand, trying to transfer tapes with Sticky Shed Syndrome without correcting the problem first could very easily damage them. There's some conversation that eventually repeated baking could have detrimental effects on your tapes. Although we have not seen supporting evidence that this is true, I would advise that you try to limit the amount of times you have your tapes baked.

What else do I need to know about the tape baking process?

Tapes properly treated for Sticky Shed Syndrome will play long enough for us to transfer them for you. Eventually, the condition will return. This could happen in days, weeks, months or years. There is currently no way to estimate the amount of time it will take a given tape to relapse. If you ever need to transfer the tapes again, the process can be repeated if necessary. So, hang onto your tapes and keep them properly stored in case you ever need them again.

There's more guidance on how to best store your tapes below.

So, you've baked the tapes and we're home free, right?

I hope so. Generally, the answer is "yes", but SSS is not the only problem we might have to deal with. Sometimes bad things happen to good tapes. Depending on storage, handling and the effects of time, audio tape can deteriorate or be damaged in the following other ways:

Non-SSS Shedding

Separation of the binder from itself or the base material is called "shedding". A mild case of shedding is seen as a small loss of oxide or backcoating on each pass of the tape through the tape path. Even brand new tapes sometimes shed slightly.

As we discussed, SSS tapes often shed, but SSS is not the only possible cause. Non-SSS shedding can be caused by a number of factors, but is usually caused by decomposition due to age, heat, extreme dryness of atmosphere, or manufacturing defects. In progressive stages, the oxide coating flakes off of the tape backing in chunks resulting in complete "dropouts" of the signal - a permanent loss.

Obviously, tapes that are shedding must be handled with extreme caution and not played or handled any more than absolutely necessary. Sometimes we may be able to "re-hydrate" a tape that is shedding and make it playable -- at least long enough to rescue what's on it.

It should go without saying that a tape that is shedding from dehydration should NOT be baked.

Decomposition of splices

Performances recorded on magnetic tape often contain splices, and it is very common to find that the splicing tape has decomposed. Ironically, tape baking that makes the tape playable may sometimes accelerate the failure of splices.

Three types of splicing problems come to mind. The first type of problem with decomposed splices occurs when, over time, they ooze adhesive and cause adjacent layers of tape to be stuck together. When this happens, there can be some loss of oxide or backcoating around the area of the splice and the adjacent layers of tape. The tape or oxide coating could be damaged further if winding or playback is attempted before separating the affected layers - a painstaking procedure.

The opposite problem occurs when the splicing tape adhesive dries up and fails. In these cases, the splices "let go" and must be replaced.

Even more insidious is the splice that has stretched leaving an exposed adhesive area that can come in contact with the components of the tape path. Unwitting attempts to play, rewind or fast forward the tape can cause the splice to fail or stick to some component of the tape path resulting in tape being snapped, stretched or wound into the machine’s spinning capstan.

You can easily see why we use no remote controls on our tape machines. Our engineers stay right at the machine whenever tape is moving.

Physical damage or contamination

There can be more to restoration than baking. Various types of contaminants can find their way into a tape: dust, nicotine, mold, etc. In fact, the tape itself can sometimes "manufacture" its own contaminants.

Even the most microscopic particle or coating can substantially reduce and destabilize high frequency response. If some of these contaminants leave the tape and adhere to the playback head, they can build up and make the problem even worse. We've experienced tapes so badly behaved that we can actually hear playback get progressively muffled as the tape plays. Part of our evaluation of tapes is to check them for cleanliness and if found to be challenged in this respect, we will clean them.

To take tape cleaning to the ultimate, we consulted with a designer of tape cleaning systems and used proven tape cleaning technology to develop our own highly sophisticated cleaning machines, tailored specifically for safe and effective cleaning of our client's audio tape recordings.

Custom tape cleaning machines
Sonicraft A2DX Lab's custom tape cleaning machines

Based on Studer tape transports, these machines feature: (1) Vacuum removal of loose contaminants as the tape comes off of the reel, (2) optional sapphire cleaning blade, (3) Motorized Pellon cleaning station, (4) Backcoat cleaning station, (5) Vacuum removal of contaminants during rewind.

Tape cleaning machine
Components of Sonicraft A2DX Lab's Tape Cleaning Machines

How well does does all of this work? You might be surprised. For example:

Before   After
Before tape Restoration
  Tape After Restoration
2" 16-track Master Before Restoration   2" 16-track Master After Restoration
This is a 2" 16-track master from the mid-1970s which had been in a flood and then stored for several years under the worst of conditions. The box was literally disintegrating, the metal hub retainer from the box was fused to the interior of the tape hub and corrosion in the hub was so bad that the tape could not be mounted on any of our machines. The condition of the tape itself was so deteriorated it could not be wound or played.   This is the same 2" 16-track master after A2DX restoration. During the restoration process, we baked it, cleaned it, remounted it on a new hub, leadered and re-boxed it. It transferred with perfect results. Here you see it after transfer, library wound and ready to be placed in safe storage.

Tape Storage Guidelines

In the best of circumstances, your tapes should be in a secure storage area that is designed for media storage and appropriately climate-controlled for both temperature and humidity. If this is not practical, here are some do-it-yourself guidelines:

(1) Store tapes at a temperature between 50-68 degrees Fahrenheit with humidity between 20-40%. The rule of thumb is that if you are comfortable, the tape is comfortable. However, for long-term storage cooler and dryer is better. Do not freeze tapes.
(2) Use a sealed plastic box or acid-free container to protect the tape binder. Containers should not attract or retain moisture.
(3) Be sure to store your tapes vertically so that the reel hub supports the weight of the tape.
(4) Don't run tape for 24 hours after changing environments.

Storing your analog tape transfers on digital media -- "Perfect Sound Forever"? Well, not exactly ...

It is beyond the scope of this brief article to cover the vast subject of digital archiving. But one thing is clear. You should NOT trust your digital assets to any single digital backup.

Optical digital media (like DVD-ROM) is, in some ways, less fragile than analog tape, but it is not to be trusted as a long-term archival strategy. Once your tapes are transferred into the digital domain, you must devise a strategy for long-term data storage.

However, even if you devise a bulletproof strategy for archiving your digital assets, do not discard the original analog tapes. After three decades of refinement and change, archiving techniques and materials as well as analog-to-digital conversion standards seem to have stabilized. But they could still change in the future. It is possible that further advances in transfer, restoration and archiving technologies will emerge in years ahead. So, continue to store your analog tapes carefully using the above guidelines.

IN CONCLUSION

More questions? We're here to help. Feel free to call us at (732) 303-8559 or email us at info@sonicraft.com.

 
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