What do you do if a valuable master tape that you've had on the shelf for the past 15 years tries to weld itself to the playback head as soon as you try to play it? Swear loudly, then pop it in a low oven, advises master chef JEAN‑Paul White...
You may have read about a tape problem dubbed 'sticky shed syndrome', but it's not until you try to play back a tape afflicted by this condition that you realise how serious it is. Oxide sheds at an alarming rate, and what's more, it sticks like glue to the heads and tape guides. The first thing you notice is a physical screeching noise [even when you're not listening to Celine Dion — Ed], as the moving tape is 'bowed' by the contaminated heads or guides, and this physical modulation transfers itself to the audio. The top end is usually dramatically reduced, and after just a few minutes of play, the friction may cause the machine to grind to a halt. On occasions, the tape actually sticks to the heads, and pulling it off can dislodge more oxide, increasing the risk of irrecoverable dropouts. We're warned often enough about the problems created by storing tape inappropriately, but in my case, these reels of Ampex 456 had been stored in a dry domestic environment at nominal room temperature, for around 15 years. There are better storage conditions, but on the whole, I'd expect a 15‑year‑old tape stored in this way still to be playable, so what went wrong?
Whale's Revenge
At least part of the answer lies in that great '70s crusade, to 'save the whale'. As a result of the environmental lobby in the US, tape manufacturers Ampex were stampeded into abandoning their traditional whale oil tape‑binder (the binder is the material used to fix the tiny particles of magnetic oxide to the tape's flexible backing tape). Ampex's synthetic substitute, perhaps because it was formulated without the normal research and development, has since undergone some form of chemical breakdown, and at the same time, absorbed moisture from the air. The problem was identified, and improved formulations substituted to clear the problem, but that still left thousands of reels of tape around the world that were literally rotting away. What, if anything can you do to recover material archived in this way?
A few years ago, several articles and papers were published on the subject, and the general consensus was that baking the tape at a precisely regulated temperature for between 12 and 24 hours would drive the water from the binder, making it stable enough to play. The baking temperature quoted was between 50 and 55C, so before I could put these methods to the test, I had to find a suitable, temperature‑controlled oven.
Counting Chickens
Having asked around, a friend of mine said he could borrow an incubator of the type used for hatching eggs, and as it turned out, the temperature control system could easily be set to 50C. A thermometer was placed inside the unit to check the temperature, and then the worst of all my archived tapes was placed inside. Inside the incubator is a fine wire netting shelf, so I put the tape directly on this and left it to cook for 24 hours. If you haven't seen an incubator before, it is simply a box fitted with a thermostatic heater. There's a perspex lid with a small hole in the centre, which allows air to flow through the box, and small holes in the base allow fresh air in. Because part of the job of baking is to drive off any moisture, you should leave both sets of holes unobstructed.
Don't attempt this with a domestic oven, as the thermostat doesn't go low enough. Microwaves are right out!
After 'cooking', the tape was removed, allowed to cool for ten minutes and then threaded up on my freshly‑cleaned Tascam 32. Aside from a few minor dropouts near the start, where the tape surface had been damaged by previous attempts to play it, the tape played back surprisingly well, with no trace of sticking. The heads were also reasonably clean afterwards. I transferred the entire contents to DAT without any additional processing (apart from a little help from a plug‑in Waves Q10 equaliser to freshen up the top end), so that I could clean it up later using Sound Tools and DINR.
Having made the process work once, I went on to treat the rest of the tapes in my collection, just to prove that the treatment wasn't a fluke. With the benefit of hindsight, there are a few rules you should follow if you find one of your tapes suffering from sticky shed syndrome. Firstly, and most importantly, don't continue trying to play an affected tape once you realise there is a problem: you could cause more damage than the sticky shed syndrome itself. For example, if you pull large chunks of oxide off the tape, you're bound to get dropouts. If the recording is commercially valuable and the tape is Ampex, then contact Ampex (see 'Call The Experts'). If you're doing the job yourself, the next step is to put the tape back into normal storage, until a means of baking it can be found.
Dogged Determination
The incubator seems the ideal way of heating tape, but it is important that no part of the tape is in direct contact with any metalwork or any part of the heater. The wire mesh shelf is ideal, as it allows for even heating via the warm air in the box, and not via conduction. Check the temperature of the baking system to ensure that it stays stable within the 50‑55ºC range, and simmer for 24 hours. Don't attempt this with a domestic oven, as the thermostat doesn't go low enough. Microwaves are right out!
After cooking, play the tape as soon as it is cool, and take this opportunity to replace any dodgy splices that may have dried out over the years. Once you're happy the tape plays OK, clean the machine again and transfer the recording to your preferred medium — and if it's digital, make sure you get as high a level as possible without clipping.
Growing Old Gracefully
The rather short history of the cobalt‑doped iron oxide tapes used for DASH, Pro‑Digi and ADAT suggests these tapes resist degradation in humid environments rather better than some analogue audio mastering tapes. Higher technology digital tapes use metal particles (MP) instead of iron oxide, as their magnetic component. The tendency for such finely divided iron particles to oxidise in microseconds when exposed to air tended to create pretty firework displays in development laboratories. It was feared this strong tendency to oxidise, albeit at a much lower rate, would limit the life of MP tapes.
In the event, MP passivation techniques have been developed, so that well‑chosen MP has a similar life expectancy to that for other tapes. When considering the relative merits of analogue versus digital recording formats for archiving, remember the phrase 'analogue degrades gracefully' and that, while storage space costs money, a 'chunky' format with wide tracks tends to be inherently more robust then its more compact brethren.
Finally, try and make an educated guess what machines, and spare parts for them, will be around to play back your masterpieces 20 years hence! Justin Underwood
Call The Experts
Quantegy Europa (or Ampex, as they then were) established a UK facility for heat‑treating open reel tape in 1983, and have carried out the heat treatment process ever since, free of charge, at various locations around the world. The procedure usually starts with a telephone enquiry from a tape user. The enquirer is then sent details, including the address of the UK tape distribution centre, where heat treatment is carried out, and a 'Release Form'.
The Release Form is an acknowledgement of the incalculable value of many of the masters passing through the process. It carries a statement that Quantegy will take every practicable care of customer's tapes, will use its best efforts to restore them to playable condition, but cannot accept responsibility for damage or degradation due to accidents such as building fires or the like. Quantegy's legal department requires that the Release Form be signed by the tape owner, or person primarily responsible for the tapes, and that the signature be witnessed, before processing starts. No charge is made for processing, but the customer is expected to pay the transport costs (both ways). Justin Underwood, Product Manager, Quantegy Europa.
Following Footprints
When an old tape is taken from storage, there is a risk that softening of the coating may have caused layer‑to‑layer adhesion in the wound pack. Ensure a recorder known for gentle tape handling is used, and that a tape op, or other competent person, stays close to the recorder while the tape unwinds for the first time. If significant layer‑to‑layer adhesion has occurred, clicking sounds will be heard as the layers are pulled apart. In such a case, there is a risk that some of the magnetic coating may be adhering so strongly to its adjacent back‑surface, that lumps of coating are stripped from the front coat! If such 'sticky clicking' is noted, it is probably wise to heat‑treat the tape before attempting to unwind it. An 'if in doubt heat treat it before doing anything else' approach also has the advantage that any print‑through resulting from heat treatment is in the same footprints as the print‑through due to long‑term storage.
There has been some confusion as to how long tapes remain playable after treatment, and whether repeated treatments are effective. Tapes should replay satisfactorily for at least three months after treatment if they are kept in a low‑humidity environment. If kept in, say an airing cupboard after treatment, they will probably remain playable for ever! The heat treatment process can be usefully repeated. If tape has degenerated after the first treatment, it can be restored again by a second, or subsequent treatment. Laboratory testing of 1980‑vintage 456 tape included 14 cycles of accelerated ageing and recovery by heat treatment. Degradation to a non‑playable condition and restoration to playable condition was demonstrated for each cycle. Justin Underwood