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[ARSCLIST] Proper storage of mylar/acetate tapes

A client of mine is moving to new digs and has the opportunity to set up a better storage area for their tapes. This is a collection of 500 or so reels, all have been transferred to a managed digital storage system. About 400 of the reels are old brown-oxide acetate/mylar with a few odd cellulose base in the bunch. The rest are more modern backcoated types (about a dozen were trouble-era Ampex 456 and required baking before transfer).

I read through the following:

AES E-Library: Tape Storage Problems by Radocy, Frank

Imation document

Australian government:


There seem to be some conflicts about the following issues:

1. what humidity level is too low for acetate/mylar? And, what is the true optimum temperature range? The research done in the 50's by AudioTape (ie reaseach done by one of the manufacturers at the time the tape was being manufactured) indicates the 40-50 degrees F recommended in the LOC document may be too cold, especially at low humidity levels. The humidity level recommendations for older tapes seem to be in the 40-60% range, which is easily achievable in the client's new digs, but we want to make sure to get it right so the tapes don't curl any worse over time. My own experience in standard Northeastern US households is that acetate tapes hold up best (ie don't develop edge warp and terrible print-through) if stored in a cool, dry downstairs (with "dry" being, real-world, 60-70% humidity usually, sometimes lower in winter months and "cool" being temp range of about 55-70 degrees F). Obviously we are going to avoid a swinging range of temp and humidity because that is damaging to tapes, according to all research I've read.

2. the temp/humidity levels appropriate for mylar seem a little different from backcoated tapes, but, can the backcoated tapes "live" ok in a mylar-centric environment? In other words, humidity and temp may be a bit higher than sometimes recommended for backcoated tapes. The client could store the backcoated tapes in a separate area, but my thinking is, we know what tapes have sticky-shed and we know they'll need baking before playing in any case. The other tapes are 30+ years stable so unlikely not to be fine under the better-than-before conditions (ie from now on more constant temp and humiditiy).

I should add, we only had one vinegar tape and it was determined that the content was non-valuable so the tape was destroyed. The sticky-shed tapes did have valuable content but I got a very good transfer so it's unlikely they will need to be played again. The client is more concerned about keeping the analog material as a backstop if the digital archive ever fails.

Thanks in advance for your input. I am particularly interested in what storage conditions are being used for large collections of similar tapes.

-- Tom Fine

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