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[AV Media Matters] Relative Humidity, long term
It was good to see Jim Wheeler post, who has had a long career at Ampex. Jim,
thanks for all your papers and writings that line my shelves!
One of the best comprehensive humidity studies was done by Ed Cuddihy of Jet
Propulsion Labs, Pasadena, back in the 80's I think.
His testing indicated almost unlimited lifetime for tapes stored at 20 per
cent relative humidity, and at a cool environment, which if memory serves was
40 degrees Farenheit. His concern was instrumentation tapes, but the
materials are similar in the other products. It is the old issue of binders,
and plastics used in media manufacture.
The only thing Glen Schulze and I have seen in operations at Denver's low
humidity, in winter, of 10 per cent or lower, is sometimes brown stain will
form on heads from some instrumentation tape. We have also observed this in
my recording lab here in Austin. Both buildings did not have local control of
humidity, but since the low humidity here in Austin is often only a week a
year, we have lived with it during operations. Aggressive head cleaning
removes this signla reducing brown stain effect. You have to use strong light
and magnification to see brown stain on heads, but its signal loss on known
test signal levels is the first clue we have to its appearance in winter.
Another reason to have well documented test tapes!
We wish we could find better storage than using off site vaults, but that has
been our local solution, until finally we got auxilary freon air conditioners
in the recorder lab, to augment the chilled water central system. By forcing
the freon units to do the majority of cooling, they wring out the mositure in
the lab. (The mixing coils of chilled water units may be located elsewhere in
a zoned system and not able to control local humidity to the degree needed by
AV operations.) With a couple of freon units, we too can keep the humidity
down while one air system or the other is being overhauled. I heartily
endorse this dual system to anyone having valuable AV masters to protect and
run in a working lab environment.
Subjectively, I have noticed less of a humidity problem with various video
tape media than the reel to reel tapes had over the years. The removal of
natural lubricants such as whale oil from reel tapes, seemed to increase
instances of sticky tape problems over time. These were the binder failures
that have appeared from time to time. Long term storage of reel tapes without
rewinding can lead to amines forming in the pack, and suggested rewinding
exercises relieve both storage induced tape creep, and air out any outgassed
components of binders.
Amines are the strong odor you will find around tapes suffering binder
degradation. Once you smell it, you will be able to "grade" your archives by
the nose test!
Other stiction tests over time will help you keep aware of your media
archives conditions. The most simple of these, is allowing reel media to
unwind a few turns by gravity, and look for layer to layer adhesion before the
strand comes off the layer below it.
Lots of good information coming over this list. I have however, had some
problems of trying a simple reply to mail locking up my computer for this list
only! Anyone have an idea about that? I am using a Mac Quadra and Microsoft
Mail, an oldie but goodie.
ARLUT Recording and A/D Lab