Re: [AV Media Matters] Relative Humidity, long term

[tomliew@talkevax.ucsd.edu]

I agree with Stuart that many good things is comming on line.
e has tickle me on a few of the areas of my research..particularly
brown stain that are observerd on tape heads operating with  particulate
tape under extremely low humidity.

>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.
>

Temperature can help but too low a temperature can cause problem in
the lubricant  segregating out of the binder. You might want to
check out http://oldsite.nta.org/MediaStability/ on the subject of
storage and life-time.  There is a very good study by John van Bogart.

>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!

Brown stains are not only brown but can also be blue. It is easily
seen under optical microscopes.  It is almost certain taht the only
way to remove them is  by using an abrasive tape.  Solvent and Q-tip
is no use.

Tom Liew

>