Thanks for the detailed response, Joe.   Lots of people are looking at that Technical Bulletin.  Walter

>>> [log in to unmask] 10/28/03 08:40AM >>>
Cooler and drier storage has been cited numerous times for extended term
storage conditions of magnetic tapes and other archival materials.  ISO
18923 Polyester-base magnetic tape - Storage Practices is one source.  For
a more thorough discussion on the benefits of lower RH and temperature, I
would recommend the CCI Technical Bulletin #23 - Guidelines for Humidity
and Temperature for Canadian Archives.

As for 25% being the "ideal" target, it is not written in stone.  I guess
20-30% RH is the ideal range, but because the ISO standard does not
recommend going below 15%, then 25% seems to be the best target (a bit more
of a buffer to avoid going below 15% because of fluctuations).

Joe Iraci
Canadian Conservation Institute

                      Walter Cybulski
                      <[log in to unmask]        To:       [log in to unmask] 
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                      <[log in to unmask] 

                      27/10/2003 01:50
                      Please respond to
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Mr. Iraci:

Did you really mean to say 25% RH?  Can you cite a source for this?

- Walter Cybulski
Head, Quality Assurance Unit
National Library of Medicine

>>> [log in to unmask] 10/27/03 08:47AM >>>
We have heard some people indicate that it is a good thing to rewind while
others have stated that they have played old tapes that have not been
regularly rewound with no problems.  There is no one answer for every tape
as everyone is aware.  However, as stated by Hannah Frost in an earlier
post, resources are limited and therefore is this a practice that should go
to the top of a resource limited to do list that many institutions are
faced with?  Quick summary:

Advantages of rewinding:

-prevention of interlayer sticking
-debris trapped between layers of tape becoming bonded
-reducing print-through in audio tapes
-retensioning tape pack so that it has the ideal tension

Disadvantages of regular rewinding:

-time consuming and manpower drain on an institution
-if performed on poor quality or dirty equipment it will do more harm than
good (introduce dirt into tape and tape pack will not be ideal after
-overhandling of tape

I believe that if tapes are properly prepared (cleaned and wound to the
correct tension) before going into storage and then stored properly (cool
and dry - ideal about 25% RH and less than 20 degrees Celsius and in a
proper storage container than keeps out dust and debris) then rewinding is
not necessary.   The tapes are clean (which will take care of bonded
debris) and cool and dry storage will deal with the interlayer sticking
because binder degradation is slowed considerably.  If you are concerned
about print-through then this is another issue and perhaps a different
strategy should be adopted.  If the storage conditions are poor (high RH
and greater than 25 degrees Celsius with wide fluctuations) then rewinding
should be considered.  Final comment, are any institutions actually
rewinding tapes on a regular basis?  I would like to hear from people who
know of institutions doing this.  I doubt anyone is doing it every three

Joe Iraci
Canadian Conservation Institute

                      Jerome Hartke
                      <jhartke@MSCIENCE        To:
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                      24/10/2003 05:13
                      Please respond to

Do as you wish. Interlayer sticking is well documented, and can actually
rip out pieces of the magnetic coating if tapes have been stored for a
long time. In addition, any debris trapped between layers can become
bonded over time.

Layers of a pancake are under significant pressure. Some tapes have
severe problems while others do not. You are fortunate if you use high
quality tape, or have never experienced problems. Others who had better
things to do with their time have been confronted with unrecoverable

Media Sciences, Inc.

Hannah Frost wrote:
> At 08:21 AM 10/24/2003 -0400, Joe Iraci wrote:
> >Retensioning on a regular basis in many cases will have no value
> >and in fact may damage tape if the rewinding is performed on cheap
> >rewinders or equipment that is dirty or not properly aligned.
> Not to mention that the process of retensioning a tape archive takes a
> great deal of precious staff time. When you factor in the risk involved
> unnecessary handling, it becomes clear that there are more productive
> things that can be accomplished to care for the collection in the time it
> takes to retension: surveying for materials at risk, grant writing,
> reformatting, and so forth.
> Hannah Frost
> Media Preservation Librarian
> Stanford University Libraries
> > if storage conditions are good and there has not been wide
> > fluctuations in storage conditions, then I don't think it is
> > necessary to retention tapes every three months.