RE: [AV Media Matters] metal vrs wooden shelving for VHS tape sto rage

[kbradley@nla.gov.au]

	>Does anyone have data on magnetizing of metal shelving from long
term
	>storage of VHS cassettes?  Any suggestions on how to mitigate?

I did some measurements on metal shelves using a magnetometer to see if
there were any fields strong enough to damage a tape.  The short answer is,
I couldn't find any.

On some of the corners of the folded metal shelves at zero distance the
highest field I have ever found was around 10 oesteds DC, which is about a
quarter of what the Knight article in the IASA phongraphic bulletin defined
as a problem, and about half of what we at the NLA adopted as a minimum safe
standard.  Given that the field strength drops in inverse proportion to the
square of the distance, the actual strength at the first layer of tape is
much much smaller.  So we concluded, that while it is feasable to magnetise
a steel shelf to such an extent that the residual field may be damaging to a
low coercivity tape, no-one is putting that sort of effort in.  I still
borrow a magnetometor and check new shelves occassionally though.

Wood shelves have a whole heap of potential problems associated with exuding
gaseous and other substances which your average conservator can tell you
about.  Metal are a better bet.

Kevin Bradley
a/g Manager: Digital and Audio Preservation Resources
National Library of Australia
Canberra   ACT 2600
AUSTRALIA

Tel:  +61-2 6262-1381
Fax: + 61-2 6262-1653
Email: kbradley@nla.gov.au
NLA home page: http://www.nla.gov.au
Change is inevitable, except from a vending machine

>----------
>From: 	mha@durab.com[SMTP:mha@durab.com]
>Sent: 	Saturday, 1 April 2000 7:33 AM
>To: 	AV-Media-Matters@topica.com
>Subject: 	[AV Media Matters] metal vrs wooden shelving for VHS tape
>storage
>
>Does anyone have data on magnetizing of metal shelving from long term
>storage of VHS cassettes?  Any suggestions on how to mitigate?
>thanks
>mark
>Mark Hopkins + Associates
>28 Warland Avenue
>Toronto ON M4J 3G2 CANADA
>tel: 416-421-5369
>fax: 416-421-7788
>e-mail: mha@durab.com
>
>Monitors Comment:
>This comes up now and then - the short answer -get  Metal Shelves not
>Wood.
>VHS tapes will not magnetize shelving - but people usually ask about metal
>shelving demagnetizing VHS cassettes - that is not an issue either unless
>1. There is a VERY strong magnetic field CLOSE to the tapes for a LONG
>TIME
>2. The shelves have previously been used with rare book bookends that have
>VERY STRONG magnets that will sometimes magnetize the shelving - but
>whether
>the field strength is strong enough to do anything is questionable even in
>that case.
>
>jim