Hair bundles for hygrothermographs

Helen McPherson <hmcpherson [at] slv__vic__gov__au> writes

>We have a range of drum hygrothermographs ( thermohygrographs in our
>part of the world), including battery and clockwork models, Nikkei,
>Sato Sigma, Izuzu, Ogawa Seiki and Michromech. Depending on the
>machine location, they run on 7 and 31 day cycles. The machines are
>recalibrated using an electronic hygrometer, each time the charts
>are changed. The hygrometer is recalibrated inhouse every 12 months.

In my experience, all brands of these machines are the same. Some 20
years ago, we (at that time, at Westpac Archives) were given the
same advice re: weekly wetting of the hairs with distilled water.
The technician / sales rep. also told me there were two unrelated
kinds of relative humidity, those in physics books, and those
measured by their machines.

While I accept there may be some logic to wetting, I thus ignored
it. I have also been informed Asian hair has commonly been used
because it is straight; seems tidy.

I have calibrated and used these machines over 20 years, without any
special treatment, and find them mostly accurate over the medium
humidity range, say 30%-80%. Whenever tempted to replace hairs, just
because they were old, I was confronted with an usurious replacement
cost; I thus ignored it, and the machines still seemed to cover the
same RH range just as accurately. When, through the fortunes of
life, I entered private practice, and thus was responsible for my
own fortune, I happened upon a free thermohygrograph, sans hair.
Lacking the luxuriant locks of my youth, I seized a lock of my wife
(and colleague)'s curly hair, washed it in non ionic detergent,
rinsed in distilled water and fixed it in place. It looks a little
odd, but, calibrated, works just as accurately on regular charts.

I have always seen a potential problem with the build-up of
hygroscopic salts on such hair. I do not know if the principle of
wetting hairs was meant to deal with this. I know whenever I applied
this principle, RH reading was quite unstable for weeks.

In short, I too have happily used these instruments, pondered their
mysteries.

James Elwing
Elwing and Gurney Archival
Lawson, NSW, Australia


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                  Conservation DistList Instance 16:24
               Distributed: Thursday, September 26, 2002
                       Message Id: cdl-16-24-005
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