Barbara Applbaum's GUIDE TO ENVIRONMENTAL PROTECTION OF COLLECTIONS and
Gary Thomson's THE MUSEUM ENVIRONMENT are excellent aids to understanding
how the environment affects artifacts, but they are not repair manuals.

You mention that you have two hygrometers; do they measure humidity only,
or are they hygrothermographs (recording temperature and relative
humidity)?

Temperature is measured using a bimetallic element which is pretty
bulletproof; humidity is typically measured using hair bundles.  Hair is
responsive to changes in moisture and this attribute is used to move a pen
or ink reservoir up and down along a moving paper chart; the bimetallic
element does the same thing in response to changes in temperature.

The problems with hygrothermographs are mainly related to the hair bundles
which respond to changes in moisture.  If the hair bundles are exposed to
pollutants and/or wide changes in %RH, they go out of callibration.  This
means that these machines need regular callibration and that requires
another device, the sling psychrometer (or a battery operated
psychrometer).

The mechanisms are fairly simple and it is not difficult to make them work;
the fun comes from making certain that the readings are reliable.  If the
pens are dry, replace them.  If the ink boats are dry or corroded, clean or
replace them.

The bimetallic temperature portion should need no work beyond callibration
against a callibrated thermometer.  The hair bundle(s) need to be "washed".
By this I don't mean removing the hair bundles and running them through a
sink.  The hygrothermograph should be enclosed (a big garbage bag will do)
with a sponge full of water to create a 100% relative humidity environment
inside the bag.  After a couple of days the hair should be relaxed enough
to read 100+ % humidity and many pollutants should have "washed" out.

Relative humidity changes quickly.  When opening the "environmental
chamber" do not waste much time in adjusting the hair bundle to read
correctly.  If you are doing this in the middle of winter with gas central
heating which gives very low levels of relative humidity the hair bundle(s)
will quickly be exposed to an extreme condition which will make subsequent
readings suspect.  See data loggers, below.

I have two hygrothermographs in the lab.  One has one hair bundle and the
other has eight bundles.  I also have a battery operated psychrometer.
Those date back two decades and they are not much used.

About ten years ago I began using data loggers.  I have two which are
Macintosh readable and one which is PC readable.

The Mac machines (DataBear) were purchased from Langan Products, Inc.  2660
California St, San Francisco, CA  94115   (415) 567-8089  (voice/fax).  I
paid about $800/unit then.  These days, cheap PC loggers are available from
about $100 and up.  I still prefer the DataBear because it is accurate over
a far wider range of relative humidity than any other logger I've tested.

So, I advocate putting recording hygrothermographs into museum storage as
curious artifacts and putting data loggers on-line.

The benefits are many.  The data are logged at intervals set by the
operator at a computer; the data are recorded in digital format (no more
wandering around and finding a hygrothermograph with five weeks of data on
a one week chart...) and can be downloaded to a spread sheet or
statistic/graphic program giving weekly, monthly, annual, or.... charts.
Far easier for administrators or boards of directors to understand when you
come before them pleading for environmental control.

Hope this helps,

Jack


>I recently started a collections initiative to determine the
>environmental status of our collections storage and exhibit areas.
>The Museum's two hygrometers are in varying states of disrepair.
>I'm looking for a comprehensive resource to accomplish the repair
>and daily operation of these simple to take apart but not so easy
>to put together instruments. I have heard that Barbara
>Applbaum's GUIDE TO ENVIRONMENTAL PROTECTION OF COLLECTIONS and
>Gary Thomson's THE MUSEUM ENVIRONMENT are both excellent choices.
>Does anyone have any opinions about these publications or others
>I might be able to get a hold of?
>
>W. Parker Hayes Jr., Curator
>Airmen Memorial Museum

Thompson Conservation Laboratory
7549 N. Fenwick
Portland, Oregon  97217

503/735-3942  (voice/fax)

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