Every year, as cold weather approaches, we get questions concerning harp care. Unfortunately,
once cold weather really sets in, we get repair work made necessary by the effects of cold and
low humidity. Hopefully the following will provide useful guidance that will prevent some of
The two factors affecting harps in cold weather are relative humidity and temperature.
Normally we see more issues because of low humidity. This is because wood is hygroscopic;
it absorbs moisture from damp air, and gives it off to dry air. When wood absorbs moisture
it swells. Conversely, when it gives off moisture it shrinks. The finish on a harp slows the
rate of transpiration, but does not stop it. In winter, when a house is heated, the relative
humidity will drop to very low levels, especially when the outside air is very cold. Under these
circumstances the wooden structure of a harp will shrink. Since the wood is constrained by glue
the shrinking wood will crack along the grain.
Gilded harps have an additional problem. Under the gold is a material called gesso, which
is a mixture of powdered chalk and animal hide glue. It provides the necessary smooth base
for the gold. Gesso is actually as hygroscopic as a spruce soundboard. It is also more fragile,
and prone to crack and chip off when exposed to very dry conditions. Gold harps are very
unforgiving of low (under 45%) relative humidity.
To prevent damage from low humidity the harp should be kept in a room where the relative
humidity is above 45%. If the harp is gilded I recommend a minimum RH of 50%. Brief
excursions into dryer places for concerts, etc. are not usually a problem because they last only a
few hours, but do avoid leaving your harp in a hot, dry room overnight.
Cold presents an entirely different problem in that the structure of the harp is really unaffected
when the instrument gets cold. The issue is the finish. Unless your harp is finished with
shellac, often called French polish, the finish will shrink as it gets cold. Wood does not shrink
significantly in response to temperature. This means that the finish will try to shrink over the
unyielding wood,and since it cannot, it will crack or craze. If your harp stays above 32F (0 deg
C) there is usually no problem, but if left in a car overnight when the temperature dips below
freezing there will certainly be some interesting texture to your finish the next morning! I
personally do not let my harps stay where they might be exposed to temperatures below 40F for
longer than a few minutes.
To put the above advice into perspective, a guitar-maker's tip published by a respected firm
tells one that a crackle finish on a solid-body guitar is achieved by applying two or three coats
of lacquer and allowing it to completely dry. The guitar body is then placed into a freezer fro
a few hours. Whwn it is removed from the freezer it will have a crackle finish that can then be
sealed with another light coat of lacquer. So if you want a crackle finish on your harp, just let