some manipulation of the frame.^31 The Rijksmuseum boxes also proved
effective when monitored with humidity indicator strips or small hygrome-
ters, all of which indicated a stable RH within the boxes in the museum
environment.
Extensive studies undertaken by Richard have confirmed that tem-
perature changes affect panel paintings much faster than do RH variations
(Richard 1994). Although he concludes that silica gel has no effect on the
temperature changes, he nevertheless recommends that the gel remain in
use for microclimate boxes. Drawing on the assumption that virtually all
microclimate boxes leak, Richard states that silica gel plays an important
role in stabilizing the RH in display cases used in unsuitable environments
for extended periods.Microclimate boxes without added buffers
Amore recent approach to the construction of microclimate boxes relied
on the hygroscopic behavior of the wood panel itself as a stabilizing factor
within a small volume of air. Such boxes were not kept at a stable RH
through added buffers but instead maintained their own internal moisture
equilibrium at changing temperatures.
Acritical approach to the consistently recommended use of a
moisture buffer in small display cases was presented by Ashley-Smith and
Moncrieff(1984). Their experiences in the Victoria and Albert Museum in
London showed that the silica gel in a showcase neutralizes the short-term
RH fluctuations but does not compensate for seasonal changes. Ashley-
Smith and Moncrieffconcluded that for wooden showcases, silica gel gives
poor results in relation to the time and expense required to purchase, pre-
pare, and handle it, as well as to design and build showcases to accommo-
date it. They stated that an ordinary showcase without silica gel fares
nearly as well—or as poorly—in reducing short-range fluctuations. The
same conclusions were drawn in reference to some old-fashioned walnut
cases in the Royal Ontario Museum, Toronto, that proved remarkably
effective in slowing moderate fluctuations ofRH (Phillimore 1979). For
best results, a well-sealed case made completely of metal and glass or plas-
tic is usually essential (Brimblecombe and Ramer 1983). However, for the
Victoria and Albert Museum, wooden case vitrines serve in themselves as
useful, additional buffers (see Cassar and Martin 1994).
Also in the early 1980s a special type ofmicroclimate box was
created by Padfield, Burke, and Erhard (1984). A cool-temperature display
case was made for a vellum document placed in a close-fitting airtight con-
tainer. The document required a stable temperature of 6 16 °C, some six
degrees cooler than the gallery, and an RH of 40–50%. The box maintained
a nearly constant RH after cooling; however, special care was necessary to
minimize temperature gradients. The case performed satisfactorily for one
year with no change in internal moisture content.
The simplest method possible was chosen for displaying this
document. It was sealed inside a thin, airtight container that was cooled
by means of the Peltier effect.^32 The refrigeration system of the box con-
sisted of two coolers at the bottom of the aluminum tray holding the
microclimate box.
Aclose-fitting, airtight enclosure has many advantages for the
temporary exhibition offlat pieces ofvellum or paper. It can be designed
to maintain a nearly constant moisture content and a safe RH. At room508 Wadum