There would be no harm in broadening your range to those temperatures.
Actually, RH and temp standards used to be very rigid but it is now
acceptable to broaden them a bit. Most range guidelines are ideal rather
than an achievable reality.  Being in a historic structure it might be more
practical for you to have a wider temp. range since most historic structures
were not designed for tight controls and rely on natural venilation
systems.  What you want to avoid is major fluctuations in temp and RH.  Just
remember that lower temps are good for certain things but can actually lead
to embrittlement as well as paint fractures.
Gretchen S. Winterer
NMMC

On Thu, Dec 11, 2008 at 7:18 AM, Charlie Knight
<[log in to unmask]>wrote:

> I have a question regarding keeping a constant temperature/RH in exhibit
> areas. Our main museum is housed in a mid-19th century Court House (2
> floors) and currently we keep the temperature between 68-72, usually right
> at 70, although some galleries run much higher temps than others. However,
> we have been instructed by our Dept Head (we are a City bureau) to reduce
> our energy consumption to cut our costs - obviously lights can be turned off
> when we're not open, but the temperature controls must remain on for the
> welfare of the artifacts on exhibit. So my question is would there be any
> harm in lowering our temperature by two (2) degrees, for a target range of
> 66-70?
>
> Charlie Knight
> MacArthur Memorial
>
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