Add to this mix a very varied collection housed in a historic structure, as is typical of almost any historic house museum.  Aware as we are of the recommended levels and fluctuations, in reality it becomes a question of constant adjustment and being ever alert to the actual conditions in a
given season, weather period, or sometimes day.  Saying "72 degrees" is all well and good (for at least some of the collection at any given time), but when the alarm system is disarmed first thing on a humid summer morning and the house is opened, and condensation is pouring (literally
pouring) off the exteriors of windows to the great detriment of sills and muntins, judgment has to be employed as to nighttime settings and happy--or at least expedient--mediums.

Carolyn Breedlove
Executive Director
Kent Plantation House
3601 Bayou Rapides Road
Alexandria, LA  71303
318/487-5998
[log in to unmask]

Timothy Vitale wrote:

> 72F 50% RH is standard flatline conditions.  Almost no one can maintain
> this outside of a sealed case with major mechanical attached.
>
> 72F +/- 5 & 50%RH +/-5% was standard for 50 years.  In UK and some other
> European countries, 68F +/-5 & 45/55% RH +/-5% is common.
>
> Storage of photographs has been moving to colder and less humidity
> because of there sensitivity to water in fading and acetate base
> degradation.  Big problem with acetate film now.
>
> About 5 years ago Marion Mecklenburg and co-workers (at CAL, SI, now
> SCMRE) stunned the Museum/Conservation world by saying one could go as
> far as 72F +/- 20F & 50%RH +/-20%.  He was talking about storage of
> airplanes at the proposed, SI, Dulles Airport, NASM building.  The
> rational was that the moisture content changes, produced in the
> materials by the 40F/40% range, did not exceed the plastic regime of the
> mechanical properties, of "most" air/space museum materials.  Problem
> was that this is a general statement and doesn't consider materials
> which have tolerances inside these general ranges.  One, I know quite
> well is albumen prints which fracture with a 5-10% RH change.  Already
> flaking paint and very old paint, paper, leather, veneer, etc., which
> have become brittle over time (lost their plastic component), fall into
> the sensitive category.
>
> So we are re-evaluating T/RH standards.  Mecklenburg will be taking
> another shot at explaining his position at the annual AIC meeting
> (Conservators) June 2000.  Most are skeptical.
>
> I say +/-10-15% for non-critical "museum" materials and +/- 5% for
> critical stuff.  RH set point can be slowly adjusted down to 40 %RH in
> winter to protect building which reside in freezing conditions and up to
> 55% in summer for humid climates.  The key is slow adjustment (a month)
> from one set point to another.  There is still significant debate and
> many bruised professional egos on both sides.
>
> Tim Vitale
> Preservation Associates
> 510-594-8277
> 440-775-7331 until 9/26/99
>
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