I'd like to add to what Rick said, all of which I agree with.  Loose
historic windows may be the source of the moisture between the plexi and the
window.  Tightening up the historic windows with help with both insects and
moisture.  However, even in tight window/plexi installations, you may still
get those pesky cluster flies.  I don't know where they appear from
(obviously eggs), but they are virtually impossible to prevent, so
occasional removal of the plexi for cleaning may be necessary.

Marc

American Conservation Consortium, Ltd.
     4 Rockville Road
     Broad Brook, CT 06016
     www.conservator.com <http://www.conservator.com/>
     860-386-6058

*Collections Preservation Consultation
*Conservation Assessments & Surveys
*Environmental Monitoring & Low-Tech Control
*Moisture Management Solutions
*Collections in Historic Structures
*Collections Care Grant Preparation
*Conservation Treatment of:
     Furniture
     Painted Wood
     Horse-Drawn Vehicles
     Architectural Interiors

Marc A. Williams, President
     MS in Art Conservation, Winterthur Museum Program
     Former Chief Wooden Object Conservator, Smithsonian Institution
     Fellow, American Institute for Conservation (AIC)



> -----Original Message-----
> From: Museum discussion list [mailto:[log in to unmask]]On
> Behalf Of Richard L. Kerschner
> Sent: Thursday, January 31, 2008 1:16 PM
> To: [log in to unmask]
> Subject: Re: [MUSEUM-L] Blocking Visible Light to Galleries
>
>
> In response to HHS Director, apparently you are using UV filtering Plexi
> with no tinting. Unfortunately, when UV filtering Plexi or films
> first began
> to be used in historic houses, the word did not get out adequately that
> fading cannot be eliminated just by blocking out UV light. Sure,
> blocking UV
> significantly reduces fading, but visible light continues to fade
> sensitive
> artifacts, especially the high-energy blue light. I know of some historic
> houses that installed UV blocking Plexi so that they could open
> the shutters
> and pull back the curtains to let more light into dark rooms. In so doing,
> the probably did little to extend the life of the collection and may even
> have caused more light damage to sensitive collection artifacts. So the
> standing recommendation from conservators is now to not only
> filter out all
> of the UV, but also filter out us much of the visible natural light as you
> can tolerate (yes, I know, the "black box" concept). How much
> window tinting
> a room can tolerate is not determined by how the view out the windows
> appears. One can see outside surprisingly well through a 90% tint,
> especially if it is a warm bronze color. However, 90% tinting on all the
> windows will make the room very dark inside, so more artificial
> light needs
> to be added in the room to make it work. Even using 50% tinting on the
> windows, which is hardly noticable when viewing outside, darkens the room
> noticeably. Adding back tungsten or halogen lights to accentuate important
> artifacts in the room significantly improves the appearance of
> the interiors
> while exposing artifacts to only a fraction of the light that was entering
> through the windows. We find that several 25 or 50 watt BAB (flood) MR16
> lamps are all that is need to pleasently illuminate our average sized
> historic house rooms. Of course, if you are trying to interpret your room
> historically to including historical lighting that came mostly form the
> windows, this lighting approach will not work.
>
> Moisture between the Plexi and the windows can and should be prevented by
> installing a "P" or "D" shaped silicon gasket on the back side of
> the Plexi
> sheet around all 4 edges. This is the type of gasket that is used to
> weatherproof a door as it closes on the top of the"P" bulb forming a good
> seal. The gasket comes with a self adhesive backing that can
> adhere directly
> to the Plexi, and the bulb seals against the wood stop molding.
> Unfortunately, the bugs are probably coming in through the loose historic
> windows. It is best to restore the historic windows and seal well
> around the
> edges before interior storms are installed. We have found that Mortite
> caulking cord works well and remains reversible, although if the paint
> around the window is flaking, the Mortite will pull it of when it is
> removed. A clear acrylic caulk makes a more permanent and
> invisible seal but
> may not be appropriate for use against significant historic
> interior woodwork.
>
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