Greetings all:

Timothy McShane is correct stating that all light causes irreversible
damage.  

I would caution against installing UV film to the glass of the windows,
especially if it is historic.  I have seen problems with poor installation
(bubbles, incomplete coverage resulting in small gaps around the edges,
etc.); film adhesive failure (resulting in bubbling); problems with window
maintenance (the filmed windows can be difficult to clean unless you follow
the manufacturer's recommendations closely); and breakage of the glazing
when the film needs to be replaced.  At the present time, we don't really
know how long the film remains effective, therefore it will require annual
testing with a UV meter.  Eventually it will require replacement.  I prefer
installation of UV filtering storms (consult with your preservation
architect about how to install them on the windows) and roller blinds with
UV absorbing acrylic.  There are plenty of good filtering media available
that meet the following recommended specification and that will bring the UV
down to less than 10 microwatts per lumen (a vast improvement over the
previously published standard of 75 microwatts/lumen).:  

	Transmission curve normalized at 500 nanometers with less than 11%
transmission at 320 and 350 nanometers and less than 50% transmission 	at
400 nanometers.

I recommend installing window treatments suited to the historic nature of
the building in additional to UV reduction materials, budgeting for their
eventual replacement because they will eventually fail due to light
exposure, and initiating a program to adjust the window treatments to
moderate the light entering the building (our colleagues in the UK National
Trust do this throughout the day in the stately homes of England).
Furthermore, if the historically appropriate window treatments can
completely block the light as well as moderate daylight during the daytime,
these should be used.  If not, you might consider installing light blocking
roller blinds.  Institute opening and closing procedures so that the light
excluding blinds/window treatments are open only when the building is open
to the public.  This will go a long way toward reducing the overall
cumulative exposure of light sensitive objects.  

The websites recommended by Mr. McShane are all excellent and will provide
additional background and recommendations.  If I can be of further
assistance, please do not hesitate to contact me.

Wendy Jessup
Conservator


Wendy Jessup and Associates Inc.
1814 N. Stafford St.
Arlington, VA 22207
(703) 522-2801
FAX: (703) 522-2802


-----Original Message-----
From: Museum discussion list [mailto:[log in to unmask]] On Behalf
Of Timothy McShane
Sent: Wednesday, July 27, 2005 6:57 PM
Subject: Re: Window Shades For A 1910 Structure

Lisa;

Don't forget, even with 99% UV protection, any light will cause damage,
and the damage is both cumulative and irreversible.  Visible light will
bleach, yellow or darken just about any pigment; visible light and the
associated heat will also provide energy to the chemical reactions that
cause deterioration, speeding up the break-down of anything the light
falls on.

This is not to say that blocking out the UV is a bad idea--it just
isn't all that you need to consider, and that "maximizing the light" may
not be appropriate if you are using that space for artefact exhibition.

Here's some websites on the harmful nature of any light;

Northeast Document Conservation Center
http://www.nedcc.org/plam3/tleaf24.htm 

U.S. National Park Service Technical Preservation Services for Historic
Buildings
http://www.cr.nps.gov/hps/tps/technotes/PTN30/introduction.htm 

The McMichaeal Canadian Art Collection
http://www.mcmichael.com/artlight1.htm 

The Northern States Conservation Centre
http://www.collectioncare.org/cci/cciel.html 

The Science Museum of Minnesota
http://www.smm.org/research/Conservation/agents/light.php 

     Cheers,


------------------------------------------------------------
Tim McShane, Assistant--Cultural History
Medicine Hat Museum and Art Gallery
1302 Bomford Crescent S.W.
Medicine Hat, AB   T1A 5E6
Tel: (403) 502-8587
[log in to unmask]

>>> [log in to unmask] 07/27/05 12:22 PM >>>
What about reducing the UV with window film then you don't have to
worry
about the shades doing the job for you.  Check out Llumar films which
claim "Depending on the film selected, LLumar can cut from 12 to 93
percent of incoming light, eliminate 99% of the harmful ultraviolet
radiation
to protect fabrics and finishes, block 92% of glare and cut up to 76%
of
solar heat gain through the glass."  The web address for US
architectural films is
http://www.llumar.com/na-eng/Architectural/building.html.  The plant
is
in our town and the CEO has told me that they feel they block 100% of
UV
but they don't claim it because it is possible to have tiny holes in
the
film that render it 99%.  He said they sell quite a bit of it for
people
who cannot be exposed to UV at all and have to have their windows
filmed, can only go out at night in the dark, etc.

Elizabeth

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