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Re: [BKARTS] questions re: exhibiting manuscripts



This is a really interesting question, I think.  I don't recall ever
reading about this concept in conservation lit.  Since I'm neither a
physicist nor an optics expert, my comments are just musings-
I can remember burning all sorts of things (insects, matches, paper) as
a kid with magnifying lenses.  I recall that it took a very sunny day to
get the necessary energy focused through a lens to even start the item
smoldering.  If we assume that in a properly planned exhibition, the
light source is much less bright (50-80lux versus well over 80,000 on a
sunny day) then chances are that even with magnification, the energy
can't be pumped up enough to cause flames.  As said, I'm not quite sure
how optics increase/decrease light intensity.  There's also the matter
of the intermediary plexiglas case or frame glass distorting things
(refractive index). 
One simple solution would just be to put a lux meter in the case and
focus the lens on that, and get a reading.  I suppose a physics lab with
a student in need of a research project could set up a 'manuscript' of
photovoltaic cells, have the electric signal 'translated' to a visual
interpretation on one's computer, and then watch the changes in electric
signal as light passes over it.

Aside from actual burning, there is a more realistic concern about
fading.  Investigations have been carried out with the camera flash
concern, and have found this to be much of an urban myth.  Where this
policy still exists, it is often because flashes can be distracting,
rather than damaging.  I have a feeling that the magnifying glass
concern, when looked into, will amount to much of the same.  Twenty
people an hour focusing a magnifying glass on the same 2mm spot (the
chances of which are very small) for a fraction of a second per person,
will only be equivalent to a minute or two of extra exhibition lighting
over the course of a show.

Doug Sanders
Conservator
Indiana Historical Society

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