A local anime shop that I've "lived in" for years
(I love those guys) have quite a few cels 
framed on their walls that have been up there for
at least 6-7 years.  They also have flourescent
lighting O_o (BIG no-no for cels!!)...

One of the most painful examples to look at
is a Sailor Moon cel.  It's from the very
first episode when Usagi's mother is holding
Usagi's failing test paper and scolding her
for it.  Usagi has her usual pained expression
and it's a great image, very recognizable by
any SM fan.  Unfortunately, this is one of
the cels that has been sitting on the wall under
the flourescent lighting - and ALL of the
trace-lines (black outlines) are GONE.  It looks
like one colorful blob of paint.  It actually
now resembles what the BACK of a cel looks like...
which is heartbreaking as I remember how good
it looked years ago... they also have a DBZ cel
of chibi Gohan powering up that would be awesome
if it had any trace-lines left, too...

Absolutely heartbreaking to see... =(

Kim
aka Lady Zatara