I think it has been brought up several times that
certain colors in paints such as brown and yellow
tend to show worse degrees of fading.  I've seen
this happen to cels that were very well taken care
of.  Also, some series seem to show more fading
than cels of the same age.  Of course, I think
research into this would take someone with a much
greater chemistry background than the average
person and perhaps a greater knowledge of which
series used which products to produce their cel
art.  The best most of us can do is just report
through observation.

Keys