I discovered this site awhile ago on Rembrandt Pastels in it's lightfastness.
http://www.artmaterialsupplies.com/reminfo.htm
The minimum number of years (11 colours) seems to be 25 years in fading. I don't know how accurate this is but would like to hear some opinions.
Also, is there a site that states the lightfastness of NuPastels or Unison?
Sharon: Do you spray the entire pastel painting before framing again?