2 guesses:

King's Jester - 1945

Tiffany - 1931 (has a yellow background not visable in some pictures)

I'm kind of new to the iris world myself, but i'm betting that it's Gnu Rayz.

if you go to www.wildirisrows.com and click on the catalog, then click on the link that brings you to purple/lavender and click on the name there will be a picture. he also gives the height of the plant too.

this is my guess.

Thanks iris gal and ashes of the fire! King's jester and gnu rayz both look close-I'd almost say gnu rayz is closer to the real thing.

The only thing about Gnu Rayz is that it was introduced I think in 1997. How long had your grandmother had this iris, do you know? If iris are like daylilies, they are usually pretty expensive the first few years & only the dedicated enthusiasts get those. The beard on yours looks very orange. How tall is your iris? Gnu Rayz is supposed to be an intermediate iris, so it will be about 25" tall. Tiffany & King's Jester are tall bearded iris so will be much taller.

This is definitely not King's Jester, and Tiffany is unlikely given it's supposed to have a yellow ground.

I agree it's not King's Jester or Tiffany after seeing more pics. That's what I get thinking I can hold an image in my mind!