In July 05 I started an informal, lazy lightfastness test. All I did was take a few different print samples, cut them in half, and tape one half to a window that gets skylight all day long and a couple of hours of direct sun each day, simulating nightmare conditions for work hung on the worst possible wall. The other half is in a dark flatfile drawer for comparison.
1: a stepwedge printed with piezography warm neutral inks with the portfolio black ink (non archival pigments added to the darkest black) on Hahnemuhle photorag
2: same, but varnished with Golden Paint aqueous UV blocking varnish
3: a silver print on Forezo, toned in selenium and nelson gold
4: a platinum print on an unknown rag paper
5: a c-print from the drugstore, printed on Kodak Royal paper
Results from a year or so ago: no changes on either of the ink prints or the silver print, other than some scuffing on the unvarnished ink print. virtually no change on the c-print (this was the biggest surprise). slight yellowing of the paper on the platinum print, but no change to the image.
Changes as of today:
-no change on the varnished ink print.
-very slight lightening of the darkest square of the unvarnished ink print. it might be due to scuffing against the glass. it's barely perceptible when viewed under plexiglass right next to control sample.
-the c-print has finally gone to pieces. It's faded a bit and taken on a pronounced yellow cast
-the platinum print's paper has continued to yellow. it's not objectionable, but noticeable compared to the half that's been in the dark. the image is still unchanged.
-the c-print's paper, on the other hand, has gotten a bit brighter. it seems to have been bleached a bit by the sun. no noticeable changes to the image.
Samples are back in the window; I'll try to remember to look at them in another year or so.