Be especially careful when mixing the ferric oxalate solution from the
powder. I wear a mask and add it to the water in a different room than my
darkroom, the dust is particularly nasty, and shouldn't come near
negatives or prints as it could bleach them. I had a selenium toned
silver print pinned to the wall above the drying cabinet I use to dry to
platinum paper after coating. After a year of printing and opening up
the cabinet to take the paper out, the silver print has become bleached
with only a pale, pinkish image left (I assume this is mostly selenium).
Hope this helps, be careful.
John Rudiak