The only prints I have on platine I made at a workshop taught by Clay and the sheets of platine I used were marked as being pre-treated in oxalic acid.
Sandy, I will have to try some of my stonehenge w/o the oxalic treatment. I noticed the graininess in the highlights, too, but thought it was just a characteristic of the paper.
Any suggestions on whether or not to pre-treat Lennox paper? I think I am going to pick some up to try next time I am out in Dallas. If it works out well my paper cost is going to drop big time! $1.89/full sheet Lennox; $11.99/50 sheet pad of 8.5x11" Clearprint Vellum.