If anyone has already checked this I would appreciate the info. When
using selenium as a negative intensifier, does it change the curve
proportionally or does it change it non-proportionally?

As I understand it(and my experience seems to support this), selenium
toner used to intensify film can get about 1 grade (0.3) of increased
density. When toning paper, selenium seems to affect the darks
proportonally more than the lights. This would lead me to believe that
using it to intensify a negative would affect the highights
proportionally more than the shadows.

Now I can test this by exposing a negative with a step wedge, checking
it on a densitometer, intensifying it and checking it again. But if
anyone has done this, I like to know what you found.

Thanks