An Arkansas stone does not absorb much oil. Very soft coarse ones might absorb a little. Some are porous, but the pores are very superficial. Nothing like a Crystolon or something which is basically a vitrified sponge.
I think when people use a light source to check for burr remnants they are doing it pretty far along in the sharpening process. At least that is how I do it. FWIW. I don't know anything about wavelengths or microns. YMMV.
A brownie is just something made of chocolate that is in between cake and fudge. If Europeans can't figure out how to to make that taste good then you aren't as good a cooks as I assumed.
For me:
Anything Arkansas (washita-soft-medium-hard-translucent-black)
Anything coticule/bbw
And I really like my Llyn Idwal Grecian Stone, but I have only had one of those to try so can't really make broad generalizations
Also most of the mainstream synthetic water stones.
And diamond stones...
I have had good luck with using my Shapton Pro 1000 for nagura on my Naniwa Diamond 600. I sharpen mostly cheap stainless. I have probably sharpened 200 knives on it in the past year or two. Mostly just edge work, very little thinning. I use a coarse crystolon for thinning. No real sign of wear...
I can't get a clean cut off of the crystolon coarse. Comes out ragged. Haven't tried the medium crystolon. I can get a pretty clean cut off of a coarse India.