Today I added explicit references to page nos. in Hayes' Late Roman Pottery [worldcat] to the GRBPIlion page for African Red Slip.
That's hardly worth a post. But I did re-look at the photographs so here are a few excerpts that show variability of surface treatment.
The exterior of an H32/58 of the late 3rd/early 4th AD. Shows thick unbrushed slip on surface. The photo is a little washed out, overall color of the vessel is "normal" ARS orange.
The interior of a similarly dated H53a. Thick, somewhat smoothed surface with feather rouletting.
It would be really nice if I had a good photo of a very smooth H50. I'll look for one.
Interior of an early 6th century H87b. Less detail than the previous two. Thick smoothed slip.
Exterior of the same piece. Obviously thinner slip is "streakily" applied.