Silly me - I totally forgot to test RB Deep Black on Ivory to see if it webbed or not!
Here you go, on Eff. Ivory (Light and Dark, I was using up ends). Got it hot enough to swirl a little - so a little bleeding into the ivory - but that is a function of the heat, I think. No webbing, crawling, or effects. (Bear in mind, I really like those effects - but it's so nice to have options!)
So, like the Belladonna Black Diamond - here we have another black that can be used as a black without thinking about odd reactions.
I think that the Reichenbach might be a little blacker when used very thin - but both are completely excellent!