Totes not trying to monopolize this epic thread, but I just started something out of necessity & it works surprisingly well.
Gouache for the first layer of grime (4th+ layer of background shading basically)
I do art stuff pretty much as often as I’m able (which has been a bit more of late 
) & is why I happen to have Gouache just lying around. I used it on the KT & BB as well and it’s working out surprisingly well. A water mixdown is needed followed by buffing it down however you want.
I used to use oils for this on an upper layer, but I’m finding this works a bit better cuz it dries - but! add water & its malleable again 
. I would likely still use oil for accents on a by project basis, but this is a new use for Gouache I’d never thought of before.
