Thank you, Ma'am!
I will certainly look into that when I am next buying supplies. I do a lot of panel-line on WWII era stuff with a pencil, which will stay black if gone over with matte coat (otherwise it can glint silver at certain angles, or with dilute paint applied and wiped immediate. I have taken a shot at an oil wash, and it seemed a lot of work for the result. What seems attractive about this is the claim it can go over a matte surface.