Mr Soeborg was nice enough to create a new thread in this forum here with some info concerning his varnish/powder mix, which he states should be the consistancy of thick paint.
Fair enough, I’m thinking latex house paint thick - NOT Drylock water-proofing thick. Hopefully I’ll be able to experiment this weekend.
Actually, having an old Athearn PS covered hopper (and powder chalk, and rust paint, AND cosmetic sponges from some other modeling project), I should try the other techniques mentioned in this thread too (except the brunt sienna artist oil drop/drag down with turpentine-laden brush - never got that to look good)