i think most people use spray paint? some may use airbrush. i doubt anyone, or at least many, would use a brush or roller. im sure theres weathering tutorials here on tdh but, i know there are many on the mercs sites. layered weathering looks much better and more realistic than topical weathering.
i start by fine sanding the armor then i apply the primer. next i use an aluminum paint rather than silver as it's not as brilliant and beskar is supposed to be duller. next, i either use brush on latex or white toothpaste to mark out the damaged areas. but, not fully, only partially. these are the deep wounds. next, i spray a dull grey and add more latex or toothpaste ove the damaged areas. next, i apply the base color of the plates. then, if theres any markings, i tape them off and paint them. next step, wash off the latex or toothepaste exposing the paint chips, scratches etc... remember, beskar doesn't dent or gouge like durasteel rubbish armor. once dry, i either cover the entire plate in a water soluable/washable black paint and a llow to dry. then, i scvrub off what i want gone leaving behind carbon scoring or, i use use charcoal dust to apply carbon dust to the areas i want dirty. finally, i seal with 3-4 coats of clearcoat. either flat or high gloss depending on the needes of the characters armor.