I weathered the trucks on my track cleaning car. I wasn't sure how to go at this but I experimented on a spare wheel first.
First attempt was to apply the powder dry. It didn't really give me the level of color I was looking for.
Second try I added a couple of drops of wet water to the powder and made a paste. It stuck to the metal wheel better so that's what I used on the car.
I applied the mix to the truck and wheels with the small brush shown, and then dry brushed it to blend and even out the color. I will see how it is today. I might have to give them a light spray of clear coat if the finish is not smudge proof.
Bob
