Greetings,
here is my first attempt to use the Forge World weathering powders on a chaos rhino.
I tried to work according to Forge Worlds
tutorial.
After painting, drybrushing and detailing, I used turpentine to moisten the lower half of the rhino and then sprinkled weathering powder (I used light and dark earth) on the moist area. I tried to sprinkle on a dry area and use the turpentine later, but found that the powder would cling better to a moist surface and that the turpentine dispersed far better when the area was pre-moistened.
After the sprinkling of the powder I added more turpentine to get clumps of powder. Afterward the Model was left to dry for 30-60 minutes - make sure that the powder is completely dried to avoid making very ugly smears of colour (happened to me on the first try). When the powder was dried, I used an old brush to disperse the powder where I wanted it (make smears downward, or blotches where the mud spattert against the side).
Enough with the big text

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here are the results (always before and after the weathering).