Weathering powders are mostly used dry. They stick very well to matt surfaces. The powders are an imitation for rust, dirt, sooty and dust. Use a paint brush to apply the powder on the surface of the model. If you use an old paint brush and cut back the hairs so that 5mm of bristle remains. You can apply the powders by stippling. You also can mix the powder with terpentine. Apply the mixture with a large brush on the surface of the model.