Rustall is a rust colored pigment suspended in an alcohol carrier. It is brushed over painted model parts to give them an overall rusty sheen. The rust can be built up by adding more layers of the Rustall liquid, but be sure to let each layer dry thoroughly. A more mottled and random rust appearance can be achieved by building up the layers only in certain areas of the model. Rustall seems to work over most paints, but I've had it dissolve the inexpensive craft-store acrylic paints, so always test it on the paint you're using before applying it to the model. Also, when applying Rustall only to a part of the model, be sure to feather out the edge of the Rustall layer to avoid tide marks. Rustall definitely has a place in the modelers weathering arsenal.