First of all paint the model with a dark colour or the base colour you want to see underneath the scratches. Then apply a layer of this product onto the area you want to work with either simply using a brush or an airbrush. Finally apply acrylic paint over the area where you applied this product. This will be the outermost layer of paint. Once that is dry to the touch dab the area with water using a brush to activate the product in between the layers of paint to make small highly realistic damage chipping and scratch effects on the outermost layer of paint. These effects can be created using a sharp tool or the brush itself.