Scale models are intended to portray the original version of a subject, be it a car, tank, plane, train or ship. Rarely will you see a real tank or ship without rust or chipped paint. Cars and planes have stains from exhaust or fuel spills. Models can be finished to exhibit the wear and tear of the real thing. The process of making a model look old and used is called weathering. The most common methods of weathering a completed kit are dry brushing and washes, two easy painting techniques.
Both of these techniques are used after the piece or model has been painted and had decals applied. It is also a good idea to consider the paint types used. Use an acrylic or water based paint for weathering. If the finished model was painted in a water based paint already, make sure it is well cured before weathering. An enamel or solvent based paint used to finish the model kit will not be harmed by using the water based paint in weathering.
The first technique, dry brushing, is applied using a paint brush with moderately stiff short bristles. Dip the brush in paint then dab most of the paint off on a rag or card. Only trace amounts of paint should be left on the brush. Quickly and lightly flick the brush tips over the raised feature of the kit to highlight the detail.
A common use of dry brushing uses silver or aluminum paint on raised detail like rivets, metal framing or radial engine pistons to show worn or chipped paint. A flat dark red or rust color paint can be dry brushed over exhausts on inline aircraft engines to show rust or heat damage. Black can be lightly dry brushed on the model to show exhaust staining or powder stains from guns.
The second weathering technique is the opposite of dry brushing and is the application of a wash. Soft bristle brushes of varying widths are used to apply a wash to the finish of the model kit. Washes are made by thinning the acrylic paint to a watery consistency. Load the brush with the color paint for your wash and then dip the brush in water to thin.
Apply the wash and let the watery paint run into recesses on the model like panel lines or the grooves among wood planking. Washes accentuate these recessed areas. Any excess can be quickly dabbed off. Broad washes are used for general staining such as from spills of fuel and other liquids. The broad wash lightens as it dries to provide a subtle stain effect. Let the wash run down from areas where spills would occur like caps on fuel tanks. The flat dark red paint can be well thinned and allowed to flow down the sides of a weathered ship or submarine model to show rust stains.
Weathering a completed model kit using any combination of dry brushing and washes makes the model look much more realistic. The model becomes a scale replica of the kit subject by showing lifelike wear and tear.