|A dusty M1-Abrams. Photo courtesy of Defense Link.|
Dust is the is the main agent in an AFV looking dirty. It can be simulated by three methods; each depicting slightly different accumulations of dust. Use them in combinations for the following effects:
Old Heavy Dust: Using successively built up layers of thinned earth coloured paint. I prefer Tamiya Flat Buff and Flat Earth with some white tube water paint, mixed with water and a drop on Windex as a wetting agent. brush this mixture on, letting it collect around rivets and in crevices. This is the exact opposite to the "standard" drybrushing method of accentuating raised detail with lighter coloured paint. However, it is far more realistic - when dust is blown or rubbed off an AFV it tends to stay around rivets and in crevices and not on raised surfaces. Use a hairdryer to dry the model off fast - but be very careful not to melt the model.
New heavy Dust: Spray the above mixture with an airbrush. For a thicker application, thin the paint less. It is important to refer to reference photographs and to works slowly as it is easy to end up with a model that looks as if it has been sprayed with earth coloured paint and not road dust!
Light Dust: Pastel chalks, ground up and applied with a large (round no. 6) red sable brush. The final coat should be blown on. Always apply chalk dust except for AFV in winter, jungle and other extreme wet conditions. To simulate a recent, light rainfall spray the dusty model with water from a mister bottle - the effect is quite stunning.
Chalk Brands: Its worth noting what pastel chalks are. They are not the standard black-board chalks but artist's quality coloured drawing chalks. Get several earth colours. They will last for literally years of intensive weathering.
Fixing With Clear Coats: This is not recommended. Applying any clear top coat, whether it be enamel or water base will ruin the subtle effect created by the chalks. Also the colour will be darkened. The only way to avoid fingerprints is to either fix the model to a base or handle the model with extreme care. If finger prints do get on the model, however, they can be easily brushed out with a little more chalk.
Oil And Fuel Stains
These are best replicated with washes. Its debatable as to what colour petrol, if any, should be. However, a slight green tinge to the wash looks pretty good. The trick to a good gas stain, however, is not to colour the model, but to affect the previous weathering. Therefore gas and oil stains should be the last effect applied. Oil of course should be a medium wash of dark brown-black. The wash will stain any chalk dust and end up looking just like the real thing. For older stains, reapply chalk dust just before the wash dries, but don't use a brush as it will leave streaks, just blow it on. The dust will collect on the wet wash and when dry look most realistic.
While none of these techniques are ground breakingly new, I think the philosophy of effect over technique is - keep this in mind when you weather your next model. And have fun!