A wash is basicly a thin paint. Pigment by itself can be applied to get a similar effect. Washes can also be applied as a pin wash, to nestle into panel lines without staining the surrounding surface, which is difficult with dry pigments.
Both produce a semi-transparent affect, like a stain. If you are very good with an airbrush you can get the same effect with it. So there are at least three methods of replicating stains- probably more. Dot filters do pretty much the same thing.