The washes are always needed to blend the edges of the colors on a model painted in various camouflage shades. The colors can also be mixed together to achieve further variations of shade and can be used with airbrush or brush, according to the model and the effect desired.
Wash can be mixed with pigments to achieve a wide range of effects such as oil and flaked rust, mud, earth, dust, moss, etc. and when mixed with acrylic colors, they further help achieve the impact of heavy wear and weathering.