Chill out Dubster. You are spot on about pin washes but for a sludge wash you can indeed apply with an airbrush. When using the Flory washes I have not airbrushed but have applied it all over with a wide brush. When it is dry you moisten a cloth and work over the model wiping in the direction of airflow or gravity removing the wash, getting it into the nooks and crannies where you want it to get the effect you want. It can work very well and most of my models have when done that way. There are different ways of dong the job with different materials.