I have discovered a safe and clever way to create washes on figures. You will need any type of normal airbrush specific paint and airbrush paint wet-or-dry solvent (for cleaning air brushes). First, take a brush and brush airbrush paint into and around the areas where you want your wash to go. The result, at the current stage, is filled recesses but the rest looks like it has been dropped in oil. Second, you pour a small amout of the solvent onto a paper towel. Make sure the solvent isn't dripping off the paper towel or else it will flow into the low areas on your model and remove the airbrush paint. Wipe the paper towel with the solvent over the model. This rids the model of excess paint on the raised surfaces and leaves a very nice wash. The ability of the solvent to remove paint even when it has dried allows you to apply the airbrush paint and leave it be for however long you want.
Make sure the solvent desolves the paint you are using.