A water-based, non-toxic acrylic miniature wash manufactured by Games Workshop.
It is specifically formulated to run into the recesses of Warhammer and other tabletop miniatures to create realistic depth, shading, and natural-looking shadows with minimal effort.
Apply Casandora Yellow directly over a lighter base coat (such as a white, off-white, or yellow base) using a shading brush. The paint washes over flat surfaces and pools heavily in the crevices to define details automatically. 
If too much pool forms on flat areas, simply wick the excess away using a clean, damp brush before it dries.