Pin Washes

Good question there, 'Fox.

A "pin" (or pinpoint) wash is simply a localised wash applied to specific details, such as bolt heads, crevices, panels lines etc., applied with a fine-point brush, as opposed to a conventional wash which is applied to a wide area using a broader brush.

So it's like doing panel lines on a plane with a fine tip brush?

It's similar.

Mix your wash very thin - eg. 90-95% thinner, and touch the tip of your brush to the part you want to highlight. Capillary action will draw the thin mix around the part (eg. bolt heads) or along corners and panel lines.