On the last few models I have airbrushed and then weathered I have used some artist silver pencil. I did try normal HB but it is a little dull and not as bright for the very fine edges.
I know that many in the military scale modelling hobby use them on tank tracks as a final road scuffed edge. They are great on rusty areas where you might want to show the smallest amount of naked metal along the edge. On this GZG 15mm sci-fi mobile artillery vehicle I have used it along the edge of the barrel and on the tracks.
You do have to be careful with your spray matt final coat because it can dissolve the pencil lines. You could either add it after the protective matt varnish or simply go easy with the dull layer. I found if I rub hard on the fine edges it does stick on enough to last through the varnish spray but it does dull it a little.