Freehand scroll/portrait on a black vehicle

 

Undercoat Heavy Brown, then basecoat Wraithbone.

Trace the scroll Khaki. Trace the face and writing Nuln Oil. This is a rough sketch to see how much space the drawings take up. Erase by painting over Wraithbone as many times as necessary.

Once final, stiple Agrax Earthshade unto the scrollwork.

For the scroll, simulate highlights on a curved surface using Bonewhite and Wraithbone.

Trace the writing and the portrait Basilicanum Grey.

Trace the outline of the scroll Cygor Brown.

Finally apply any weathering to the surrounding surface. Make sure to chip into the scrollwork, but don't obscure any important details.