Sometimes you just have to do a quickie. This is a small (8″ x 10″) scratchboard of a zebra from one of my Africa trips. Simple process, do the drawing, remove all of the ink from the white stripes with a fibreglass brush so you are back to pure black and white, then use an airbrush (or use a large watercolour brush) to add a layer of diluted Indian ink over the whole thing, wait til it dries and use the fibreglass brush again to pull out some highlights. Repeat the ‘pushing and pulling’ process of airbrush and highlights until you have the desired 3D roundness you need to make the zebra look like you want it to look.
My photo of it has caught some glare here and there unfortunately but you get the idea.