Ink.
"I became enamored with pen-and-ink early on in my art career, eventually seeing it as a way to capture spontaneous weirdness of my sketchbook drawings. Initially drawing upon my experience in archaeological illustration, I soon discovered in pen-and-ink a way to capture an intense detail within a larger whole. I mainly use a dip pen and non-waterproof ink. I don't use literal dots to shade--more like micro-stroke or slashes, which allows me to give movement and energy to the piece. I have also done forays into ink-wash, and colored-ink mixes."
Pen-and-ink, brush-and-ink, colored ink, etc.