Pencil on paper. This is a self-portrait as a postage stamp, at the actual size of a postage stamp, drawn on an actual envelope.

I used a mechanical pencil for this, as I do for almost all my pencil drawings. When I draw with mechanical pencil, I alternate drawing with scribbling at an angle on a piece of scrap paper, to wear down the lead in a specific pattern. One side of the lead becomes a wide flat surface, suitable for shading. The other side becomes a very fine point. This fine point was what I used to make the tiny, precise lines of this drawing.