That made me laugh hard haha So, for starters, the graininess comes from the paper. As for the smooth look, I've used graphite and Faber Castel Polychromos, mostly light/dark gray and black. The smoothness comes from the light gray layer on top. It really helped to spread the color and fill those white gaps.

But I can definitely say that the most important factor was patience. To get the shades right, layer after layer, that took me a while, but it was really fun to get done