several hatchings such as cross lines and dots are used to represent the depth within this portrait. as seen in this image the darkness of an area is shown by doing a much more of a closer/tight hatchings.
today's convo: "Respect yourself enough to walk away from anything that no longer serves you, grows you, or makes you happy." -Robert Tew "I’m used to it." -Anonymous, (the saddest thing you can hear someone say) artwork by Noel Badges Pugh