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.
Cross-hatching is a rather rare drawing technique nowadays. However this is a well-known style due to works of such artists as Albrecht Dürer, Gustave Doré, John Tenniel, Rembrandt, Leonardo da Vinci. Igor Lukyanov is a Ukrainian artist who tries to follow the cross-hatching traditions of thos