What does Jack do to himself that turns him into an "awesome stranger"?

He paints his face;

Jack planned his new face. He made one cheek and one eye-socket white, then he rubbed red over the other half of his face and slashed a black bar of charcoal across from right ear to left jaw […]. “Samneric. Get me a coconut. An empty one.”

He knelt, holding the shell of water […]. He looked in astonishment, no longer at himself but at an awesome stranger. He split the water and leapt to his feet, laughing excitedly. Beside the pool his sinewy body held up a mask that drew their eyes and appalled them. (4.31-33)