In his Divine Comedy, Dante describes the pilgrimage he made with the poet Virgil, travelling into Hell, up the Mountain of Purgatory to reach Paradise at last. Entering the Gate of Hell was a moment when Dante (in red) wept with fear.
Dante describes the ‘dim’ colours which contribute to his terror. Blake’s dark shadows of pure black pigment next to areas of unpainted white paper contribute to this. He used Prussian blue for the blue areas, and indigo blue mixed with yellow for the green foliage, so that they contrast. The blue, green and vermilion red do not overlap.