Spit bite aquatint differs from the other aquatint techniques insofar as the printing plate is not put into acid. Instead, the acid is applied to the plate with a brush.
First a normal aquatint ground is applied to the plate, and then the artist paints on the plate with a thick acid solution. Traditionally, the acid was thickened with spit to make it more controllable when brushing it on the plate. The motif is thus etched on the plate in different tones, depending on the thickness of the applied acid.
Spit bite aquatint creates a visual effect similar to watercolour.