This original print is a very deeply etched zinc plate, bathed in acid for roughly 8-12 hours for some parts of the plate.  Printing is done in one pass through the press.  

Three colors are applied by wiping the first color in the usual intaglio manner with red.  The second color is a very oily yellow and is applied with a hard roller, so that the roller only places ink on the high surface of the plate.  The final color, a dry or tacky green ink, is applied with a very soft roller that sinks deep into the plate.  The dry green ink skips over the oily yellow, and sticks to the plate only where there is not already an oily film of ink present. The technique is called viscosity printing because the outcome of the placement of the ink on the plate depends on the relative oiliness (or viscosity) of the 3 inks.