The Blue Passion-flower, 1799-1807. In the 18th century, new engraving and etching techniques offered a variety of tonal effects that enhanced botanical prints. While mezzotint (in which the plate is roughened and then the engraver works from dark to light creating different values) and stipple (dots create values) make it possible to create the rich tonal scale and velvety texture of oil paint, aquatint imitates the delicacy and transparency of watercolour and ink wash.