Soft ground is a hard etching ground to which fat has been added to make it soft and sticky. This makes it possible to make an imprint in the ground itself, by pressing an object or texture into the ground.
If, for example, you press a leaf into the ground its fine structure will pull away the ground when lifted from the plate, exposing the copper below, allowing the acid to etch a very detailed impression of the leaf into the plate. The same principle applies when drawing on a piece of paper placed on top of the soft ground. The pressure of the pencil will push the paper into the ground, and when the paper is removed from the plate surface, small points of the soft ground will stick to the grain of the paper. The copper is exposed wherever a line was drawn on the paper. When the plate is exposed to acid, it will bite only the uncovered copper, forming an image of grainy lines. The plate is filled with ink and the surface wiped clean before it is run through the press. When printed the lines look like pencil or crayon lines.