Etching is a general word meaning that acid was used to incise the plate. In making an etching, the plate is first coated with an acid-resistant material called a ground. The names of the various types of etchings come from the types of grounds used. Hard ground and soft ground are used to make lines, and an aquatint ground is used for tones. Grounds for line drawing are usually made of wax.
In hard ground etching the artist draws through a hard wax that coats the plate. Hard ground lines are usually thin, wiry, and blunt at the ends. You can see this type of line in Wayne Thiebaud's EIGHT DOGS, shown here.
In soft ground etching the lines look like pencil or crayon lines, and are made by drawing on a piece of paper that covers a soft wax coating on the plate. When the paper is lifted off, it removes the wax where the pencil pressed, but some wax stays in the lines in the pattern of the paper grain. The picture shows Richard Diebenkorn drawing with a pencil on a piece of paper over a plate coated with soft ground.
His print, RED, YELLOW, BLUE shows the kind of lines made by this technique. In the etchings of contemporary artists, you will probably see more soft ground lines than any other kind. Soft ground also can be used to create faithful images of fingerprints, leaves, lace, or anything else that can be pressed into soft wax.
The lace in Robert Hudson's soft ground etching GREEN AND RED RHYME is an example.