The Name
The Latin term intaligo which means incise applies to the printing techniques which result in the
image being created below the surface of the plate. The material used for forming plates up to
the early 19th century was copper sheet, this diminished after the the invention of the
more economic mild steel. So to engrave literally means to incise furrows or grooves on a
copper or steel plate with the use of a graver or burin.

The Technique
The engraver worked with the lozenge shaped tool called a graver or burin,
rotating the plate as he worked. The lines were incised into the plate with varying widths
and depths by altering the angle at which the tool met the plate and the amount
of pressure exerted on the handle. Differing tones were achieved by changing the
space between the lines, closer together gave a darker area. Cross hatching also
produced tonal and textural effects as well as providing a more three dimensional image.
See an example here.

See also Etchings Lithography and Chromolithography