The carborundum technique is not really an etching technique because the plate is charged with material instead of engraved.
A grain is applied on the plate with a varnish or glue (the design). The plate should be sufficiently solid to receive the pressure of the press and to allow the cleaning after the print but is not necessarily a metal plate (plastic, certain cardboards, etc. can do the job).
The glue can be a varnish, epoxy or other rosin based product that can be applied with a brush.
