Castings are used by engravers and engraving students as study pieces.  The casting is an affordable way to have a three dimensional representation of an engravers work.  They allow you to see his style and depth of cut, how he relieves background.  The elements you wish you could see in a photograph you can see in a good casting.

These castings are made by making a rubber mold off of actual engravings.  Then the mold is filled with liquid plastic that is allowed to harden.