An Aquatint is an erosion process. Parts of the copper not covered by a stop solution (in the form of lacquer, shellac, or varnish) are eaten away by acid. In an aquatint the copper plate is covered with a powdered resin, then heated in order to form a bond between copper plate and resin. A stop solution is applied to make some areas remain white. The areas covered by the resin will leave Varying degrees of gray, depending on the thickness of the resin powder on the plate. The cracks between the resin will be eroded or etched by acid. Thus the etched cracks will hold most of the ink and will print black.
Clark had a profound interest in heritage. His son Claude Lockhart would one day pursue the same interest at a very early age.