Chasing metal is defined as The techniques of repoussé and chasing use the plasticity of metal, forming shapes by degrees. There is no loss of metal in the process as it is stretched locally and the surface remains continuous. The process is relatively slow but a maximum of form is achieved, with one continuous surface of sheet metal of essentially the same thickness. Direct contact of the tools used is usually visible in the result, a condition not always apparent in other techniques, where all evidence of the working method is eliminated.
This photo is an elephant from Nepal in 1640. Thank You Rubin Museum! http://rubinmuseum.org/
Pretty cool place to visit if you are in NYC.