A long established and universally used technique (often called embossing) of producing relief decoration on a metal plate by punching and hammering thin metal from the reverse in order to raise the design on the front. The metal plate is sometimes turned over so that some embossing can be done on the front to enhance the desired relief design.
The work is done by means of hand punches and hammers, or sometimes by mechanical means by the use of metal or stone dies (called 'embossing dies'). The metal to be decorated is laid on a bed of a yielding material (e.g. wood, lead, leather sand-filled bag, or usually pitch) after the design has been scratched on with a tracer, and then the design is punched and hammered in, with periodic annealing to prevent the metal from becoming brittle.
On some examples the relief design is refined by chasing on the front (sometimes called 'repoussé chasing') or engraving, or sometimes embellished by additional metal soldered to the front. Sometimes, in imitation of true repoussé work, the decorative design is not beaten from the reverse but pieces of metal are cut out separately, embossed, and affixed to the front. The process must be distinguished from stamping.
From: An Illustrated Dictionary of Jewelry, autor: Harold Newman, publishers: Thames and Hudson
Repoussé or repoussage is a metalworking technique in which a malleable metal is ornamented or shaped by hammering from the reverse side. There are few techniques that offer such diversity of expression while still being relatively economical.
Chasing is the opposite technique to repoussé, and the two are used in conjunction to create a finished piece.
Whilst repoussé is used to work on the reverse of the metal to form a raised design on the front, chasing is used to refine the design on the front of the work by sinking the metal. The term chasing is derived from the noun "chase", which refers to a groove, furrow, channel or indentation. The adjectival form is "chased work". The techniques of repoussé and chasing utilise the plasticity quality 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.