While 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 utilize 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. This is from the Wikipedia definition of Repousse or Tin Tooling.
Historically craftsmen used the art form to produce a variety of decorative functional pieces from serving dishes to jewelry and is still produced by a number of talented craftspeople around the world. We can use the techniques that were employed on a smaller scale to add interesting detail to cards, mixed media pieces, and decorative pieces of art work. Your goal in the process is to stretch your tin so that you achieve the raised edges on the front (emboss) making sure that you work on a soft surface which will allow that tin to stretch. You can use a magazine, pile of newspapers, piece of foam or anything that will allow your tin the ability to be elastic. It isn’t necessary to invest in tools to be able to tin tool, you will need a stylus and tin that is soft enough to be able to emboss. We use a stylus to transfer the design; the stylus can be either metal or plastic depending on your preference, making sure to always work on a soft surface. The stylus is held upright at a 90 degree angle which will allow the full impact of the point to achieve that deep ridge while you apply pressure to the stylus.
Tooling tin comes in a variety of thicknesses (gauge) and depending on what you want to do with it will determine the thickness that you want to use. I generally use a 32-40 gauge tin and find that is a good thickness for either 3-dimensional projects or flat projects, the higher the number the softer the metal. This thickness of tin can easily be cut using a pair of scissors or a paper cutter. There are a number of tools that you can purchase including a variety of texture tools which accomplish a number of different textures including wheeled tools or texture plates. Many household items will also give you an interesting texture on your tin, use your imagination, I often use my Cuttlebug plates to achieve interesting textures and if your tin is soft enough can run the tin through your embossing and die cutting machines. You just need to experiment with this.