When hammering the copper sheet, let the weight of the hammer do the work. Also, if your backing material has a texture, hammering on it will emboss that texture on the copper sheet. One of the more interesting looks can be achieved by hammering the copper sheet on concrete. An important word about safety, always wear eye protection when you are hammering copper sheet and gloves do help when handling the sharp edges of the copper sheet metal.
This red colored metal has been in use for many years, humanity has found 
copper and started using it already in Greek ancient times, this use of copper and other metals has evolved since ancient times, and as is the case in copper it has been used for more technological advanced things than the production of mirrors. The use of copper has been so wide over the last few years that many have started stealing copper, in any form, to sell afterwards. Just one last word about copper, you probably realized half way through reading this that copper does have a very significant role in our lives, from our kitchens with their copper frying pans, pots, knives and forks, to coins and change made part of copper, pipes and awnings and many more products that we have become almost blind to, have copper in them.