Proof Sets have been marketed by the mint since 1936. Proof coins go back at least to the early 1800’s and collectors could go to the mint prior to 1936 and purchase proof coins or sets. These earlier Proof Sets are extremely rare.
Proof coins are made by using highly polished dies and giving two or more blows to the coinage blank or “planchet”. The result is a very sharply struck coin with highly reflective or “mirrored” surfaces.