From googling...
In 1895 William J. Sager, then of Warren, Pennsylvania, was issued a patent for a chemical treatment that was intended to reduce oxidation and prolong the finish of the metal that it was applied to. The process was actually a two part procedure. The first involved dipping the metal to be forged into a chemical mixture and then hammering the metal. That was done when the metal was very hot. The second stage was part of the quenching process implemented when the metal was heated to a red hot color after being tempered. The chemical solution was actually the quenching solution. The end result was a metal tool with a deep lustrous blue coloring that was claimed to be a higher quality and more durable than metal not treated in a similar fashion. The blue coloring itself was protected by a coating of clear finish.
