When environment is forced into a furance burning away impurities. It creates pig-iron more pure. It's the old approach to steal manufacturing.
a commercial process to make metal making use of a Bessemer converter to blast atmosphere through molten metal and so burning the excess carbon and impurities; the very first successful method of making metallic in quantity at inexpensive
The first period began in extremely remote prehistoric times; the second in the 14th century; and the third with the invention of the Bessemer process in 1856.