The extraction and refining of nickel from its ores. Nickel's properties of strength, toughness, and resistance to corrosion have been used to advantage in alloys since ancient times. Paktong, similar to modern nickel silver, was used in the sixteenth century in China, and early weapons were often fashioned from tough, nickel-bearing meteoric iron. A. F. Cronstedt first isolated nickel as an element in 1751, and in 1804 H. T. Richter prepared it in relatively pure form.