Before revision: The Platinum-Cobalt Scale (Pt/Co scale or Apha-Hazen Scale ) is a color scale that was introduced in 1892 by chemist Allen Hazen (1869–1930).
After revision: The Platinum-Cobalt Scale (Pt/Co scale or Apha-Hazen Scale ) is a colour scale that was introduced in 1892 by chemist Allen Hazen (1869–1930).