2 step coloring

2 step coloring process has been industrialized in the early 1960s and this is the way of coloring by electrochemically precipitating the metals into the micro-hole (150 - 200Å) of the anodic oxide film.

[Fig.1] Model diagram of 2 step coloring condition

Fine particles of nickel precipitated into the pores of sulfuric acid film

Nickel was precipitated into the oxide film by Asada method under the following conditions; Sulfuric acid:180g/l, current density:1.5A/d㎡, temperature:20℃, time:40min
  • Picture magnification:x 320,000
    (Literature) L.Sandera. Aluminium 49,533(1973)
    (Offered by) L.Sandera(Swiss Aluminium Ltd.)
    (Introduced by) Nobuyoshi Baba(Tokyo Metropolitan University)

  • Cross-section of the film electro-colored by nickel salt, after normal sulfuric acid film of 99.8% Al was intermediately processed in sulfuric acid bath for 15 minutes.(Offered by Kenji Wada of National Institute for Research in Inorganic Materials)

[Chart-1] Typical 2 step coloring process

Summary Typical method Color tone
Anodic oxide film is electrolyzed by DC or AC in electrolysis bath containing metallic salts like Ni, Sn, Mn, etc. At NACL, there are various methods such as
① H color, ② NK gray, ③ KN color.
Stainless, Amber, Bronze, Black, Gray, etc.
Process outline

Process outline:Process of anodizing

Process outline:Process of complex film

Process outline:Process of painting

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