IMPROVEMENT OF DC COLORING OF ANODIZED ALUMINUM WITH USE OF CERTAIN DIPHENYLMETHANE DERIVATIVES

deep bronze coloration is obtained during d-c treatment of aluminum sa mples, covered by a porous oxide layer, in acidic tin(II) sulfate solu tions containing the dyes Nile Blue, Methylene Blue, Pyronine B, and A cridine Orange in concentrations of 2.55, 1.39, 1.70, and 0.21 g/L, re spectively, The optimum conditions are 13 VDC and 3 min, The dye and m etal cations migrate to the cathode, to the insides of the pores, and are deposited at the bottoms of the pores, Reduction of hydrogen catio ns and dissolved oxygen occurs as well, which increase the local pH in the film, causing dissolution of the oxide to an extent dependent on the voltage and duration of tile cathodic treatment, These dyes, prese nt at the bottom of tile pores, by influencing these reactions, affect the extent of spalling or fine peeling of the film and increase its t in content and, consequently, the intensity of its color, The oxazine derivative, Nile Blue, added as the sulfate, yielded the best results.