COLOR TONE AND CHROMATICITY IN A COLORED FILM ON STAINLESS-STEEL BY ALTERNATING-CURRENT ELECTROLYSIS METHOD

A coloured film was formed on SUS 304 stainless steel in an aqueous so lution containing 2.5 M CrO3 and 5.0 M H2SO4 by the alternating curren t electrolysis method. Quantitative measurement of the colour tone and colour difference were conducted to evaluate the controllability and reproducibility of the colouring process. The chromaticity of a colour ed film formed at 80 degrees C appeared much higher in degree than tha t of films formed at 72 and 65 degrees C. A cathodic peak potential, E (cp), as measured on specimens increased with the colouring time. A di fferent colour tone of the coloured film was obtained at specific E(cp ) used during the colouring process. E(cp) values around 420, 750, 850 and 950 mV displayed colour tones of blue, blue-golden, golden and pu rple respectively at 80 degrees C. A desired colour tone of the films was achieved by measuring the E(cp) or by controlling the alternating current cycles (N). Either method exhibited an excellent reproducibili ty, with the colour difference (Delta Eab) within 0.9. Although the v alues of E(cp) and N were dependent on the colouring temperature, adju stment of the colour tone was available through use of either E(cp)-co ntrolled or N-controlled methods to overcome the problem of temperatur e drift, and thus a constant colour tone was assured.