Principle of electrolytic coloring

Electrolytic coloring is the reduction of metal ions on the barrier layer at the bottom of the membrane pores to develop color. However, the barrier layer of aluminum is not chemically active. To electrodeposit metal on the barrier layer, the key is to activate the barrier layer. Electrolytic coloring uses sine wave alternating current, which is to use the polarity change of alternating current to activate the barrier layer. The barrier layer is damaged in the negative half cycle and oxidized and repaired in the positive half cycle, so that the barrier layer is activated. Therefore, electrolytic coloring must use alternating current. So how can the alternating current reduce the metal? This is because the barrier layer has semiconductor characteristics and can play a rectifying effect. When the potential of the opposite electrode is higher (positive) than that of the aluminum part, the negative component of the current on the side of the aluminum part is dominant. The metal ions diffused into the pores of the membrane are reduced and precipitated by the reduction of the cathode. Studies have shown that precious metals, copper and iron group metal ions are reduced to metal colloidal particles, and some oxygen-containing acid radicals such as selenate, molybdate, and permanganate are reduced to metal oxides or metal compounds to precipitate and deposit on the membrane wall.

The color tone of electrolytic coloring varies according to the type of metal salt and the amount of metal deposition. In addition to the characteristic color of the metal, it is also related to the size, shape and particle size distribution of the metal colloidal particles. If the colloidal particle size is in the visible light wavelength range, the colloidal particles are Light waves are selectively absorbed and diffused, so that different tones can be seen.