Abstract: A process for the electrolytic coloring of aluminum or aluminum alloys consisting of subjecting the previously anodized piece to two electrolytic treatments in a coloring solution (solution of soluble metal salts). The first consists of an alternating current treatment with an elevated positive polarization, to cause a modification in the pores of the anodic layer. After this electrolytic treatment and in the same bath, the sample is colored by applying thereto an alternating current. The electrolytic treatment prior to coloring permits colors differing from those produced in conventional coloring to be obtained.

Abstract: The present invention provides an improvement in the process for electrolytically coloring aluminum or an alloy thereof comprising the sequential steps of anodizing, coloring and fixing. In accordance with the improvement, the coloring step is conducted under conditions wherein the ratio between the concentration of the sulphuric acid used and the concentration of the color-producing salt or salts used is from 70:1 to 15:1, the concentration of the sulphuric acid being about 15 g/l and the salts used being metal sulphates, and wherein the peak voltage applied is from 10 to 45 volts and the temperature is about 25.degree. C. and wherein at the beginning of the coloring step of the process, the voltage is increased from 0 up to the peak voltage in a progressive and controlled manner.

Abstract: A system for generating and autocontrolling the voltage or current wave form in a process for the electrolytic coloring of anodized aluminium includes feeding power from a source of symmetrical direct current, with a neutral connection directly coupled to a load, while the positive and negative voltages supplied by the source pass through a power control stage which is controlled by a bipolar operational amplifier. The bipolar operational amplifier has two signal inputs, a positive or non-inverting input which is connected to a signal generator, and a negative or inverting input having a signal which corresponds to the signal which actually exists on the electrodes of the electrolytic bath. This signal is processed in a half-wave outer controller which is controlled by a programming system.

Abstract: Apparatus for electrolytically coloring anodized aluminum comprises a power transformer whose secondary winding has one phase connected directly to the charge and its other phase connected to the charge through two anti-parallel thyristors. One of the thyristors is triggered in accordance with a predetermined program, and the other thyristor is triggered in dependence upon unbalance in the average values of the voltages applied to the charge in consecutive half cycles of the alternating current applied to the charge, in such a manner as to tend to eliminate the unbalance.