Abstract: Anodized aluminum surfaces are electrolytically colored using alternating current in a process in which two different coloring baths are sequentially employed. One bath contains copper(II) ions and an additive which improves throwing power thereby providing uniform distribution of the depth of color. The other bath contains tin(II) ions, silver ions, or both tin(II) and silver ions. If tin(II) ions are included, additives which stabilize tin(II) ions and improve throwing power are also included. Either bath may be used first. The use of two separate coloring baths provides colored aluminum surfaces which have excellent resistance to corrosion. Workpieces with reddish-gold hues and darker tones can be produced.

Abstract: A manufactured stannous sulfate granulate is suitable for electrolytically coloring anodized aluminum with metallic salts, where the granulate particles have a linear extension from 0.1 to 10 mm. Also disclosed are a process for manufacturing the same and using it for electrolytically coloring anodized aluminum with metallic salts. The manufactured stannous sulfate granulate is characterized by technical advantages, such as storage stability, easy dispensibility, and absence of dust, compared to conventionally used stannous sulfate powders.

Abstract: The invention describes a novel electrolyte additive for a sulfuric acid tin(II) containing colorant bath for the alternating current coloring of anodized aluminum surfaces, consisting of a synergistic mixture of at least one antioxidant of one of the general formulas (I to IV) and at least one throwing power improver of general formula (V), and to a process for the alternating current coloration of anodized aluminum surfaces using the electrolyte additive of the invention.