The present invention relates to solutions used to polish jewelry and in particular an aqueous solution for the electrolytic polishing of articles made of precious metals.

The polishing of metal articles is usually carried out according to various methods, such as mechanical polishing by means of abrasive implements such as grinding wheels, brushes, etc., treatment by means of suitable solvent liquids, electrolytic finishing through the action of electric current on the articles used as electrodes immersed in suitable solutions.

The polishing usually carried out in goldsmith's workshops is an electrolytic polishing of jewels immersed in a solution containing essentially cyanide ions deriving from compounds such as cyanides and ferrocyanides of alkali metals, by the use of suitable equipment.

As the utmost toxicity of cyanogen and its derivatives is well known, the competent authorities have enforced strict prohibitions to the use of said cyanic compounds, which made illegal the conventional methods of galvanic or electrolytic polishing with cyanides. The present invention aims therefore at providing a novel solution for polishing jewels, which is free of the above named drawbacks.

The solution according to the present invention is basically formed by one or more organic compounds containing ionizable hydrogen and comprised in the group formed by thiourea, cysteine, methionine, alanine, glycine and their derivatives, mixed with sulfamic acid and a sulfamate dissolved in water; the polishing process carried out by such a solution is an anodic process wherein the jewel is used as the anode, and the polishing effect is obtained by removing little amounts of metal from the surface of the treated article. A particularly preferred solution comprises thiourea or cysteine, copper sulfamate and sulfamic acid dissolved in water or other aqueous vehicle in variable proportions according to the operating conditions, such as voltage, intensity, kind of electric current (direct, pulsating, etc.), bath temperature, treatment time, and so on. The following examples, simply given for explanatory but not limiting purposes, will better explain the object of the present invention.

EXAMPLE 1

A red gold jewel connected to the anode of a direct current source so as to have a current density of 1 A/cm ² is immersed in an aqueous solution containing 80 g/L of cysteine, 100 g/L of sulfamic acid and 100 g/L of copper sulfamate, with pH about 2, and is treated under voltage at a temperature of 80°C up to the attainment of the desired brilliance.

A totally similar effect can be obtained by substituting for cysteine a corresponding amount of thiourea, as it is clear from the following example. EXAMPLE 2

A red gold jewel connected to the anode of a direct current source is immersed in an aqueous solution containing 50 g/L of thiourea, 60 g/L of sulfamic acid and 5 g/L of copper sulfamate, with pH about 1 , and is treated under a variable voltage of 16 V to 28 V according to its weighing into carats at a temperature of 80 °C up to the attainment of the desired brilliance.

Although the present invention has been described and explained by means of preferred embodying examples, it is evident that given changes can be made without departing from its gist and leaving its protective scope.