Improving a procedure for determining the assay of gold in a precious alloy of different composition using a touchstone

Abstract

We report testing the and jewelry alloys based on that contains nickel, zinc, palladium, using a touchstone by applying various chemical reagents and XFA (X-ray fluorescence analysis).We have improved the procedure for assessing the conformity of assay of the precious alloys based on considering the content of component composition by using the results from rubbing the alloys on a touchstone.It was established that the magnitude of assay for precious alloys in the system AuAgZnCu, determined under the action of the reagent chloric gold on the touchstone, depends on the manifestation of contrast in the course of quality reaction against a standard sample (touch-needle).Under the influence of the reagent, the alloys demonstrate chloride compounds with silver and copper, being reduced to a metal powder of black and brown color. In this case, copper dissolves while together with silver, forms an intensive residue on a strip that depends on the ligature composition of the alloy. It was established that the lower the assay of a tested sample, the greater the amount of chlorine gold that decomposes, the larger the sediment of silver chloride and the pure reduced from the reagent, and hence the darker the sediment.It has been proven that testing the precious alloys of red color from the system AuAgZnCu 585 with a content of zinc (over 2 %), nickel, indium by using a reagent based on potassium dichromate and copper chloride is not effective.The results of our analysis indicate the increased assay compared with a standard touch-needle.To eliminate this phenomenon, it is recommended that one should first determine the composition of an alloy by the XFA method and construct an algorithm for testing in accordance with the content of the alloy by other reagents.It was determined that the assay defined on a touchstone for alloys from the system AuAgZnCu 585 (a content of zinc is over 2 %) is more contrast under the influence of acidic reagents and depends on the component composition of the alloy.It has been proven that the alloy of white gold, composed of palladium and silver (AuAgPd585), is not affected by the acid reagent for assay 585.Testing the alloy of white gold (AuAgPd585) using an acid reagent for assay 750 yields the dark sediment of a bluish tint.We have established a more contrast effect on the alloys of white gold and yellow gold of assay 750 from the acid reagent for alloys of assay 750.