Concerning impurities in gold alloys, it is well known how detrimental the influence of some elements can be, but few know that at certain concentrations they can act positively on the properties of the product.

This talk will discuss the influence of certain elements, discerning between metallic impurities such as lead and non-metallic impurities such as sulfur, and trace back their origin as well as their influence, be it positive or negative. Sometimes it is not the element that is critical, but rather its concentration. Silicon and aluminum at low concentrations act as deoxidizers but embrittle the material at higher concentrations. Iridium can act as a grain refiner but at higher concentrations it forms inclusions. Lead is a very critical element. Its influence not only originates from its concentration but also is affected by heat treatment of the alloy. At rather low concentrations it acts as a strong recrystallization preventing addition.

Certainly non-metallic impurities such as oxides and sulfides are of importance too, especially since their effect is different in silver, gold, and platinum alloys. Of very great importance are grain refining additions which up to now, in the author’s opinion, are used too little. This lecture will cite the most important impurities for jewelry manufacturing, their origin, their detection and their elimination.

Author: Christoph Raub