Nickel-free Sterling Silver Alloy Compositions and Method of Preparation

Abstract

A new nickel-free sterling silver alloy with superior tarnish resistant, yet substantially similar cold working and mechanical properties is disclosed using a specified mixture of zinc, copper, silicon, iridium, and indium with pure silver. A new and improved method of manufacture involving a four-step process whereby the non-silver components are fabricated in an inert gas or reducing atmosphere into a master alloy of pre-determined composition, and in a final step mixed with a predetermined mass of pure silver to produce the new alloy.

1 . A new and improved nickel-free silver alloy with exceptional tarnish resistant qualities, said alloy is essentially comprised of the following elements by percent (w/w): 
       
         
           
                 
                 
                 
               
                     
                     
                 
                     
                   Silver (Ag): 
                   about 92.500% 
                 
                     
                   Zinc (Zn): 
                   about 1.000% 
                 
                     
                   Copper (Cu): 
                   about 6.315% 
                 
                     
                   Silicon (Si): 
                   about 0.100% 
                 
                     
                   Iridium (Ir): 
                   about 0.025% 
                 
                     
                   Indium (In): 
                   about 0.060% 
                 
                     
                     
                 
             
                
               
               
                
                
                
                
                
                
                
               
            
           
         
         whereby said new alloy exhibits significant improved resistance to tarnishing. 
       
     
     
         2 . A new and improved method for the manufacture of a highly tarnish resistant sterling silver alloy as described in  claim 1 , comprising the steps of:
 a first step of manufacturing a master alloy by melting a predetermined amount of copper in a crucible;   adding predetermined amounts of iridium and mixing;   reducing the mixture temperature to a few degrees above the freezing point;   adding a predetermined amount of indium and further mixing;   maintaining a reducing atmosphere over the crucible;   cooling the master alloy and forming either a bar or dispersing the master alloy into water to form granular pieces;   drying the master alloy;   melting a predetermined amount of pure silver into a second crucible;   adding a predetermined amount of the master alloy to the second crucible;   mixing the molten silver and master alloy forming a new sterling silver alloy; and   cooling the new sterling silver alloy and forming either a bar or dispersing the master alloy into water to form granular pieces.