Before germanium became the miracle anti-tarnish ingredient in silver, a small group of refiners discovered that platinum-group metals could whiten and brighten sterling as well as shield it from fire stain. Today, there are at least half a dozen silver alloys that rely on platinum and palladium to keep tarnish and fire stain at bay. While these alternative alloys are all more ­expensive than germanium-based ones, they are considerably less costly than their white gold counterparts. Moreover, they allow jewelers to sell sterling jewelry that owes its beauty and durability to its ­precious metal content.As you would expect in a cost-conscious industry, there are fewer users of platinum-group sterling alloys than germanium-based ones. One of this still-small band is Victor Joyner of ­Chicago-based HD Pattern Co., a firm that specializes in new casting technologies using polymers. Last y