This polishing cake is actually a small block of emery impregnated rubber. It works a lot like a pencil eraser. It works miracles in removing tarnish and dirt from steel, brass, phosphor bronze plain or wound musical instrument strings. In some cases we've been able to restore old strings to near-new condition by simply polishing with this cake, and thereby avoiding the need to completely restring a hammered dulcimer (which, by the way, is quite a job!)
Every hammered dulcimer player should have one of these polishing cakes in his or her case. It can keep your strings "like new."