What is that? A piece of chocolate?
It's a rust eraser!
Check This Out … Officially, Polita Steel Polish. Description from Elderly Instruments : "Rubber / steel compound that resembles an eraser. Often used by dulcimer players to clean strings."
Indeed. And from the good folks at Song of the Wood : This polishing cake is actually a small block of emery impregnated rubber… 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, thereby avoiding the need to completely restring a hammered dulcimer … which, by the way, is quite a job!
Only $10. Just in time for spring cleaning!