When a string on a musical instrument loses its luster – that is, it’s there, but not all there – it’s said to have gone false. Strings can go false when their cores are wound wrong, or when they’re layered incorrectly, or when they’re stretched too far and then pushed back. If a string isn’t broken, but you wish it just would, it’s gone false.
Sometimes the oil on your hands makes strings produce black runoff. Washing your hands can help, as can the judicious application of cleaners and oils. The black runoff is inoffensive and harmless, but can still cause distress.
There are many common weak points for strings – namely, any point at which they touch the instrument. Strings can wear out at the nut, the bridge, or the tail end, all of which indicate that the body of the instrument is flawed; flawed in some miniscule and tender way that can wear strings away slowly or snap them in a moment.
Those first strings were made of gut, real gut, and this material is still used. New Zealand sheep gut is especially highly prized. Something about their diet and the altitude. Talk about terroir.
But sometimes gut is too real to be stable. It can just keep on stretching when you put pressure on it, which is really no good at all. Synthetic cores are really quite a lot more stable, which is why they have become favored by many manufacturers and players.