Why and how does this happen? Three main reasons:
- Rubbing, knocking, or pressing against things (obvious things like walls, doors, etc., but also other jewelry, clothing, bike handlebars, dumbbell bars, even bedsheets… basically anything you hold or brush up against)
- Exposure to natural elements like the air, moisture, skin/sweat/body chemistry. Read more about tarnish.
- Exposure to other chemicals from bath/body products, pools/hot-tubs, even off-gassing in manufactured products.