Clasps can be adjusted for personal preference. A harder louder "click" will mean that the clasp is less likely to come undone, but may be harder to take on and off. Earrings come with a medium hard click.
To adjust tighter squeeze "U" between fingers gently and check click with ear wire. To open wider use fingernail to gently pry open and check click with ear wire. Through daily use you may notice the click becoming softer again. If this happens just re tighten using the above technique.
Bronze reacts with moisture and oxygen and will naturally darken or patina over time. You can lessen this effect by storing preventing your earrings from becoming wet and storing them in a dry place. If you would like to remove the patina a green kitchen scrubby and toothpaste will remove the patina quickly and easily and return your piece to a bright shine.