Mokume Care: Your ring has a glass bead matte finish. The finish will take on its own patina over time.
Precious metals are soft and will scratch from regular wear, which is normal.
Clean using mild dish soap and a very soft toothbrush. If the silver should become discolored (usually from pool chemicals), make a creamy paste of baking soda and water and rub over the surface with your fingers or a soft toothbrush.
Most often when a ring has dulled or darkened it is the sterling silver that has tarnished or oxidized. Normally with day-to-day wear the sterling silver will not oxidize. However water with high sulfur content or chemicals found in pools and hot tubs can cause the silver to oxidize. If a ring is left for a long period of time in a jewelry box or drawer it can also oxidize. As mentioned above it is usually easy to clean the ring and brighten it up.