Your napkin rings are very solid and will last over time, but they require special maintenance to regain their luster and shine, because just like silverware, brass tends to oxidize.

Don't worry, using specific products will make them look like new.

In a general way :

Do not put them in the dishwasher and avoid water.

Use a product for brass such as the special copper and brass mirror (red bottle), easily available on the market.

Clean lightly with a drop of product, avoiding etching if inked, then wiping well with a fine cloth.

For grained brass: a very small drop will suffice, rub very gently with a soft cloth around the engraving.

Brass, like silverware, can oxidize over time, but if you wipe it down from time to time with Miror, or a specific brass product, it will regain its full splendor.