Copper develops a patina with use. In the case of copper pots and pans, the patina can make the pan look fairly dirty because of the uneven coloration of the patina, and removing the patina is standard. However, the situation is different for copper sinks. These often end up with a dark brown patina that is often more uniform in appearance and that serves as a protective layer; this is a patina that you want to have. If you want to install a copper sink, you need to know how to care for the patina -- and when to increase or halt its formation.
You Choose the Level
Copper patinas are not equal. One sink may end up with a patina that looks like a very dark copper color, while others may end up with a more chocolate-like color. The foods and cleaning agents you use in the sink can also affect the color of the patina and leave brighter or darker spots. You actually get to choose the level of patina in your sink; there are special additives that you can use to darken spots, and you can wax the copper sink when it reaches a color that you like.
Note that foods like tomato sauce can lighten the patina, resulting in a patchy look. In that case, you can wax the portions you want to keep at a certain color and let the lighter parts darken over time, waxing those when they match the rest of the surface.
It's Natural but Not Necessarily Required
Patinas are natural and should be expected and cultivated. Remember that you choose the color at which you want to suspend the patina's growth, so if you want, you can have a light patina. The patina is protective, but with the waxes and sealants available for copper sinks now, a dark patina isn't required. It may be too much work to keep the sink a very shiny, original copper color, though, so allowing at least a light patina to form is easier.
These Sinks Require Patience
Copper has what's commonly called a living finish because the patina constantly changes. Achieving an even patina, especially when you're trying to make lighter spots match darker areas, takes time. Have patience and keep checking the sink, being ready to seal or wax the surface when appropriate.
If you'd like more help guiding the patina in your sink toward a specific shade, speak with the company that made the sink. They can help you with preventing spots and creating that even shade that looks so good.