Caring for your copper sink is surprisingly easy, they’re virtually maintenance free. For basic cleaning simply use a mild soap and water—other cleaners are not necessary.

The one precaution we advise is to avoid leaving harsh chemicals and acidic foods in a copper sink. These can temporarily lighten a copper sink’s patina finish—whether a natural patina or an applied patina finish. Therefore, we recommend you avoid using harsh chemicals or abrasive materials on any copper products. With the exception of a SoLuna Matte Copper sink that you want to remain shiny, don’t use copper polish on any copper sink.

Regardless of which SoLuna patina you choose, a copper finish is a living finish and never really stops changing in color. The gradual evolution of a copper finish is an interesting process. As the surface ages and mellows it becomes even more handsome. If you like, you can greatly reduce this change with the use of wax...

For more info got to: http://www.coppersinksonline.com/copper-sinks-maintenance.aspx

Here is also a great blog that goes over the difference and how to take care of a copper sink:
http://moxie-girl.com/blog/how-to-clean-a-copper-sink/