Brass substrate is electroplated with 18k gold and then dipped into acid to create the subtly destroyed surface. The concentration of the plating solution, air temperature and time in the acid bath all play integral roles in the final result and exist in a delicate balance. No two items are the same and these nuances / variations should be seen as a characteristic of the product.
Black Sterling is acheived by the oxidization of sterling silver. This blackened state will fade or scratch off over time but we will be happy to help teach you how to re-oxidize your pieces if you are interested (it is a very easy process). Additionally, please note that Black Sterling tends to look darker in photograph than in person.