Union of Darkness

A Union of Darkness was the name given to Sith weddings. They were most often held on Korriban, in the Valley of the Dark Lords, though it wasn't required. However, it was required that a deceased Sith Lord perform the ceremony, or else the union would not be recognized. It was also customary to wear decorations and jewelry made from sacrifices.

A Typical Ceremony
The Slicing (Man and woman cut themselves, usually in the chest region.) The Bleeding (The participants would each take a silver goblet, and have their blood flow into it.) The Joining (The couple would then drink the blood of their partner.)

Known Unions
Epin Lanmaw and Karana Selria, performed by Darth Traya.