Black One is the fifth album by Sunn O))). It is a combination of both experimental and traditional Sunn O))), utilizing many guest musicians, including black metal musicians Malefic and Wrest from Xasthur and Leviathan, respectively. The band supposedly also went so far as to lock the claustrophobic Malefic in a casket to record the vocals on "Báthory Erzsébet".
2,000 copies included a bonus disc titled Solstitium Fulminate, containing a mix of live performances recorded at Roskilde in 2005 and the immediately preceding European tour.
"Orthodox Caveman", previously known as "Caveman Salad", is based on live material from the White (see Live White) tour. "Báthory Erzsébet" was recorded as a tribute to Quorthon (as well as the countess who inspired Bathory's name) and, according to an interview with Terrorizer Magazine, is loosely built "around a really slowed down riff from 'A Fine Day to Die'".
The album is not a continuation of the White1 and White2 style. As the band has repeatedly stated, the title is written as the word "one", not the digit.