About how long did Metallica spend recording The Black Album?

Metallica spent about eight months recording The Black Album.

The sessions began in October 1990 and continued into 1991, with the main work taking place at One on One Recording Studios in Los Angeles. The band also recorded for about a week at Little Mountain Sound Studios in Vancouver, adding another location to the production story.

The extended schedule reflected the band's demanding standards and the unfamiliar working relationship with producer Bob Rock. Rock challenged Metallica to refine its arrangements, record tighter performances, and create a more powerful studio sound. The musicians were not always happy with his methods, but the process produced a record that was both heavy and unusually accessible.

Eight months refers to the recording period, not the entire album campaign. The album's lead single arrived in July 1991, and the completed record followed in August. Mixing, mastering, artwork, promotion, and touring were separate stages after the core recording sessions.