|Stylistic origins||Heavy metal, doom metal, grunge, hardcore punk, noise rock|
|Cultural origins||Mid 1980s|
|Typical instruments||Electric guitar, bass, drums, keyboards, vocals|
|Southern sludge - Stoner sludge|
|Southern United States|
|Stoner rock - Post-metal - Alternative metal|
Sludge metal (sometimes referred to simply as "sludge") is a subgenre of heavy metal that melds elements of doom metal and hardcore punk and sometimes incorporates influences from grunge and noise rock. Sludge metal is typically harsh and abrasive; often featuring shouted or screamed vocals, heavily distorted instruments and sharply contrasting tempos. While the style was anticipated by the Melvins from Washington, many of its earliest pioneers were from the city of New Orleans.
Sludge metal generally combines the slow tempos, heavy rhythms and dark, pessimistic atmosphere of doom metal with the aggression, shouted vocals and occasional fast tempos of hardcore punk. As The New York Times put it, "The shorthand term for the kind of rock descending from early Black Sabbath and late Black Flag is sludge, because it's so slow and dense." Many sludge bands compose slow-paced songs that contain brief hardcore passages (for example, Eyehategod's "Depress" and "My Name Is God"). Mike Williams, a founder of the sludge style and member of Eyehategod, suggests that "the moniker of sludge apparently has to do with the slowness, the dirtiness, the filth and general feel of decadence the tunes convey". However, some bands emphasize fast tempos throughout their music. The string instruments (electric guitar and bass guitar) are downtuned and heavily distorted and are often played with large amounts of feedback to produce a thick yet abrasive sound. Additionally, guitar solos are often absent. Drumming is often performed in typical doom metal fashion. Drummers may employ hardcore D-beat or double-kick drumming during faster passages, or through the thick breakdowns (which are characteristic of the sludge sound). Vocals are usually shouted or screamed, and lyrics are generally pessimistic in nature. Suffering, drug abuse, politics and anger towards society are common lyrical themes.
Many sludge metal bands from the Southern United States incorporate Southern rock and blues influences, although not all sludge bands share this style. There is some controversy as to whether the term refers to only the style emerging from New Orleans and later the American South more broadly, or to "a complete consciousness in the heads of like-minded Black Flag/Black Sabbath influenced scenes and individuals all over the world". So-called "atmospheric" sludge bands adopt a more experimental approach and compose music with an ambient atmosphere, reduced aggression and philosophical lyrics. Due to the similarities between sludge and stoner metal, there is often a crossover between the two genres, but sludge metal generally avoids stoner metal's usage of psychedelia. Sludge metal also bears some musical and lyrical resemblance to crust punk, due to the usage of political lyrics and thick, "dirty" guitar sounds.
Along with Black Flag and Black Sabbath, musicians cited by pioneers of the style as influential include Mississippi John Hurt, Lynyrd Skynyrd, Greg Ginn, Trouble, Carnivore, Saint Vitus, Gore, Righteous Pigs, Amebix and Swans. Early sludge metal groups also borrowed from the industrial music of SPK, Throbbing Gristle, Chrome and Swans. The beginnings of sludge have been traced to the "slow punk" of Flipper and Black Flag's album My War.
Perhaps the most significant influence was Melvins, a band from the state of Washington. Their earliest releases, Six Songs (1986) and Gluey Porch Treatments (1987), are often regarded as the first sludge records. At this time, the band was also an important member of Washington grunge scene. Another prominent band from the Washington grunge scene, Alice in Chains have also been influential to early sludge metal with their second album Dirt. Neurosis, from Oakland, were also significant early practitioners.
At the beginning of the 1990s, a number of bands from Louisiana (particularly New Orleans with its metal scene) took these influences and developed the style that would be known as sludge. Eyehategod (formed in 1988), Crowbar (formed in 1989 as The Slugs) and Acid Bath (formed in 1991) pioneered this movement. On the East Coast, Buzzov*en (formed in 1989), 16 (formed in 1990) and Grief (formed in 1991) adopted a slower-paced approach to the emerging genre.
According to Phil Anselmo,
Back in those days, everything in the underground was fast, fast, fast. It was the rule of the day. But when the Melvins came out with their first record, Gluey Porch Treatments, it really broke the mold, especially in New Orleans. People began to appreciate playing slower. With that, all the old Black Sabbath came back around and then you start digging and you come to your Saint Vitus, your Witchfinder General, your Pentagram, etc.—
Sludge metal subsequently spread throughout the Southern and Eastern United States.
Jose Carlos Santos notes a focus shift as a result of the impact of the British group Iron Monkey's first album in 1997:
Coincidence or not, it seemed like the sludge floodgates opened to the rest of the world, and in the past decade small pockets, or mini-scenes, can be spotted in just about any country you'd care to mention.—
These include the Japanese group Corrupted and contemporary American groups such as Dumb Numbers, Lair of the Minotaur, Old Man Gloom and Kylesa. In addition, the U.S. state of Georgia has been identified as major sources of new sludge groups such as Mastodon, Baroness, Black Tusk, and Kylesa.
During the late 1990s, many sludge metal bands began to incorporate post-rock elements into their music. This new sound, referred to as "post-metal", was greatly inspired by the experimental style of Neurosis during the early to mid 1990s, and is performed by prominent bands such as Isis, Cult of Luna and Pelican.
Traditional/Southern sludge metal
These bands are the pioneers of the genre or are strongly influenced by those bands. Many are from the Southern United States, excluding the Melvins who are from Montesano, Washington and Iron Monkey who are from England.
- Acid Bath
- Corrosion of Conformity
- Crowbar (formed in 1989 as The Slugs)
- Iron Monkey
- Superjoint Ritual
Stoner sludge metal
These bands have mixed typical stoner metal traits with typical sludge metal traits, and may be considered a part of both genres.
- Electric Wizard
- High on Fire
- Mico de Noche
Other fusions with sludge metal
- Alice in Chains (sludge metal, alternative metal and hard rock)
- Baroness (sludge metal and progressive metal)
- Black Label Society (sludge metal, hard rock and Southern rock)
- Black Tusk (sludge metal, hardcore punk and stoner rock)
- Boris (sludge metal and drone metal)
- Cancer Bats (sludge metal, hardcore punk and southern rock)
- Dumb Numbers (sludge, doom, noise rock, "swooning feedback pop") 
- Fudge Tunnel (sludge metal, noise rock and alternative metal)
- Helms Alee (sludge metal and shoegaze)
- Isis (sludge metal and post-rock)
- KEN Mode (sludge metal, noise rock and post-hardcore)
- Kingdom of Sorrow (sludge metal and metalcore)
- Lair of the Minotaur (sludge metal and thrash metal)
- Mastodon (sludge metal, progressive metal and alternative metal)
- Mistress (sludge metal and death metal)
- Part Chimp (sludge metal and noise rock)
- Soilent Green (sludge metal and grindcore)
- Will Haven (sludge metal and metalcore)
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