Kanohi

"You must not remove your masks, unless you are replacing one with another. Without them, your strength is halved."

- Toa Helryx, BIONICLE Legends 10: Swamp of Secrets

Kanohi were power-imbued masks worn by various bio-mechanical species in the Matoran Universe. Kanohi came in many shapes and had varying powers and power levels. They were forged using either molten Protodermis or Kanoka disks. Matoran and Turaga would die or go into a coma if their masks were kept off for too long, while Toa and other powerful beings would be severely weakened if their Kanohi were removed; Makuta in particular relied on their Kanohi to contain their Antidermis. The natural color for most Kanohi was a dull silver-grey; when worn, they would change color to match the armor of their wearer. This did not apply to legendary masks or those of immense power, like the Avohkii.

Powerless Kanohi
Powerless Kanohi were basic Kanohi, with no powers whatsoever. Matoran had to wear these Kanohi, or else they would slowly get weaker and eventually go into a coma-like state. These type of Kanohi were forged from Kanoka with a power level of 6 or lower, as the power was siphoned off in the forging process. On Metru Nui, powerless masks were denoted by having silver streaks painted on the top; on Mata Nui, these marks eventually faded away under the sun.

Noble Kanohi
Noble Kanohi were masks that contained powers, although they were less powerful than their Great counterparts. These were most commonly worn by Turaga, though their powers could also be used by a Toa. They were forged from Level 7 Kanoka disks, but could also be created when a Toa became a Turaga, from the Toa's original Kanohi. Noble masks that were forged were then denoted by having the top painted black.

Great Kanohi
Great Kanohi were masks with powers on a greater level than Noble Kanohi. They were the most commonly seen type, after powerless masks. They were worn by Toa and other powerful beings, such as the Makuta and Order of Mata Nui members. They could be forged from level 8 Kanoka disks. They could also be created when a Matoran became a Toa, their powerless Kanohi becoming Great Kanohi. Great Kanohi were usually silver-grey when not worn, and upon being donned would change their color to match the armor of its new wearer.

Kanohi Nuva
Kanohi Nuva were a special type of Kanohi collected and worn by the Toa Nuva. They possessed even greater powers than ordinary Great Kanohi and could also allow its wearer to share its powers with others if they were within a close proximity, but the Kanohi could only be activated by Toa Nuva.

Legendary Kanohi
Legendary Kanohi were very powerful masks, and were sought by many beings. The Kanohi Ignika, the Mask of Creation and the Kanohi Vahi were the only known Legendary Kanohi in existence.

Links
http://web.archive.org/web/20031003182246/www.lego.com/eng/bionicle/masks.asp?type=kanohi

Kanohi