ʻO ka wai waihoʻoluʻu paʻakikī metala kekahi ʻohana o nā mea pena i loaʻa nā metala i hui pū ʻia me ka ʻāpana organik.He nui nā mea hoʻonaʻokoʻa azo, ʻoi aku ka nui o nā mea i loaʻa mai nā naphthols, e hana i nā paʻakikī metala ma o ka hoʻopili ʻana i kekahi o nā kikowaena azota azo.ʻO nā kala paʻakikī metala nā mea pena i hoʻopaʻa ʻia e hōʻike ana i ka pili nui i nā fiber protein.I loko o kēia mea pena, ua hui pū ʻia hoʻokahi a i ʻole ʻelua mau molekule wai me ka ion metala.ʻO ka mole kala ka mea maʻamau he ʻano monoazo i loaʻa nā hui hou e like me ka hydroxyl, carboxyl a i ʻole amino, i hiki ke hana i nā paʻakikī hoʻonohonoho ikaika me nā ion metala hoʻololi e like me ka chromium, cobalt, nickel a me ke keleawe.