dirt; disgrace

limescale

greasy dirt

dirt; grime

dental plaque; tartar

deeply accumulated filth

earwax

tea stain (on the inside of a tea pot, tea cup etc)

dried nasal mucus; booger

see 含垢忍辱[han2 gou4 ren3 ru3]

pure of heart

to hide dirt, to conceal corruption (idiom); to shelter evil people and accept wrongdoing; aiding and abetting wicked deeds