黒くろずむ

godan verb (-mu), intransitive verb

blacken; darken; become blackish

Describes something gradually turning black or dark, often with a nuance of soiling, tarnishing, or aging. Common for silver, teeth, walls, or skin.

• 銀ぎんの指ゆび輪わが黒くろずんできた。

  The silver ring has become tarnished.

• 長なが年ねん使つかった壁かべが黒くろずんでいる。

  The wall, used for many years, has darkened.