godan verb (-ru), intransitive verb
become black; blacken
Intransitive; describes something turning black or dark, often from burning, soiling, or aging. Less common than 黒くなる in everyday speech.
火事で壁が黒まってしまった。
The wall blackened from the fire.
長年使った鍋の底が黒まっている
The bottom of the pot has become black from years of use.