banked fire; live charcoal covered with ash
Refers to charcoal that is kept smoldering under ash for later use, a traditional method to preserve fire.
The banked charcoal in the hearth remained alive until morning.
If you keep live charcoal banked in the brazier, you can boil water anytime.
熾き refers to glowing embers or live coals, often without the ash covering implied by 活け炭.
Standard kanji spelling for banked charcoal.
Alternate kanji spelling using 埋ける (to bury), emphasizing the ash-covered state.
Compound of 活け (ike, 'keeping alive') + 炭 (sumi, 'charcoal'), with rendaku voicing to zumi. The spelling 埋け炭 uses 埋ける (ikeru, 'to bury') to emphasize the ash-covered state.