A black, brittle, and porous form of carbon, usually the residue of partially burned wood. In ancient times it was made by covering a pile of wood with earth and burning it slowly for several days with only a sufficient amount of air to burn off the gases. This practice left behind a relatively pure form of carbon. It was a time-consuming process requiring careful supervision, but charcoal was a favored fuel when intense, sustained heat without smoke was desired. There is no evidence that natural mineral coal was used in ancient Israel.
Charcoal, in an open fire or in a brazier, was used to warm oneself in cold weather. (Isa 47:14; Jer 36:22; Joh 18:18) Its even heat with an absence of flame and smoke also highly recommended it for cooking. (Joh 21:9) For smelting and refining metals, charcoal was indispensable; without it, reaching and sustaining the great temperatures required to reduce the ores to pure metals was hardly possible. (Isa 44:12; 54:16; see REFINE, REFINER.) Much the same as is done today in charging an iron blast furnace, the ore was sandwiched in between layers of charcoal. This practice apparently gave rise to the proverb: Kindness toward an enemy is like coals of fire upon his head; it softens his anger and brings out the good in him. (Pr 25:22; Ro 12:20) The glow of slow-burning charcoal was used by the “wise woman” of Tekoa as an illustration of living posterity.—2Sa 14:1-7.
However, the Hebrew words ga·cheʹleth and pe·chamʹ are not always rendered “charcoal,” for they often simply refer to coals, burning coals, or embers. Wood was used as fuel for the tabernacle altar (Le 1:7, 8; 3:5), and on the Day of Atonement “burning coals of fire from off the altar” made the incense overspread the ark of the covenant like a cloud. (Le 16:12, 13) Isaiah described the idolater that makes a god out of part of the same tree with which he builds a fire, the coals of which bake his bread.—Isa 44:14, 15, 19.
In a number of Scripture passages “coals” are used in a somewhat figurative or illustrative sense, indicating any kind of glowing, hot, burning substance. (2Sa 22:9; Job 41:21; Ps 18:8, 12, 13; 140:10; Isa 6:6; Eze 1:13; 10:2; 24:11) The hot “burning coals of the broom trees” were used to represent the retribution upon one with a “tricky tongue.”—Ps 120:2-4.