黑板
hēi bǎn · HSK 2
blackboard
⬛ 黑板 = 黑 (black) + 板 (board/plank)
黑 means black; 板 means board or plank — together they name the classroom blackboard. 板 also shows up in 木板 (wooden board) and 老板 (boss, literally old board).
黑 — top 里 over 灬 (fire) — soot from flame
Originally a pictograph of a person whose face was blackened by smoke from a fire, with the lower 灬 representing flames and the upper part showing soot stains. Over time the form was regularized into the modern shape, and the meaning broadened from 'soot-blackened' to the general color black.
板 — wood radical 木 + 反 (fǎn, phonetic)
板 is a semantic-phonetic compound. The 木 'wood' radical signals the meaning — a flat piece of wood, i.e. a board or plank. The right side 反 supplies the sound, historically close to 'bǎn/pàn'. Over time it extended to mean any flat panel, and figuratively 'stiff' or 'inflexible'.