Granular urea (CO(NH₂)₂) — the modern, purified form of the nitrogen compound found in urine. Historically, stale urine provided the ammonia needed for woad and indigo fermentation vats, fulling cloth, and tanning leather. Today granular urea serves the same chemistry: it hydrolyzes to ammonia in water, creating the alkaline reducing environment that makes indigo soluble for vat dyeing. Also used as high-nitrogen fertilizer (46-0-0).