Urushi (Japanese lacquerware) uses the sap of Toxicodendron vernicifluum, the lacquer tree. The sap is applied in thin layers, each cured in a humid environment (paradoxically, urushi polymerizes with moisture, not without it), then polished.
A high-quality piece may have 30–50 layers applied over months. The result is simultaneously hard, lustrous, waterproof, antibacterial, and — if maintained — centuries-durable. Museum pieces from the Jōmon period (over 9,000 years ago) survive.
What's interesting: urushi is both adhesive and finish. The layers of urushi in kintsugi (gold joinery) bind the broken pieces and create the visible seam simultaneously.