Traditional lacquerware uses sap from Melanorrhoea usitata trees. Chemical analysis revealed the sap polymerizes into a natural plastic harder than modern synthetic lacquers.
Gerd Eichmann, CC BY-SA 4.0
The Chemistry of a Natural Polymer
The remarkable durability of Bagan's traditional lacquerware begins with thitsi, the sap of the Melanorrhoea usitata tree, a relative of the poison ivy plant native to Southeast Asia. This sap is an oleo-resin, a complex natural emulsion containing water, proteins, gummy substances, and the chemical compounds responsible for its properties: catechol lipids called "thitsiol". Thitsiol is structurally similar to urushiol, the allergenic compound in poison ivy, which explains why the raw sap can cause a severe skin rash.
The transformation from a milky liquid sap into a hard, glossy coating is a process of oxidative polymerization. This chemical reaction is catalyzed by a natural enzyme within the sap called laccase. When the sap is applied to a surface and exposed to the air, the laccase enzyme uses oxygen to create reactive free radicals from the thitsiol molecules. These radicals then attack neighboring thitsiol molecules, causing them to link together and form a dense, cross-linked polymer network. This process is not like the simple evaporation of a solvent; it is a chemical change that creates a new substance—a natural plastic.
A Bioplastic Tougher Than Synthetics
The curing process for lacquerware is precise and requires a specific environment. Artisans in Bagan have known for centuries that the polymerization requires high humidity, typically 70-87%, and warm temperatures between 27-31°C. These conditions are optimal for the laccase enzyme to function efficiently. Workshops often use underground cellars, or sayit, to maintain this stable, humid environment, allowing each thin layer of lacquer to cure properly over several days before the next is applied. A finished piece might have between 7 and 16 layers of this hardened resin.
The resulting natural polymer is exceptionally robust. Once cured, the cross-linked thitsiol structure is waterproof and resistant to insects, and can withstand damage from acids, alkalis, and alcohol. The hardness and glossy finish of this natural material are superior to many synthetic coatings. Scientific analysis using nanoindenters and atomic force microscopy has quantitatively confirmed the exceptional physical properties of this traditional material. The final product shows a sophisticated understanding of natural chemistry, perfected long before the invention of modern polymers.
💡Fun Facts
The main active compound, thitsiol, is a catechol derivative closely related to urushiol, the irritant found in poison ivy and poison oak.
The deep black color of some lacquerware is not from a pigment, but from a chemical reaction where the thitsiol chelates with iron ions, often introduced by stirring the sap with an iron tool.
The hardening process is entirely dependent on the laccase enzyme; if the sap is heated too much, the enzyme denatures and the sap will not polymerize correctly.
The earliest lacquerware fragments found by archaeologists in Bagan date back to the 13th century.
