The Vietnamese have known the techniques of lacquer work since ancient times when it was used for the waterproofing of barges. Under the reign of Le Nhan Ton (1443-1460) the technique also became used for decorative items. Lacquerware is an incredibly time consuming art form. Lacquer itself is a natural resin that is found by tapping the cay son tree. It is milky-white in its natural state, and is made black by mixing with resin for over forty hours in an iron container. The iron oxide blackens the lacquer, and the resin gives it a gloss. The process begins after finding the correct wood which is then coated, filled and sanded over several weeks time. The lacquering art itself requires ten base coats, and each coat takes one week to dry and then must be sanded before the next coat is applied. A specially prepared fine lacquer which has been blackened by the iron-oxide is required for the eleventh coat. During this stage, no dust may touch the object, and the final sanding coat is done with fine coal powder and whitewash. The workers polish the surface with their palms until it becomes shiny.