| Names | |
|---|---|
| IUPAC name tung oil | |
| Other names China wood oil; lumbang oil; tung oil; tungmeal; tungoel | |
| Identifiers | |
| ChemSpider |
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| ECHA InfoCard | 100.029.338 |
| EC Number |
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| UNII | |
| Properties | |
| Density | 0.937 g/ml at 25°C |
Refractive index (nD) | 1.52 (20°C) |
| Hazards | |
| Flash point | >110°C |
Except where otherwise noted, data are given for materials in theirstandard state (at 25 °C [77 °F], 100 kPa). | |
Tung oil orChina wood oil is adrying oil obtained bypressing theseed from thenut of thetung tree (Vernicia fordii). Tung oil hardens upon exposure to air (throughpolymerization), and the resulting coating is transparent and has a deep, almost wet look. Used mostly for finishing and protecting wood, after numerous coats, the finish can even look plastic-like. Related drying oils includelinseed,safflower,poppy, andsoybean oils.[1] Raw tung oil tends to dry to a fine, wrinkled finish. This property was used to make wrinkle finishes, usually by adding excess cobalt drier. To prevent wrinkling, the oil is heated to gas-proof it (also known as "boiled").
"Tung oil finish" is often used by paint and varnish manufacturers as a generic name for any wood-finishing product that contains the real tung oil or provides a finish that resembles the finish obtained with tung oil.[2]
The word "tung" is etymologically derived from the Chinese 桐tóng.[3] The tung oil tree originates in southern China and was cultivated there for tung oil, but the date of cultivation remains unknown.[4] The earliest references for Chinese use of tung oil are in the writings ofConfucius (551–479 BCE) around 500 to 479 BC.[5][6][7][8] During theSong dynasty (960–1279), tung oil was used forwaterproofing on ships.[9]
| Alpha-eleostearic acid | 82.0% |
| Linoleic acid | 8.5% |
| Palmitic acid | 5.5% |
| Oleic acid | 4.0% |
The primary constituent is afatty acid with a chain of 18 linked carbon atoms ormethylene units containing threeconjugateddouble bonds. They are especially sensitive toautoxidation, which encouragescross linking of neighbouring chains, hence hardening of the base resin.
Tung oil is a common traditional wood finish, used typically for two main properties: first, it is a naturally derived substance. Second, after it cures (5 to 30 days, depending on weather/temperature), the result is a very hard and easily repaired finish, so it is used on boat decks and now on floors. The oil is often diluted with hydrocarbon thinner so itsviscosity is very low and enables the oil to penetrate the finest grain woods. This thinning vehicle evaporates in 15 to 20 minutes. When applied in many fine/thinner coats over wood, tung oil slowly cures to a matte/light satin look with slight golden tint. Tung oil resists water better than any other pure oil finish and does not darken noticeably with age. It is claimed to be less susceptible to mould than linseed oil.[11] It is considered safe to be used on sculptures made near waterways.[12]
Heating tung oil to about 500 °F (260 °C)[13] in an oxygen-free environment will substantially increase the viscosity and film-forming quality of the product. Most polymerized tung oils are sold mixed with mineral spirits to make them easier to work with.[citation needed]Limonene and D-limonene are less toxic alternatives for mineral spirits.[citation needed]
Theoil-paper umbrella is the traditional umbrella used inChina,Japan, and other countries in theEast Asian cultural sphere, and was brought to Western countries through theSilk Road. Tung oil is the "oil" mentioned in the oil-paper umbrella,[citation needed] which is used to protect the paper from getting wet, and to make the umbrella waterproof.
The traditional technique for applying pure tung oil is to dilute the oil 1:1 with solvent, then apply a succession of very thin films with a soft, lint-free cloth such as tee-shirt cotton. Diluents range from traditional spirits ofturpentine to any of the newcitrus-based thinners tonaphtha. The choice of thinner should be guided by how fast the coating needs to set. Naphtha works well in spray-on applications in well-ventilated studios. Primary coats may be laid down at a 1:1 oil-to-thinner ratio, and successive layers, if not absorbed into the wood, at higher solvent to oil concentrations. This technique brings out the deepest color of the wood while maintaining amatte finish.
Tung oil finishes that start withpolymerized oils or tung oil preparations are best applied in thefat over lean principle: thinned pure oil is applied to deeply penetrate the surface, to fill pores. Straight oil is then applied moderately to adhere to the surface and provide a good base for the thick gloss layers. The polymerized oil is then applied thickly as a single layer, allowed to fully dry, buffed smooth with very finesandpaper and 0000steel wool. The surface is wiped clean with a moistened rag and allowed to dry. A final coat is applied fairly thickly (the oil will smooth itself into a glass-like coating) and allowed to dry for two to three days. Rags soaked with tung oil canspontaneously combust (burst into flame).[14]
