Tung oil
Encyclopedia
| Palmitic acid Palmitic acid Palmitic acid, or hexadecanoic acid in IUPAC nomenclature, is one of the most common saturated fatty acids found in animals and plants. Its molecular formula is CH314CO2H. As its name indicates, it is a major component of the oil from palm trees . Palmitate is a term for the salts and esters of... |
5.5% |
| Oleic acid Oleic acid Oleic acid is a monounsaturated omega-9 fatty acid found in various animal and vegetable fats. It has the formula CH37CH=CH7COOH. It is an odorless, colourless oil, although commercial samples may be yellowish. The trans isomer of oleic acid is called elaidic acid... |
4.0% |
| Linoleic acid Linoleic acid Linoleic acid is an unsaturated n-6 fatty acid. It is a colorless liquid at room temperature. In physiological literature, it has a lipid number of 18:2... |
8.5% |
| alpha-Eleostearic acid | 82.0% |
Tung oil or China wood oil is a drying oil
Drying oil
A drying oil is an oil that hardens to a tough, solid film after a period of exposure to air. The oil hardens through a chemical reaction in which the components crosslink by the action of oxygen . Drying oils are a key component of oil paint and some varnishes...
obtained by pressing the seed
Seed
A seed is a small embryonic plant enclosed in a covering called the seed coat, usually with some stored food. It is the product of the ripened ovule of gymnosperm and angiosperm plants which occurs after fertilization and some growth within the mother plant...
from the nut
Nut (fruit)
A nut is a hard-shelled fruit of some plants having an indehiscent seed. While a wide variety of dried seeds and fruits are called nuts in English, only a certain number of them are considered by biologists to be true nuts...
of the tung tree
Tung tree
Vernicia fordii is a species of Vernicia in the spurge family, native to southern China, Burma, and northern Vietnam. Other vernacular names include Tung Oil Tree, Tung-oil Tree, Tungoil Tree, China Wood-Oil Tree, Kalo Nut Tree, 油桐 Vernicia fordii (Tung Tree; syn. Aleurites fordii Hemsl.) is a...
(Vernicia fordii). As a drying oil, tung oil hardens (dries) upon exposure to air. The resulting coating is transparent plastic
Plastic
A plastic material is any of a wide range of synthetic or semi-synthetic organic solids used in the manufacture of industrial products. Plastics are typically polymers of high molecular mass, and may contain other substances to improve performance and/or reduce production costs...
-like and is exploited in most of its applications, which include wood finishing
Wood finishing
Wood finishing refers to the process of embellishing and/or protecting the surface of a wooden material. The process starts with surface preparation, either by sanding by hand , scraping, or planing. Imperfections or nail holes on the surface may be filled using wood putty or pores may be filled...
and the composition of oil paint
Oil paint
Oil paint is a type of slow-drying paint that consists of particles of pigment suspended in a drying oil, commonly linseed oil. The viscosity of the paint may be modified by the addition of a solvent such as turpentine or white spirit, and varnish may be added to increase the glossiness of the...
s and printing inks. Related drying oils include linseed
Linseed oil
Linseed oil, also known as flaxseed oil, is a clear to yellowish oil obtained from the dried ripe seeds of the flax plant . The oil is obtained by cold pressing, sometimes followed by solvent extraction...
, safflower, poppy
Poppyseed oil
Poppyseed oil is an edible oil from poppy seeds . The oil has culinary and pharmaceutical uses, as well as long established uses in the making of paints, varnishes, and soaps.Poppy seeds yield 45–50% oil...
, and soybean
Soybean oil
Soybean oil is a vegetable oil extracted from the seeds of the soybean . It is one of the most widely consumed cooking oils. As a drying oil, processed soybean oil is also used as a base for printing inks and oil paints...
. The oil and its use are believed to have originated in ancient China, and appear in the writings of Confucius
Confucius
Confucius , literally "Master Kong", was a Chinese thinker and social philosopher of the Spring and Autumn Period....
from about 400 B.C.
Raw Tung oil tends to dry with a fine wrinkled finish, the US name for this is Gas Checking, this property is used to make Crystal finishes. To stop this, the oil is heated to gas proof it and most oils used for coating are gas-proofed. This property was used to make wrinkle finishes, usually by adding excess cobalt drier.
The name is often used by paint and varnish as a generic name for any wood finishing product that contains the real tung oil and/or provides a finish that resembles that obtained with it.
Wood finishing
Tung oil has become popular as an environmentally friendly wood finish, but it should be noted that many products labelled as "tung oil finishes" are deceptively labelled: polymerized oils, wiping varnishes, and oil/varnish blends have all been known to be sold as tung oil finishes (sometimes containing no tung oil at all), and all the above contain solvents and/or chemical driers. Product packaging will usually clearly state if it is pure tung oil, so there is a good chance you will be buying something else if the sales literature is vague.
Heating tung oil to about 500 degrees in an oxygen-free environment will substantially increase the viscosity and film-forming quality of the product. The resulting polymerized tung oil will range in consistency from that of maple syrup to that of motor oil. Most polymerized tung oils are sold mixed with mineral spirits to make them easier to work with. Limonene
Limonene
Limonene is a colourless liquid hydrocarbon classified as a cyclic terpene. The more common D isomer possesses a strong smell of oranges. It is used in chemical synthesis as a precursor to carvone and as a renewably-based solvent in cleaning products....
and D-limonene are less toxic alternatives for the mineral spirits.
Application
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 non-fuzzy cloth such as tee-shirt cotton. Dilutants range from traditional spirits of turpentineTurpentine
Turpentine is a fluid obtained by the distillation of resin obtained from trees, mainly pine trees. It is composed of terpenes, mainly the monoterpenes alpha-pinene and beta-pinene...
to any of the new citrus-based thinners to naphtha
Naphtha
Naphtha normally refers to a number of different flammable liquid mixtures of hydrocarbons, i.e., a component of natural gas condensate or a distillation product from petroleum, coal tar or peat boiling in a certain range and containing certain hydrocarbons. It is a broad term covering among the...
. 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 a matte
Matte
Matte may refer to:In film:* Matte , filmmaking and video production technology* Matte painting, a process of creating sets used in film and video* Matte box, a camera accessory for controlling lens glare...
finish.
Tung oil finishes that start with polymerized
Polymerization
In polymer chemistry, polymerization is a process of reacting monomer molecules together in a chemical reaction to form three-dimensional networks or polymer chains...
oils or tung oil preparations are best applied in the fat over lean
Fat over lean
Fat over lean refers to the principle in oil painting of applying paint with a higher oil to pigment ratio over paint with a lower oil to pigment ratio to ensure a stable paint film, since it is believed that the paint with the higher oil content remains more flexible.Oil paint dries at different...
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, is buffed smooth with very fine sandpaper
Sandpaper
Sandpaper, also known as glasspaper, is a heavy paper with abrasive material attached to its surface.Sandpaper is part of the "coated abrasives" family of abrasive products. It is used to remove small amounts of material from surfaces, either to make them smoother , to remove a layer of material...
, then 00 steel wool
Steel wool
Steel wool, also known as wire wool, is a bundle of strands of very fine soft steel filaments, used in finishing and repairing work to polish wood or metal objects, and for cleaning household cookware....
. The surface is wiped clean with a moistened rag, then 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. The resulting finish is almost completely impervious to water.
Food contact and allergic reactions
As the source of tung oil is a nut, people with nut allergies often report adverse reactions to contact with (or even the odour of) tung oil. Reactions can be severe in some cases. While tung oil has been used for many centuries as a finish for kitchen items such as wooden bowls and cutting boards, some individuals must avoid its use.Other uses
As the penetrating power of tung oil is excellent and it will adhere to porous minerals, it is often used by stonemasons on granite or marble installed in kitchens, bathrooms, and other staining fluid environments. Applied at a 1:5 ratio (oil to naphthaNaphtha
Naphtha normally refers to a number of different flammable liquid mixtures of hydrocarbons, i.e., a component of natural gas condensate or a distillation product from petroleum, coal tar or peat boiling in a certain range and containing certain hydrocarbons. It is a broad term covering among the...
), it seals the surfaces permanently, while also giving a finish like that of wet stone to the product. Often several thin layers are applied at the high solvent-to-oil ratio, in order to build up the durability and permanence of the coating. The non-yellowing nature of tung oil is vitally important for its satisfactory use in these applications.