Updated December 2010 -  Referred to by Confucius as early as 400BC and also known as China Wood Oil, Tung Oil is believed by many to be the finest natural wood finish in the world. It is extracted from the nuts of the Tung Tree - Aleurites fordii - native to east Asia. Legend has it that the Great Wall Of China was sealed with tung oil. It is a component of many products marketed as Tung Oil but which are usually extended with other cheaper oils and also contain added toxic driers and anti-fungals.

Tung oil is a safe to use, tree nut oil which polymerises naturally and cures to a tough, water resistant, beautiful finish which patinates better than skin finishes.

Click HERE to see purchase options for Tung Oil.

OIL FINISH or MEMBRANE FINISH

The great majority of Wood finishes can be grouped as either OIL or MEMBRANE finishes.

Membrane or skin finishes include varnishes, shellacs (French polish) and lacquers. These finishes divide further into those which can be re-formulated on the fly, where the newly applied finish can meld with the prior coating, (for example lacquer and shellac), or those modern varnishes which polymerise (cross link) and which have to be removed, or at least heavily scuffed (sometimes referred to as giving the surface "tooth"), to provide a key for subsequent coats or touch up. (It is precisely this final stage inertness and imperviousness resulting from the completion of the cross linking chemical bond formations that makes these modern polyurethanes - either moisture or catalyst cured - so resistant and tough). They do however usually scratch rather easily.

Oil finishes by comparison, for whatever end, flooring, cabinetry etc, are by nature more penetrative and mostly "in the wood" whereas membrane or skin finishes typically sit on the wood and key with the wood with a lesser degree of penetration. Oil finishes can be regarded as preserving the look and feel of the wood better than skin finishes which, critics would say, put a plastic coating on the wood.

Oil finishes can be commercial formulations with names such as Danish Oil, Teak Oil, Tung Oil Finish or Buffing Oil.  The precise ingredients and their proportions is typically proprietary information.

As a general statement nut oils derived from trees are, for wood finishing purposes, more robust than seed oils e.g linseed.  The tree nut or seed oils of particular interest to woodfinishing are those which have a "drying" characteristic.  They include Linseed (both Raw and so called Boiled, which is, these days, usually raw with chemical driers added), walnut, poppy seed and tung oils.

These oils can be classed as drying oils and it is this characteristic which makes an oil of interest to wood finishers.  A drying oil is an oil which hardens to a tough, solid film after a period of exposure to air. The term "drying" is actually somewhat of a misnomer - the oil does not harden through the evaporation of water or other carrier solvents as do many skin finish formulations, but through a chemical reaction in which oxygen is absorbed from the environment (autoxidation).

Oil finishes can be remarkably tough, are usually superior in the patination stakes and the initial application, touch-ups or re-coats are far less problematic than with membrane finishes.  Membrane finishes frequently crack when damaged and this allows penetration of moisture and dirt into the ding or crack which then discolours.  Oil finishes have little skin to worry about and thus suffer less from the delamination due to dings and natural seasonal wood movement which is a given for all solid wood in service outside of airconditioned environments. They consequently typically patinate better.

Patina defined - the appearance of a piece, including dents, dings and the aged finish and, while mostly applied to cabinet pieces, also applicable to floors and window and door trim.  Regarded as a positive and desirable attribute easily ruined with unsympathetic restoration.

Tung Oil Application:

It is strongly recommended that Pure Tung is tested on an off-cut or equivalent piece of the wood that the finish is intended for.  This proving process will determine thinning ratios and your technique and will help to be sure that your expectations are in line with what can be achieved. This advice is especially relevant to oiled finishes which, by their nature, can absorb oil deep into the wood and which are therefore unlike skin finishes which can often be more easily removed with strippers or sanding if you change your mind or are unhappy with the outcome.

We recommend using 50:50 tung oil and terpene for initial and subsequent coats. As a general rule, oil finishes (as opposed to membrane finishes) are best applied on work that has been sanded to as fine a grade as is feasible.  Cabinetry pieces for example will benefit from sanding well past 600 grit.  While this is not possible for floors, care with sanding and going to the finest feasible grit is recommended. Apply an initial wash coat of 50:50 thinned oil, wipe off after a few minutes when the oil begins to tack and complete the process over several days with several light coats using this same apply and rub off method.  Some users recommend starting with a quite heavily thinned wash coat to get the initial penetration and, for subsequent coats, use progressively less thinned oil. Intervals between coats should probably be about 24 hours at least, more in rainy or humid weather. Longer intervals between coats is desirable. In service it can be touched up at will with maintenance coats which will not form a sticky build up of old oil. The oil seems to fully harden over about 14 days.

Buffing

We have trade customers who use a mechanical floor buffing machine and report highly attractive, tough and durable results.

Coverage: Any suggestion for coverage is a guess because some wood species are much more thirsty than others and second and subsequent coats will absorb less than the initial coat.  Assuming a 50:50 thinning and work sanded to at least 240 grit, around 18 to 20 square metres per litre is indicated for new (or freshly sanded) work. More highly sanded finishes with second and subsequent coats will require far less oil. After several coats coverages estimates become academic - many dozens of square metres to the litre.

We recommend Citric Terpene (d-Limonene) for thinning. D-Limonene is derived by distillation from orange and mandarin skins and is used as a food flavour. (Note: We are currently unable to supply Citric Terpene. It is naturally derived and the producing countries are in drought).  Gum turpentine is an alternative and is a naturally distilled tree product with a more pleasant odour than the common petrochemically derived mineral turpentine. Note that these thinning products, although 'naturally' derived, still require respect.   Email or Google for an MSDS.  Both are schedule 3 flammable goods so cannot be mailed.  Contact us for supply options.

A few more points:

• Pure tung will, in common with all oil finishes, darken the wood - more so if used straight on the raw wood, less so if used over a sealer.
• When considered for use on floors the floor finishing trades are accustomed to getting floor polishing jobs completed very rapidly and commercially formulated products assist with this efficiency. Pure tung demands a more considered approach.
• For most tradespersons the notion of applying and wiping off a finish is counterintuitive, they will tend to leave the oil to pond which is not the ideal method.
• There is with tung oil no issue of the time window between coats such as applies to some poly-urethane finishes which can require that second and subsequent coats be applied after the solvents in the prior coat have sufficiently off-gassed but before all the chemical bonds have formed in the prior coat.
• Pure tung is NOT a high build "treacle" finish.
• Pure tung is NOT a shiny membrane finish although can be buffed to a quite high lustre.
• Pure tung MUST be applied with thin "wiped off" coats. Do NOT allow the oil to pond or attempt to cure thick coats.
• Pure tung will cure to a very tough finish. After a few days the surface of the treated wood will be remarkably hard and suitable for buffing.
• Tung has, even when used neat, a remarkable affinity for wood and penetrates better than any oil I have used.
• Pure tung takes longer to cure (it has no chemical driers added) especially in rainy or humid weather.
• Tung cures quicker, more completely and to a harder and far less oily finish than linseed oil.
• Tung does not continue to darken over time as may linseed oil.
• Tung is not as likely to support mould as linseed oil.
• At this stage we have no indication of the ability of Tung Oil to withstand UV exposure (feedback from users very welcome).
• Pure Tung can be touched up with maintenance coats or applied to restore areas of high wear with relative ease.
• Applications of pure tung do not demand as clean an environment in terms of airborne dust as do membrane finishes.
• Tung oil is very tenacious and the use of expensive application brushes is not recommended because they are impossible to fully clean.

Uses: Interior cabinetry & woodwork, interior floors, exterior furniture, decks, kitchen benches & wooden kitchen implements & chopping boards, children’s toys.  Pure Tung is  EN71  "toy safe" standard compliant.

Other materials: Tung oil may be highly useful as a sealer on stonework, non glazed terra cotta and marble bench tops. The advice above about testing first is stressed. (feedback from users very welcome).

OH&S Cautions: Pure Tung Oil in non-flammable & can be regarded as non-toxic. Although it smells somewhat like a salad oil it IS NOT to be used for cooking or salad dressing. Due to the slight exothermic property of the oil while curing (a commonplace feature of drying oils), there is a marginal risk that balled oily rags may spontaneously combust - spread application rags out to dry.

• Tung Oil is “Non hazardous” rated by Worksafe Australia Criteria and is able to be mailed
• Pure tung has no UN hazardous goods code
• Specific Gravity at 20 deg.C.    - 0.9375
• Moisture & Impurities             - 0.01%
• Flash Point                           - 288.90 deg. C
• Autoignition Temp.                - 457 deg. C

Advice from users sought

We appreciate all feedback from users.  In particular we would like to know users views on;

• Mould resistance
• UV resistance
• Usefullness on materials other than wood
• Means of tinting the oil (Do spirit-soluble aniline powder dyes work? do earth pigments have any promise?)

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ORIGINS AND INFORMATION RE-CAPS FROM www SOURCES

Tung oil comes from the seeds of several species of Aleurites, primarily Aleurites fordii, a deciduous shade tree native to China. It belongs to the Euphorbia Family (Euphorbiaceae) along with the candlenut tree (A. molucanna), another species with seeds rich in unsaturated oils. For centuries tung oil has been used for paints and waterproof coatings, and as a component of caulk and mortar. It is an ingredient in "India ink" and is commonly used for a lustrous finish on wood. Some woodworkers consider tung oil to be one of the best natural finishes for wood.

Tung oil tree (Aleurites fordii) showing two male flowers and one female flower (left) in which the petals have fallen off exposing the pistil.

Other unsaturated plant oils, such as castor oil and linseed oil, take longer to dry and leave an oily residue until they soak into the wood surface. Tung oil's ability to dry quickly and polymerize into a tough, glossy, waterproof coating has made it especially valuable in paints, varnishes, linoleum, oilcloth and printing inks. The oil-rich seeds are produced inside a thick, woody endocarp layer and are the source of tung oil used on fine furniture.

The word Tung is an ancient Chinese term for heart. Today, the term also refers to the large, dark green, heart shaped leaves of the Tung tree. This is a fast growing, deciduous tree that reaches a height of about forty feet when mature. The life span of a Tung tree is about thirty years. Fruit bearing begins in the third year of tree growth. The Tung fruit occurs in clusters, each of which bear four or five nuts. When the nuts are dried and pressed they yield about twenty percent oil. Under favorable conditions an acre of Tung trees will produce about two tons of nuts and eight hundred pounds (one hundred gallons) of raw Tung Oil annually. Successful cultivation of Tung trees requires exact climatic conditions, including the proper ratio of warm and cool days. The major growing areas include China, Argentina, Paraguay, and parts of Africa.

The first record of Tung Oil appears in the writings of Confucius dated about 400 B.C. . Even then, the Chinese recognized the amazing qualities of Tung Oil. Throughout their history, the Chinese have used Tung Oil to waterproof the masts and sails of junks (boats), to finish furniture of royal families and according to legend, to seal the Great Wall! When Marco Polo returned from China, he brought tales of the wonderful "China Wood Oil". But Tung oil was unable to capture the attention of the West until this century.

TUNG OIL VERSUS OTHER FINISHES

In recent years, those who appreciate the warm richness of beautiful wood have begun to realize what the ancient Chinese knew; when turned into a finishing product, Tung Oil is the finest natural wood finish in existence and has yet to be duplicated synthetically!

Man's ingenuity has created many synthetic finishes, including lacquer, shellac, and varnish all of which protect wood with a hard impervious layer. But these surface finishes prevent the development of patina, the lovely depth and tone that only natural aging can produce. Eventually synthetic finishes will break down and discolor, when that happens the entire surface must be removed by labor intensive stripping and sanding before another coat is applied.

Penetrating finishes formulated with linseed, soy or paraffin oils actually go into the wood and enhance its natural beauty, but these oils often dry incompletely and fail to form a hard and durable surface. Furthermore, they develop a gummy build-up when additional coats are applied. Linseed oil, the most commonly used penetrating finish, darkens and changes color with time and finally disintegrates.

A Tung Oil finish is hard yet flexible, waterproof and impervious to alcohol and many food acids. Tung oil as a penetrating oil allows wood to continue its aging process and to develop its patina. The wood's rich color and grain are enhanced by the natural ambering (coloring) of Tung oil over time. Any sign of wear disappears when a thin "maintenance" coat of oil is rubbed in. The maintenance coats, rather than cause a build-up, actually improve the patina as they protect and preserve the wood. A floor, a piece of furniture, or any other wood object finished and maintained with Tung Oil will never have to be stripped again. The finish will become more beautiful with time.

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Click HERE to see purchase options for Tung Oil.