burl

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A burr on a silver birch at Corsehillmuir Wood, Kilwinning, North Ayrshire, Scotland.

A burl (British bur or burr) is a tree growth in which the grain has grown in a deformed manner. It is commonly found in the form of a rounded outgrowth on a tree trunk or branch that is filled with small knots from dormant buds. A burl results from a tree undergoing some form of stress. It may be environmental or introduced by humans. Most burls grow beneath the ground, attached to the roots as a type of malignancy that is generally not discovered until the tree dies or falls over. Such burls sometimes appear as groups of bulbous protrusions connected by a system of rope-like roots. Almost all burl wood is covered by bark, even if it is underground. Insect infestation and certain types of mold infestation are the most common causes of this condition.

In some tree species, burls can grow to great size. Some of the largest occur in redwoods (Sequoia sempervirens); when moisture is present, these burls can grow new redwood trees. The world's largest and second-largest burls can be found in Port McNeill, British Columbia. One of the largest burls known was found around 1984 in the small town of Tamworth, Australia. It stands 6.4 ft tall, with an odd shape resembling a trombone. In January 2009, this burl was controversially removed from its original location, and relocated to a public school in the central New South Wales township of Dubbo.

Burls yield a very peculiar and highly figured wood, one prized for its beauty by many; its rarity also adds to its expense. It is sought after by people such as furniture makers, artists, and wood sculptors. There are a number of well-known types of burls (each from a particular species); these are highly valued and used as veneers in furniture, inlay in doors, picture frames, household objects, automobile interior paneling and trim, and woodturning. The famous birdseye maple superficially resembles the wood of a burl but is something else entirely. Burl wood is very hard to work in a lathe or with hand tools because its grain is misshapen and not straight.

Some burls are more highly prized than others, including ones originating in rural areas in central Massachusetts, northeast Connecticut, and as far south as Philadelphia. Some types display an explosion of sorts which causes the grain to grow erratically, and it is these burls that the artist prizes over all other types. These spectacular patterns enhance the beauty of wood sculptures, furniture, and other artistic productions. Burls are harvested by a variety of methods.

Redwood Tree Burls

Many redwood trees have burls but they are not often harvested for use. There are two things that hinder the harvest of redwood burls, the first being that removing a burl can cause the death of the tree. The second is the sometimes tremendous size of redwood burls; removing them can require the use of heavy equipment, which can be expensive and difficult to get to the tree's location.

Amboyna Burl

There are many types of burls, some common and inexpensive, others rare and very expensive. An example is maple burl (cheap) versus amboyna burl (expensive). The amboyna burl comes from the Asian paduk tree. Paduk is quite common while the burl is extremely rare. The amboyna is usually a deep red, although the more rare moudui burl is the same species but the color is from golden yellow to yellow-orange. The sap wood is creamy white with brown streaks. The common use for amboyna is interiors for luxury cars, turnery, cabinets, veneer, and furniture. It grows in south-eastern Asia, and costs from $18.00 b/f to $22.00 b/f.

Gallery

Maple burl, not to be confused with bird's-eye maple	A bowl made from a plum tree burl	A giant burl near Solduc Falls in Olympic National Park	A large spruce burl on display at the University of Alberta
A longitudinal section through a Larch bur from Ayrshire, Scotland	A bur on a Larch (Larix decidua), Ayrshire, Scotland	A burl the size of a refrigerator on the trunk of a Coast Redwood	burs on the bark of an old apple tree
Oak burl with a wheelbarrow for perspective Wellfleet, Massachusetts	A tree with many burls in Olympic National Park

References

• Corbett, S. (2006). The Illustrated Professional Woodworker, London: Anness Publishing.