Some Wood Terms: ever wonder what it means when you see wood descriptors such as Bird’s Eye, Fiddleback, Curly, Crotch, Quilted, Spalted, Wormy?
A few woods, most notably maple but also anigre and a few others, can exist with large numbers of small round “defects” that do indeed resemble the eyes of birds. The density of the eyes ranges from sparse to dense, and the definition of “dense” frequently depends on the greed and honesty of a seller, so this is not a good figure to buy sight unseen. A good, truly dense, bird’s eye maple board can make a spectacular addition to a project; it is very popular for jewelry boxes.
When cut into veneers, the logs are most often rotary cut or half-round sliced (in an arc) to produce the most uniform distribution of nice round eyes.
There are a few woods that are sold as “bird’s eye” with a density of eye figure so low as to make the term a joke. Zebrawood in particular comes to mind for his. I have seen zebrawood veneer sheets that re sold as “bird’s eye” due to having literally 8 to 10 eyes in an area of 5 or 6 square feet.
A burl is a wartlike, deformed growth on the trunk or root and sometimes even the branches of a tree, caused by (1) an injury to, or (2) and infection in, the tree just under the bark, or (3) the existence of an unformed bud which has all the genetic material necessary to grow a full branch, or even a whole tree, but which for some reason did not grow properly. In any case, the result is that the tree cells divide and grow excessively and unevenly in a process somewhat analogous to cancer cells in a mammal. Burls are sometimes called tumors on wood, although I’m not aware of their ever being fatal. Trees with burls continue to grow otherwise normally.
Continued growth follows the contour of the original deformity, producing all manner of twists, swirls and knots in the wood fiber. Usually, this results in wood that has a spectacular pattern that can be used to great effect in woodworking, and sometimes it is also accompanied by the creation in the burl of dormant buds which create “eyes” that make the burl even more spectacular when worked.
Burl wood is usually darker than the rest of the tree and in some cases (Paela comes to mind) may be a significantly different color altogether. Because of the diverse grain direction, burl wood cannot be relied on for strength, but that’s of little consequence since burls are prized for beauty, not strength.
Burl wood can be difficult to dry without cracking. Sometimes there are bark inclusions in burls, and also sometimes gum pockets, either of which can cause surface defects when the burl is worked. In some species of wood, gum pockets are common in any burl found on the tree.
Burls come in all sizes and shapes from golf-ball and smaller to hundreds of pounds of massive growth on the side of a large tree. Burls as large as 4 feet by 8 feet have been reported as have trees with hundreds of small burls. On really large trees, such as the redwood, burls commonly exist that are large enough to be used to create veneer. Burl veneer frequently does not stay flat after cutting and has to be moistened and clamped flat before and/or during application.
“Cat’s Paw” and “cluster burl” are a couple of commonly identified types of burl figure. Cat’s paw is frequently found in cherry and cluster burls are found in a number of species. Most often, burls have no sub-designation and occur in a large number of species. Common burl species include redwood, oak, ash, maple, madrone, elm and walnut. Some exotics with very popular burls are mappa (poplar burl), thuya and imbuya, and there are MANY more.
Compression wood is a portion of a tree where the wood fibers have been compressed due to stress in the tree. This can be caused by irregular growth such as a tree that grows on a riverbank and then tilts as the bank slides into the water, causing the tree to have compressed wood in the side next to the water because the tree is bent over in that direction.
Crotches are an extreme form of compression wood. They are caused by the forces exerted within the tree to support a main branch where it joins the trunk, and of course the bigger the branch, the more the compression. The compression decreases as one moves away from the point where the branch meets the trunk, so crotch wood frequently exhibits an extreme degree of grain variation. The compression process that strengthens the tree so it can support the branch causes the wood fibers to twist and compress, creating various figures and grains that can be very beautiful. Unlike burls, crotches have grain that, while quite distorted, is basically the same grain as the other wood in the tree and does not tend to the extreme swirls and eyes of burl wood, but even so, crotch wood can be wonderful to behold.
Crotch wood is typically harder and more dense than a straightgrained portion of the same tree. Depending on the appearance, a crotch may be called a “flame crotch” or a “feather crotch” (and less frequently as “plume”, “roostertail” or “burning bush”) and frequently the crotch area is somewhat symmetrical on both sides of the branch so that a crotch piece cut parallel to the bole of the tree will produce a look similar to that of book matching.
Contortions in grain direction sometimes reflect light differently as one moves down the grain and this creates an appearance of undulating waves known as curly grain. It is frequently described as looking like a wheat field in a mild wind, and can be so strong an effect that your eyes will swear that a flat piece of wood has a wavy surface. Many species develop this figure, maple being a very common example. Stump and butt sections of trees often produce a diagonal, staircase-like curl referred to as “angel steps”, and a rolling curl figure that is called “cross-fire”. An extreme form of curly figure is called “fiddleback”.
Curly figure in wood (and fiddleback is just a variation of curly) is caused by contortions in grain direction such that light is reflected differently at different portions of the grain, creating an appearance of undulating waves, also called a “washboard” effect because it looks like an old corrugated-steel washboard. “Fiddleback” figure is a form of curly figure where the curls are very tight and fairly uniform, generally running perpendicular to the grain and across the entire width of a board. The name comes from the fact that such wood became popular to use on the backs of violins (fiddles), and nowadays guitars, because the figure is frequently very lively and attractive and such wood generally has good resonance properties. Logs for fiddleback veneers are quartersawn to produce very straight grain with curls running perpendicular to the grain and uninterrupted from edge to edge of the sheet.
Some reports claim that a tree which buttresses itself against north winds will have compressed annular growth rings in the area facing north and expanded rings facing south and that the stress in the compressed rings is believed to cause the fiddle back figure. I have no idea whether this is true.
Many species develop this figure, but the most common ones are maple, makore, anigre, and “English Sycamore” (which is actually a form of maple). Some of the prettiest versions occur in claro walnut and koa. There are woods (laurel comes to mind) that have a figure that is technically a true fiddleback figure, but which is so light as to be almost indiscernable, and there are others that have fiddleback figure that only runs for a few inches of width in a plank although it may run the full length. Also, plain curly is sometimes mislabled fiddleback and true fiddleback is sometimes labled as just curly, depending on the whims of the vendor.
Pomelle is a type of wood figure that resembles a puddle surface during a light rain: a dense pattern of small rings enveloping one another. Some say this has a “suede” or “furry” look. It’s usually found in extremely large trees of African species like sapele, bubinga and makore. Some domestic species with a sparser, larger figure are referred to as “blistered”. The term is not used totally reliably and you may encounter some confusion among the terms “blistered”, “pomelle”, and “quilted” from different vendors. The name Pomelle comes from the French word for “quilted”, so it’s not too surprising to find this confusion. You may see “pomelle pebble”, “pomelle swirl”, “pomelle quilted” and other combination terms that are not necessarily used consistently among vendors.
Spelling variations include “pommele”, “pommelle”, “pomelle”, and “pomele”
Quilted figure somewhat resembles a larger and exaggerated version of pommele or blister figure but has bulges that are elongated and closely crowded. Quilted grain looks three-dimensional when seen at its billowy best. Most commonly found in maple, it also occurs in mahogany, moabi, myrtle, and sapele, and less often in other species.
Spalting is a dark vein caused by a pattern of bacterial rot in dead wood that once stabalized often looks like a black ink line of varying thickness and great irregularity drawn through the wood. When it is very sharply defined black lines it is sometimes called “black-line spalting” — in some trees, oak for example, spalting is never black-line and in fact can be VERY vague, amorphous, blotchy black or dark-gray areas. In some woods, spalting causes some color changes other than black. I’ve seen some spalted woods that are very colorful.
Spalting can be encouraged by keeping a dead tree moist. Spalting is a form of decay and if spalted wood isn’t stabilized at the right time, it will just rot. I need to do more research on this, but at present, my impression is that spalting is something that mostly happens only in softer woods. Wood that is really heavily spalted and still completely solid is rare, since advanced spalting is generally accompanied by enough decay to soften at least some areas of the wood.
A form of “defect” or “character” (depending on how you look at it) in wood where there are numerous elongated “spots” throughout the wood where it has been eaten away by various boring agents (generally beetles). Sometimes the eaten away area is filled in by some kind of natural process so that there are no voids but just discolored areas. This is usually in the form of elongated worm-shaped areas, but may also occur as spots depending on the cut of the wood and other factors. NOTE: worm holes are quite common in wood and the presence of a few worm holes does not generally trigger the designation “wormy” which, as I said at the beginning of this paragraph, is usually reserved for wood with NUMEROUS worm holes. In many trees, wormholes are far more likely in the sapwood than in the heartwood.
Excerpted from http://www.hobbithouseinc.com/personal/woodpics/