I'm constantly looking for burls and figured wood to use for making handles for the woodcarving knives that I sell. In looking for burl I did a little research to answer questions from my customers about what burl is.
You have no doubt seen Burl used in furniture manufacturing in the form of veneers, paneling, pen turnings, pool cues and of course, knife handles. If you drive a Mercedes or say a Jaguar, you probably have burl on your dash. I looked at my Old Ford F-150 and alas, no burlwood accents.
Burl is a fast growing growth found on some trees that is filled with small knots from dormant buds. This gives the grain small "eyes" that give burlwood its desirable figure. White Paper Birch has on occasion, a different figure in its burl in that it gives a flame figure with no eyes. This has a prismatic effect that gives the appearance similar to gazing into a swimming pool. Usually a burl appears as a result of some stress from damage caused by a fungus or insect. Not many trees create burls but when they do they usually can be found in groups. The reason for this is that if the fungus or insect is present in one tree it usually affects the trees around it. Usually the tree can develop a burl but still be healthy and live on for many years. If a burl develops too large it can cause stress on the tree and cause it to die.
Not all burlwood is found above ground. Some of the best burlwood is found in the rootball. When a tree grows it sends out roots to a wide area to get water in nutrients. This seems to happen in a nearly chaotic way causing stunted roots and root buds creating a sort of underground burl. I have found that in White Paper Birch roots that the more trunks attached to the same root creates a better root burl. So, the next time you have to take out that prized elderly birch, Pincherry or Black Cherry tree, try and dig the stump out for some really neat wood underneath.
Just about any tree found in northern Minnesota has the ability to create burls. I have gotten most burls from Black ash, Sugar Maple, and White Paper Birch. Burl can also be found in coniferous (Pine) trees. I have had some Cherry Burl which is awesome to work with because of the smell it produces and the tiniest eyes and grain structure that I have seen. Hickory burl is unbelievably hard and very difficult to work with.
Removing a burl from a tree can risk the health of the tree. The burl may have started growth early in the trees life and is grown into and around the heartwood or completely around the sapwood. Removing the burl may result in ringing the tree, cutting off its nutrient path and killing it. So should you decide to take one off a tree be careful and aware that it may kill the tree.
Burlwood can be difficult to work with because of its swirling grain, eyes, and inconsistencies in hardness. Even with the sharpest of gouges and chisels, carving can be difficult due to tearout. The most effective way to work with burl is to use power carving burs and low grit sanding drums. These methods use a smaller cutting edge, but create a lot of dust, so a dust collection system is almost mandatory. Remember that some burls are as a result of fungus, so when carving these burls you are making these fungi airborne and breathable, possibly causing an allergic reaction.
Some of the largest burls are in Australia and can be as big as a small truck. The redwoods of Northern California redwoods (Sequoia sempervirens) produce gigantic burls used to carve single pieces of furniture from one burl. I purchased a White Paper Birch Burl that filled the back of my full-sized pickup and is the primary suspect in a broken leaf spring that was found later.
I will continue looking for burls and burl information. So there you go, that's what I know about Burls.