Anatomy of Wood

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Anatomy of Wood

Improve your carving efficiency with an understanding of wood grain

by Everett Ellenwood


The way the wood grain lays in a piece of wood will affect every cut you make in every carving you do. The direction of the cut in a piece of wood will determine if you get a clean shiny cut or a cut where it looks like the wood was torn out of the piece.

Understanding the anatomy of a tree will give you a better understanding of the result you will get with each cut. Armed with this knowledge, you can work with the wood, instead of against it, for a more enjoyable carving experience.

Visible Parts of a Tree

The three primary components of a tree are the roots, trunk, and crown.

Roots: Roots are the tree’s anchor and hold the tree erect. They absorb water and minerals from the earth, which are transported through straw-like vessels up through the trunk of the tree to the crown.

Trunk: The trunk, also called the bole, connects the roots to the crown and is usually thought to be the portion without limbs. You can use wood from any part of a tree for carving; however, most carving wood comes from the trunk of the tree.

Crown: The crown consists of the limbs, branches, twigs, and leaves of the tree. Food, called sap, is produced in the leaves through the process of photosynthesis.

Internal Wood Structures

The roots, trunk, and crown are the visible components of a tree, but studying a tree’s internal characteristics gives us a better understanding of the tree’s structure.

Pith: At the very center of the tree is the pith, which is the oldest part of the tree. The pith, together with the tree’s first few annual rings, is called juvenile wood. The pith area has a greater tendency to crack than the rest of the wood in a tree.

Try to avoid carving pieces of wood that include the pith. If you do carve wood containing the pith, design the piece so the pith doesn’t show from the viewing angle.

Annual Rings: Radiating out from the pith are the annual rings. Each ring has two components: early wood (also called spring wood) and late wood (also called summer wood).

Early wood grows at the beginning of the tree’s growing season—the tree’s period of active growth. This wood is made up of large cells with thin walls. As the season progresses, the growth activity slows down and the cells become smaller with thicker walls; this is late wood. Late wood is normally darker than early wood because it has a higher concentration of cellulose. You will normally see one annual ring for each year of the tree’s growth. The rings can vary in width because of weather and other conditions during the growing season.

When a tree is cut into boards or blocks for carving or turning, the beautiful figure you see is created by the annual rings.

Cambium Layer: The cambium layer is located between the bark and the wood. This is where cell division takes place, and when the cells divide, they become either wood cells or bark cells.

If a tree is cut in the spring or summer, when active cell division is taking place, you’ll feel a slippery, slimy area just under the bark—this is the cambium layer. During this active growth period, the bark and wood are loosely bonded together, so when the wood is dried, there is a very good chance the bark will fall off. During the fall or winter, when there is very limited cell division taking place, the wood and bark will be tightly bonded together. If you want to create a
carving where the bark remains intact
on the wood, the tree must be harvested in the fall or winter.

Bark: The bark is the tree’s protective covering—its skin. Bark is made up of living and dead cells, which keep moisture and gases contained in the tree. Bark also helps the tree resist attacks by insects and micro-organisms and protects the tree from damaging weather conditions.

Heartwood and Sapwood: As a tree grows, there comes a time when the entire trunk of the tree is not required to supply water to the leaves. When this occurs, the vessels in the center of the tree fill with extractives, minerals, and tannins. This filled area then becomes what is known as heartwood.

The heartwood of walnut is darker than the sapwood, but basswood is a consistent color.

The heartwood no longer conducts water, but, being filled with extractives and minerals gives strength to the tree. It becomes the tree’s vertebrae. The area which is still conducting water to the leaves is known as sapwood. As the tree grows in diameter, with the addition of new sapwood each year, the heartwood area will also expand because each tree only requires a certain number of sapwood rings to supply water to the leaves. The number of sapwood rings will vary from one tree species to another. Catalpa trees only require a couple of sapwood rings, where walnut trees will have 10 to 20 sapwood rings.

Differentiation in color between sapwood and heartwood also varies between species of trees. In some species of trees, like walnut, you will see a very distinct differentiation in color between heartwood and sapwood. Trees like basswood and butternut have very little differentiation in color between the heartwood and sapwood. Most carvings will be done using the heartwood.

Horizontal vascular rays connect the vertical vessels together. These rays are clearly visible in this piece of oak.

Vessels and Rays: Looking at the cross-section of a hardwood tree under a microscope is like looking into the end of a large bundle of straws.

These straws are the vessels which run vertically through the tree and carry water and minerals from the roots through the trunk and out to the leaves. In the leaves, through the process of photosynthesis, food (which is known as sap) is manufactured for the growth and sustenance of the tree. The sap is transported back down the tree through cells just beneath the bark (the phloem) and is distributed through the tree horizontally through vascular rays. The vascular rays are weak thin-walled cells that weave in between and around the vertical vessels.

In most wood types, these rays are only visible when magnified. The rays bond the vertical vessels to one another, but are not nearly as strong as the walls of the vessels. If a wedge-shaped object, like a knife or gouge, goes between the vessels, the ray cells tear and the vessels split from one another. This is called splitting with the grain.

It is important to be aware of how the vessels will tear apart from one another because it will affect every cut a carver makes. Your objective should be to make each cut across the vessels, giving you control of the cut. Never give the carving tools the opportunity to go between the vessels, causing them to split from one another.

When a knife is allowed to wedge between the vessels, the vascular rays tear, and the vessels split from one another.

Putting the Knowledge to Use

Every carving contains transition points where you need to change the direction of your cut. A negative transition point is the area you must cut toward. A positive transition point is the area you must cut away from. You must cut in the proper direction so the tool will not go between the vessels.

If you cut in the wrong direction, the wood will tend to split. I can’t impress on you enough the importance of learning how to cut wood so your carving tools never go between the vessels in the wood. If you can’t vividly see the direction of the grain in a piece of wood, lightly push the tool into the wood. If the tool wants to go between the vessels (the grain of the wood), you’re cutting in the wrong direction. To get a clean cut, you need to make the cut from the other direction.

The best way to learn is by doing. This simple exercise demonstrates how to work with the wood grain and negative and positive transition points. Always cut away from a positive transition point and toward a negative transition point.

Vertical straw-like vessels carry water and minerals from the roots to the leaves of the tree. These vessels affect the way a knife cuts through wood.

Every cut you make should have a specific purpose. If you don’t know what you want to accomplish with a specific cut, don’t make it. Take time and learn with each cut you make. The more you know about wood, the more effectively you can use it, and the more enjoyment you will get from carving.

Working With Wood Grain

1. Cut the teaching blank. The shape is not extremely important, but it should look similar to the photo. Mark the grain direction and transition points. The center dip is the negative transition point, and the right and left bumps are positive transition points. The arrow running laterally marks the direction of the grain.

2. Cut away from a positive transition point. You will be cutting across the exposed ends of the vessels and you’ll get a clean controlled cut.

3. Cut toward a positive transition point. You are cutting into the exposed ends of the vessels. The knife will attempt to take the path of least resistance. When this happens, you’ve lost control of the cut and the wood will tend to split.

4. Cut toward the negative transition point. Cutting in this direction produces a clean controlled cut. If you cut beyond the negative transition point, you risk splitting the wood.

5. Cut from the other direction toward the negative transition point. Cut from the other direction, meeting the first cut, so the waste wood will come out cleanly.

6. Cut beyond the negative transition point. As with the cut made toward the positive transition point, the tool will attempt to take the path of least resistance and go between the vessels, causing the wood to split. Any time you allow the tool to go between the vessels (the grain of the wood), you loose control of the cut.

About the Author

Everett Ellenwood is a well-known carving instructor and author. He also produced DVDs on carving and sharpening.





This article was first published in Woodcarving Illustrated Spring 2009 (issue 46).





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Read more about woodcarving in The Complete Book of Woodcarving by Everett Ellenwood.

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