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
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
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.
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.
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.
Putting the knowledge to use
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.