Why is Heartwood Darker in Color than Sapwood?

To achieve the highest quality of woodworking, it is necessary that you have a sound knowledge of wood and its internal structure. A project can fail solely on the basis of your wrong choice of wood. An area of extreme importance for you in this connection is the link or difference between heartwood and sapwood. Why is it that many carpenters choose heartwood over sapwood? But first, what is heartwood and what is sapwood?

teak wood

Let’s answer them one by one.

Definition: Heartwood is the dead, inner part of the wood of a woody branch or stem which comprises the most part of the cross-section of a stem. It comprises cells that are altered physically and chemically due to the action of mineral deposits. It is also called duramen.

The living part of a tree is sapwood. It transports water, oxygen, nitrogen and minerals. It is also called alburnum.

Location: As a tree grows in years and diameter, an inner part of the sapwood stops functioning over time and eventually dies. This dead part is called the heartwood.

Function: Heartwood provides the tree with structural strength while sapwood transports water right from the roots to the leaves and stores it so that it can give out as much food made in the leaves as required in different seasons. The more a tree is leaf bearing, the greater its volume of sapwood needed.

Appearance: Heartwood is visible by its growth rings, which could be very dark. Sapwood is distinguished by its softer and lighter appearance and its color and texture due to the presence of minerals, gums and resins. As the tree’s diameter increases, the inner layers of sapwood give way to becoming heartwood while on the outside, new layers of sapwood are produced.

Why is heartwood darker in color than sapwood?

Color: Once sapwood has been converted to heartwood, the sap stops flowing in that region and the cells in that area essentially die. In the process organic matter starts filling up the cell walls. So heartwood is usually dark-colored due to the tree’s natural aging process and because of the deposition of organic matter known as extractives, which are responsible for its rich color. However, sapwood is almost always light in color, due to the formation of new wood made with living cells.

Cause of being: Heartwood or duramen is wood that grows due to the presence of naturally found chemical transformation has decayed. It forms spontaneously, and once its formation is complete, it dies. It gets its name only due to its position and not because of any importance to the tree. Sapwood is the living part of the tree that grows on the outside of the tree, in fact all growth of trees begins with its sapwood.

Durability: Heartwood provides the tree with structural strength. It is hard and durable unlike sapwood which is soft and durable.

Water content: Water is present in heartwood in its cells and as free water in cell spaces and cavities. Thoroughly air-dried wood contains about an average of 12% water in its cell walls but nothing in any other form.

However, in the case of sapwood, since it contains the tree’s sap-conducting cells, it has a high moisture content. For a living tree, this is good but not so for woodworkers because sapwood shrinks and moves a lot when dried, therefore becoming increasingly prone to staining due to fungi and decay.

The fact that heartwood contains much less moisture (and is less susceptible to fungus) as compared to sapwood, it is the preferred wood for woodworking projects. Less moisture means that the heartwood shrinks less than the sapwood. Experienced carpenters often remove the sapwood and make furniture out of heartwood.

Resistance to microorganisms: Microorganisms do not easily attack heartwood but sapwood is easy prey for them.

Author: John Clax

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