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Medullary Rays in Oak Stairs

Oak stair

Oak is a popular hardwood species known for its durability, strength, and distinctive grain patterns. Some think this is a defect in oak but it is actually one of the features that make oak unique - medullary rays, which are thin, radial structures that run perpendicular to the growth rings in the wood. These rays are responsible for many of the visual characteristics that make oak such a sought-after material for furniture, flooring, and stairs.

What are Medullary Rays?

Medullary rays, also known as pith rays, are thin, ribbon-like structures that run vertically through the wood, perpendicular to the growth rings. These structures are made up of cells that radiate outward from the pith or center of the tree. Medullary rays can vary in size and shape, depending on the species of tree and other factors.

Why are Medullary Rays Important?

Medullary rays play an important role in the growth and development of trees. They transport nutrients and water between the cambium layer (the layer of cells responsible for growth) and the center of the tree. Medullary rays also help to stabilize the tree, distributing stress and supporting the growth of new cells.

In addition to their biological functions, medullary rays also have important aesthetic qualities. In many hardwood species, the medullary rays are visible on the surface of the wood and create unique patterns and textures. This is especially true in oak, where the medullary rays can create striking designs and figures.

Oak is known for its distinctive grain patterns, which are created by the combination of the growth rings and the medullary rays. In oak, the medullary rays are often larger and more prominent than in other hardwoods, creating a unique and recognizable pattern.

When oak is quarter-sawn (cutting the log perpendicular to the growth rings), the medullary rays are especially pronounced, creating a beautiful and highly sought-after effect known as "ray fleck." Ray fleck appears as a shimmering, iridescent pattern on the surface of the wood and is highly valued for its beauty and rarity.

oak stair

The presence of medullary rays in your staircase is not a sign of damage or flaws. In fact, it indicates that your stairs have been crafted from the finest and most expensive quarter sawn oak. When it comes to logging and carpentry, oak trees can be sawn in two ways: tangential or plain sawing, which yields the most timber from the trunk and is faster and less wasteful, and quarter sawing, which is slower, produces less board footage, and is more expensive. However, quarter sawn timber is much stronger due to the ring growth direction and displays more medullary rays on its surface.


Medullary rays are an important and fascinating feature of oak and many other hardwood species. They play a vital biological role in the growth and development of trees, and also create beautiful and unique patterns and textures in the wood. If you're considering using oak in your next woodworking project, be sure to take advantage of the medullary rays to create a stunning and distinctive design.


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