Understanding the Distinctive Markings of Oak

Click on the images below to see some of the main characteristics discussed in the article.

Medullary RaysSapwoodKnotsCracksPinholeCats Paw

Distinctive markings

Medullary rays

Medullary rays are pale in colour and can appear as stripes, waves or flecks against the grain. They can appear to have a shine to them and will often gleam under direct sunlight. Medullary rays are a natural occurrence in timber and their presence is an indication that your flooring has been crafted from quality quarter sawn oak.

Why do they occur? Before a tree is sawn, it has a network of vein-like cells inside it that transport nutrients from the heart of the tree to the extremities. When the tree is milled, certain cuts (usually those made to the top and bottom of the log) run across the tree's vein-like cell structure at an angle resulting in these unique, vein-like markings known as medullary rays. Medullary rays are also known as Oak figure, mirrors and tiger stripe.


Some boards can have a distinctive lighter coloured streak running through them - this is known as sapwood. Sapwood is not a defect but rather a natural occurrence in timber - it is the younger wood of the tree that grows around the older darker centre of the tree (the heartwood) and darkens as the tree grows. Sapwood in a floor will become more prominent over time with exposure to Sunlight/UV. The higher the grade of your flooring the less sapwood it should have. Again, if you do not like sapwood you can ask your installer to leave aside any boards with distinctive sapwood.

Staining the boards can lessen the appearance of sapwood, but does not entirely hide this natural characteristic. A stain helps to blend the natural characteristics together but does not eliminate them. Roasted or fumed timber has very distinctive sapwood as the heating process causes even greater colour contrast making the sapwood even more prominent, especially over time.


Knots are unique circular or oval-shaped markings, usually with a darker coloured centre. They can vary widely in size and occur naturally in wood where a branch grows out of the main trunk and can extend deep into the tree's core. In terms of timber flooring, there are two types of knots - dead knots and live knots. A dead knot is where the core has fallen out or been removed, and will usually be filled. With a live knot, the core is intact and does not require filling. Knots give special character to timber flooring and no two knots look the same. The grade of flooring you choose will affect the size and frequency of knots found in your flooring.

Cracks (aka shakes)

Shakes are naturally-occurring cracks in timber. There are many different causes for shake, for example frost, high winds, rapid or uneven drying, and trees being felled past maturity. These cracks are usually filled but in some cases may be part-filled as part of a floor's feature. The number and size of the shakes in your flooring is again affected by the grade you choose.


Pinhole is usually seen in a series of tiny black holes, caused by pinhole borer and common in timber flooring. The borer cannot survive in timber once it has dried out so they are usually long gone by the time the timber flooring is being laid. Boards with pinhole can usually be found in any grade below prime.

Cats paw

Cats paw is seen as a cluster of small pin knots surrounded in lighter coloured swirls, which has been known to look like a cats paw. Cats paw figuring is highly prized by wood lovers and is usually the result of a deformation in the tree such as a burr (see above).

What is Figuring?
Figuring refers to the markings found on longitudinal surfaces of timber. The figure of a piece of wood can
be linked to factors such as its grain and the way it was cut or it may be due to the unique properties of the timber. Types of figure include 'cats paw'/'bears paw'/bear scratches', pinhole, cats paw, swirl and more.

Figuring can often occur as a result of a tree having a burr. A burr (or burl) is a tree growth where the grain has grown in a deformed manner. It is caused by stress on the tree and is commonly seen as a growth on the side of a tree which can extent far into the trunk. Burrs contain very unusual wood that is highly figured and very sought-after, especially by the woodworking industry.

Date Added: Thursday, 14th September 2017