In short, pith rays are growth cells that typically grow in oak, and which run radially from the center of the trunk (the pith) and vertically outwards towards the bark side.
They are characterized by their bright and patterned appearance, which is particularly evident after the oak has been sanded and oiled.
The medullary rays are actually 'growth rings' in the form of plant cells that grow with the tree, and they have a changing color that appears a bit silvery depending on which direction you look at them.
In addition to oak, pith rays are also found in conifers and hardwoods, but it is in oak that they are most characteristic.
Why do you see pith rays in oak?
The reason they are visible in many oak products is because of the way the wood is cut.
Image from thefurnituremarket.co.uk
There are basically two ways to cut oak:
- Planar cut
- Quarter cut
Quarter-cut means that you divide the trunk into 4 quarters - like a layer cake. Then you cut slices of the wood across the quarter of the trunk. The slices will therefore not be as wide, and the process itself is somewhat more time-consuming than when cutting flat.
At the same time, the direction of the grain rings means that quarter-cut wood will typically have more pith rays in the surface and be more durable than plane-cut wood.
Are spinal cord rays a sign of disease?
No - on the contrary. The pith rays are the nerve of the tree's growth, and according to the above regarding quarter cutting, it is a sign of healthy and more durable wood that has required a lengthy process to cut out.
The pith rays are therefore completely natural and a sign that your oak products are made of quality wood. At the same time, the pith rays give the oak a characteristic and unique expression that you will not find in the same way in other wood products.