What is Wood Spalting?

Posted by Christopher Brown on


What is Wood Spalting?

Spalting is the coloring and patterning of wood caused by fungi. Some fungi when consuming wood will produce pigments that will stain and also alter the structure of the wood. This fungal growth creates 3 main types of spalting.


Some wood-rotting fungi produce extracellular pigments that will stain the surrounding wood. There are also fungi that will contain the pigment within their own cells and the staining is created by concentrations of the hyphae (fungal threads) within the wood.

White Rot

The bleaching of wood created when the fungi consume the lignin within the cells; lignin gives the cell walls a darker pigmentation. White rot, when left unchecked, will remove much of the strength from the wood and create what woodworkers refer to as punky, or soft areas.

Zone Lines

Often showing as dark black or brown lines flowing through the interior of the wood. Zone lines are another artifact of fungal growth; when growing and expanding fungi may create these lines as a border wall to protect against other invading fungi.
Zone lines can also serve to wall off a fungus from environmental hazards and secure a resource.

Many beautiful examples of zone line spalting can be found in our wood earring collection.

Zone Lines in maple end-grain.  

What wood can spalt?

All woods technically can spalt, so long as a fungus capable of doing the spalting can gain a foothold and grow. 
Some trees, like the Boxelder (A. negundo) however, create their own characteristic red staining that is not spalting but rather a reaction from the tree itself to internal or external stressors, like physical damage or infection.

Light and dense/closed-grain woods like maple, beech, and birch show some of the best spalting, being pale hardwoods the spalting creates a nice contrast to the natural color of the wood. 

What fungi are doing the spalting?

There is no simple answer to this one. There are many many fungi that decompose wood, some create spalting, some don't, and some do both.

Some species will act as pioneers breaking ground and leaving the wood more hospitable for others to move in. While certain fungi may only stain the wood, others will construct those winding black zone lines. With progressive waves of fungal colonization, the combinations of spalting types can create a beautifully patterned piece of wood.

For example, the ambrosia spalting in the maple log below is created when a small ambrosia beetle bores into the tree, bringing with it a symbiotic fungus that begins to attack the tree. Ambrosia spalting is typically found in the Maple genus of trees -Acer. This type of spalting can be identified by the tiny boreholes in the wood, found within the grey streaks.

Ambrosia Spalting in Maple

What about Mold, can they spalt wood as well?

Indeed molds are fungi, but these species are incapable of decomposing the wood fibers, they will remain on the surface and consume the easy to obtain carbohydrates in the sap and can not spalt the wood.
Green and black molds will typically be found on freshly turned or cut wood that is left in still and moist air. 
Although they can “stain” the wood surface with their spores this is not the kind of staining woodworkers are looking for.
Staining by mold spores can also be unhealthy for the woodworker and or the user of the final product. Spores are the germinating cells or "seeds" of the fungi, and you really don't want to be filling the air of your workshop with a heavy spore load. Spore staining generally does not look good and can quickly ruin a beautiful piece of "green" wood. Although spore staining is not desirable it is usually constrained to the surface and so long as it is not sanded/rubbed or washed into the end-grain can be removed with a little cutting.

Where to find spalted wood.

Spalting is part of the woods decomposition stages, as the breakdown of the wood progresses it becomes less and less usable to woodworkers and crafters. If spalting is allowed to progress for too long the wood will lose all its strength and become punky and soft, enough to be crushed or crumble with your hand.

Finding wood in the wild that is at that perfect stage of spalt without the rot can be difficult. There is however another way. You can spalt wood at home and have more control over the timing and condition of the wood. 
Below are some links to resources showing you how to start the spalting process at home.

Here at Cut Branch, we are always on the lookout for spalted woods, the natural patterns flow beautifully with our many different designs and applications.
Some of our new wood dangle earrings incorporate spalted zone lines, and along with the book-matched grain pattern create a very unique pair.

Finding what looks like a rotten old log and cutting it open to find these amazing natural patterns is something we really enjoy.

For more information on spalted wood and the spalting process check out the links below.

Northern Spalting 

Architectural Digest

Fine Woodworking Articles:

Working With Spalted Wood 
Spalt Your Own Lumber 
Spalt Your Own Lumber: Health problems associated with spalted wood, and debunking myths 




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