Spalt or spalting is probably the most exciting characteristic and beautiful visual effect you can find in any wood bowl blank.
When people hear the word “spalt” for the first time, they often turn their heads to the side a bit and ask, “what did you say?”
What is Spalting?
Spalting is somewhat graphic or colorful markings composted of mineral deposits left by fungi found in aged or decaying wood.
Spalt markings inside wood are evidence of the presence of fungi that has moved through and consumed sugars within the wood fibers.
In this article, we will explore:
- What is spalting
- The history of spalted wood
- Different types of spalt
- Finding spalted wood
- How to make your own spalted wood
- Myths About Spalt
- Adverse Effects of Turning Spalted Wood
- Is Spalt Dangerous?
- Age and Usefulness of Spalted Wood
- How to best turn spalted wood
What Spalting is Not
Spalting is not a mold or other undesired “growth.”
Colors that appear in wood, especially right after a living tree has been cut, are not usually spalt.
Naturally appearing colors in the wood are, in most cases, the tree converting sugar into a defensive substance to fight disease and predators to prevent injury.
Tree defenses can be as simple as offensive smells to divert interested parties, all the way up to toxins designed to disable invaders.
Some of these defenses show up as colors or streaks in the wood grain.
The pink, red color of Box Elder wood, for example, is not spalting. Also, most trees produced colorations fade over time, including the pink of box elder.
The tree produced colorations are typically water-based and will dissolve or fade over time.
Because spalt is comprised of minerals manipulated and moved around by fungi, and not water-based, spalt is one of the longest-lasting colorations found in wood.
Black zone lines and other colored spalting rarely fade or change over time.
Battle Black Zone Lines
The most graphic of all spalt is the black zone line spalting.
Black zone line spalt looks like a fine-tip ink pen has been used to cover the wood with wandering lines of graffiti.
At first glance, it’s easy to think of the black zone line as the path or trail of the fungus. However, this is not believed to be the case.
A black zone line is the confrontational meeting point or boundary between two different types of fungus.
If we could see through a microscope at a cellular level, masses of fungus blobs move forward and butt heads with other different blobs of fungus. Where they meet a black line, kind of like a fence or border is formed.
Understanding Spalt and Fungus Better
Spalt is only part of fungus’ very elaborate role in the complete life-cycle of trees.
When a tree falls or stops growing, the fungus enters the cells of the wood and consumes sugars and other elements to ensure the fungus survival and start the decaying process of the tree.
But the fungus is not just there to “eat” the tree.
Fungi works symbiotically throughout the entire life of the tree.
Much like bacteria and microorganisms live on us by the trillions in a delicate happy, balanced harmony that helps keep us alive, well, until there is an imbalance.
We are only just now starting to understand the enormous role fungus plays in sustaining, possibly the entire world. I know that might sound extreme, but it is true.
Most of us think of the iconic wide-brimmed mushroom as the limit of fungus.
But, what we see in each mushroom on the ground level perhaps only represents an infinitely small proportion of the total fungal network, probably in the neighborhood of less than one-trillionth.
If you get a chance to read The Hidden Life of Trees by Peter Wohlleben you will discover some fantastic insights.
Did you know trees do not process minerals on their own? And without a vast mineral-processing fungal network within a tree’s root system, or possibly within the entire tree, trees would only be able to grow a few feet tall and then flop over like blades of grass.
If you are even mildly interested in trees, read The Hidden Life of Trees, and it will blow you away.
Is Decaying Wood Good To Turn?
I can hear what you’re thinking. I thought the same thing at first.
“Wait, do I want to turn decaying wood? Won’t it just rot away?”
Here’s the cool thing. By turning a bowl from spalted wood, you stop the decaying process.
Exposing the wood to oxygen stops the whole breakdown process and freezes the fungus in its tracks.
Many times, the fungus has already “left the building,” or log, long before you decide to turn it.
Different Types of Spalting
There are many different types of spalting around the world.
The most common spalting to find in North America is black zone spalt and white rot spalt. Other spalts are not as common as black zone and white rot.
Black zone spalting is easily noticed and very graphic. Black zone spalt can change a boring monotone piece of wood into a tapestry of beautiful interlocking line art.
White rot spalting can appear distinct on some types of wood and be almost invisible on others. White rot spalt isn’t as bold as black line spalt.
Beyond the black zone and white rot spalting, there are numerous different colors and patterns of spalt created by various types of fungi.
South American spalting is off the chart with all kinds of colors and patterns that can appear almost surreal.
History of Spalt and Spalting
Spalted wood has been used for centuries around the world by craftsmen and woodworkers.
During the Renaissance, wood with spalted features was used to make veneers that were applied to furniture, cabinetry, and even cut into individual shapes to create elaborate murals.
Spalting in North American craftsmanship was pretty much a lost art until the late 1960s when Melvin and Mark Lindquist began using spalted wood to produce amazing turned projects.
David Ellsworth discovered the technique of spalting as well in the 1970s and began incorporating spalted wood in his icon hollow forms.
Finding Spalted Wood
So, enough talk about what spalting is and its history, let’s get our hands on some spalted wood.
How do I find spalted wood?
Great question. Downed trees or logs that have been left untouched for usually at least a few months may have spalt inside.
Look at the end-grain of a log for lines or splotches that look like stains. You may need to cut off a clean area at the end of a log to see better.
Another great way to find spalting is to look for fungus or mushrooms sticking out of the wood.
After the fungi consume the sugars in the tree, it “fruits” in the form of mushrooms.
Think of mushrooms as spore vehicles or a fungi transport system.
If you want to make your spalt, which we will cover next, keep an eye out for mushrooms or fungus attached to downed wood.
The best way to get your own local spalt-producing fungus is to go for a walk in the woods.
Look for downed trees with mushrooms on the outside and collect a few in a plastic zip-lock baggie.
Be careful while collecting because some mushrooms and fungi can be harmful.
I’m not pretending to know everything about mushrooms in this article. So, use caution and don’t consume wild mushrooms without proper knowledge nor inhale spores when collecting.
Protective gloves, while handling the mushrooms, are a good idea.
A great simple and common fungus to look for is “Turkeytail.”
I have had great luck using Turkeytail mushroom to produce spalt.
How to Grow or Encourage Spalt the Easy Way
You basically need two things to encourage the production of spalt in cut wood.
Moisture and the presence of fungi are critical to forming spalt.
I must say I’m very blessed to live in a location that has plenty of rain and humidity, as well as year-round warmth. Spalt promotion for me is effortless, I just have to wait a little while. 😉
I’m going to share what works for me. You may need to take additional steps, which we will cover shortly.
To encourage spalt growth, I cut round logs longer than I need for bowl blanks and stand them on end on the ground.
I believe that contact with the ground is beneficial, but this may not be necessary. The fungus may already be in the wood and not introduced via the ground contact.
An alternative possibility is the moisture coming from the ground may also help the spalting process.
Once the wood is outside and in the elements, I wait.
Like everything else in woodworking, every tree species is different. But, usually, between three to six months, spalting will begin to appear.
If you live in a dry clime, you will need to make sure your woodpile stays moist continually.
The breathable canvas cloth is better than a plastic cover that can promote mold growth. Also, if you use a plastic tote, make holes in the lid, or loosely attach the lid, so it too can breathe.
Contained wood will probably need to have fungus introduced before spalt will develop.
Collect local mushrooms from rotted logs or leave a few logs out back in the weather. Eventually, you will probably find spalt inside these exposed logs.
Introduce a few crushed up mushrooms or even a few cut off pieces of collected spalted logs to your new fresh pile and make sure it stays moist.
Advanced Ways to Grow Spalt
If you want to get technical and create different specific types on spalting, I suggest getting Sara Robinson’s Spalted Wood book.
Sara details exact scientific ways of controlling spalt, usually in small batches of contained wood samples.
While I admire Sara’s dedication, I just want to turn wood bowls. The level of attention to detail needed to create some of the spalts she describes is overwhelming to me.
But if you want to try to create a pink or turquoise spalt, she has the answers and even the spalting specimens for sale.
Myths About Spalt
If you dig around online about spalting, there are many myths.
The biggest myth about spalting is you need to feed it to make it grow. This is NOT true!
Actually, feeding spalt will usually have the opposite effect and not promote spalt growth.
Many people claim you need to add yeast, food scraps, or pour a beer over the wood to get the spalt to form. Not the case.
Adding “food” for spalt defeats the whole natural fungi-cycle.
When a tree dies, the symbiotic balance between the tree and the fungi stops. At that point, fungi begin to consume the sugars in the wood.
If new “foods” such as yeast or beer are added, the fungi will consume those instead of the natural sugars in the wood.
Another myth about spalt is peeing on the wood.
Yeah, that’s not true either.
Peeing on the wood is kinda funny, but it does nothing to aid the spalting process, except perhaps adding moisture. LOL
Randomness and Location of Spalt
Spalt forms randomly inside a piece of wood based on many conditions.
Every species of tree is different and can appear different when spalt is present. Some tree species show spalt from the pith to the bark, while others may only have spalt in the outer sapwood.
When turning wood that only has spalt in one area or another is can be beneficial to orient your bowl blank to best showcase the spalt.
If you have a log with spalt only in the sapwood, it might be best to orient a bowl with the rim located along the cut log half.
However, if the spalting appears throughout the bowl blank, especially near the pith, a natural edge bowl can then highlight that spalt in the base of the bowl.
Age and Usefulness of Spalted Wood
In general, once a piece of wood has a desired amount of spalt, turn the wood as soon as possible.
If a spalted log is left for an extended period, all the other decaying forces will work to thoroughly break down the wood fibers until the piece is useless for turning.
It is best to process a large pile of spalted wood into turned and round bowl blanks to open the wood, which presents oxygen and stops the rot.
Once the majority of the bowl blank has been cut and shaped, the spalting and rotting process with slow dramatically.
When a bowl is rough turned or final turned with wood finish, the decaying process, if not too far along, will come to a complete stop.
Adverse Effects of Turning Spalted Wood
Bowl Gouge Wear Due To Spalt
Because spalt is comprised of mineral deposits, it is much harder than wood.
Even in the tiny lines of black zone spalt, there is enough mineral material to wear down a bowl gouge edge much faster than usual.
Expect your bowl gouge to dull faster when turning spalted wood and remember to sharpen your gouge more frequently.
Different Wood Density
Also, because the mineral deposit found in spalt is much harder than the wood fibers, the gouge will cut unevenly.
As the bowl rotates, the gouge is cutting softwood fibers, then hard mineral areas, and back and forth.
It is common to hear a clicking sound or chattering when turning spalted wood because of the different densities between the spalt and the wood.
To make smooth cutting passes, apply downward pressure to the tool rest and do not press the gouge into the bowl blank. Make fluid motions focused on the tool rest downward pressure and let the wood come to the gouge tip.
Is Spalt Dangerous?
This question does come up from time to time…
Is working with spalted wood dangerous?
Some people like to say you have to wear a special respirator and take extra precautions while working with spalted wood.
I checked with spalting expert Sara Robinson and she explained that spalted wood does not present any dangers, and working with regular wood dust is far more threatening.
Actually wood dust is more likely to do long-term damage to unprotected lungs than any spalt can ever do.
Again, most spalt is composed of mineral debris left behind by fungi. Minerals are part of everyday life for us.
Is it possible to have toxic fungi still present in a piece of wood?
Sure, I guess it is possible, just like anything is possible. But it is unlikely.
Spalting Wood Conclusion
There is probably no other natural characteristic of wood that will generate more attention and compliments than spalting.
Hopefully, this article helps you to understand this odd natural wonder a bit better and encourages you to try your hand at turning some spalted wood.
If you have a pile of wood waiting to be turned, check it for spalt. And if you don’t find any spalt, consider introducing it yourself.
Let me know what you think about spalted wood by leaving a comment below.
Check out these other articles about bowl blanks and turning:
• BOWL TURNING GRAIN ORIENTATION
• TWICE TURNING WOOD BOWLS – HOW TO STEP BY STEP
• DRYING GREEN WOOD BOWLS – 6 METHODS FOR SUCCESS
• TURNING GREEN WOOD BOWLS – THE PROCESS
• 10 PLACES FIND FREE WOOD FOR BOWL TURNERS