Spalt is from the Germanic word for "spoiled". As woodturners, we know it as the patterns of fine black lines in Maple, the lacy patterns of red lines in Beech, various color changes, and varying patterns of different colors in different species. Spalting shouldn't be confused with the stain that sometime accompanies an invasion by insect larvae.
Spalting is a stage of rot that is stopped in time when the wood has dried. Dry wood does not "spalt", just as dry wood doesn't rot.
Some wood species spalts easilly, some spalts slowly, some species have ugly spalting patterns, some pass through the spalting stage so rapidly we can miss it before the wood is too rotten to use, and still other specied don't, or rarely, spalt at all. Cherry and Walnut are among those where spalting is rare. The same species can exhibit a different spalting, depending on where the tree grew, climate, elevation, and soil conditions.
Wood spalts for the same reason it rots, an invasion of fungal growth. Spalting and rot require four (4) ingredients - the parent fungus, moisture, heat, and nutrients for the fungal growth. Absent any one of these ingredients, there will be no spalting. Spalting occurs when all of the conditions are there for the wood to support fungal growth.
We can either let spalting develop by itself, or we can help it along by providing the ingredients for its growth. Since not all fungus is equal, nor is the resulting spalting the same, we can control the spalting pattern by either intruducing a specific fungal growth, or proividing a diet that is preferred by the growth we want.
Spalting Wood Naturally
When all of the ingredients are available in nature, the spalting process will start by itself. Throw the wood under a tree, let the grass grow up around it, and nature will take its course. Covering it with some leaves will help. Put something under it to get it off the ground, otherwise it will rot on the side touching the ground.
My method for spalting wood in Western Washington was to stand the whole length of green log on end on the grass in the shade of the north side of the house or under a tree, placing some green grass or leaves on top of it, covering it with a board or piece of plywood, and topping it off with a rock to keep the cover from blowing away, and waiting.
A Recipe for "Naturally" Spalted Wood
A "brew" of some kind is required when the conditions for natural spalting do not exist, usually from low humidity or missing fungal spores. There are a lot of ways to do this, and like everything else in woodturning, nothing is "tried and true". I encourage you experiment. Some wood spalts. Some wood just rots. Others (cherry and walnut) don't do much of anything. The following is how I do it.
This spalting brew has everything necessary for almost anything to grow in any wood that wants to spalt. I have used it on maple, birch, beech, sweetgum, oak, alder, holly, and pecan.
There is nothing sacred about any of the ingredients as long as we have the nitrogen, organics, ammonia, sugar, malt extracts, tannins, and leaf molds - everything necessary for all kinds of things to grow in the wood. The only additional ingredient is heat.
I have used packaged steer manure from the garden store and added a half cup of household ammonia. Don't use the sudsing type because it contains detergents which will kill the fungal growth.
All leaves contain some amount of tannins, oak leaves contain more than others. I have used maple, alder, sweetgum, and apple leaves, but about 3 times more than with the Oak. Wood chips will not work because you need the leaf mold. You can use chunks of rotten wood to replace the leaves, but the spalting is different with more of an area discoloration than the lines we are looking for. The large black areas look good in oak, but not other wood.
Put the wood in a trash compactor bag (they are a heavier plastic than the kitchen variety) when it is fresh cut and still wet. If the ends have dried, saw off a slice to open up the wet wood. It works better in wood cut in the spring when the sap is up and the free-water in the wood is at its highest.
Apply a liberal amount of the brew on each end, and seal the bag.
Now we will need that last ingredient, warmth. Store the sealed wood indoors under an old electric blanket during the winter months when the outdoor daytime temperature is below 65-degrees. Otherwise, outside is fine.
Check it after 2 months. You will be looking for a black slimy mess on the wood, with things growing out of it. Mushrooms are good. Clean it up and split it in half if you can. If it isn't what you want, put the halves together and back in the sealed bag.
You can use chunks or shavings of spalted wood instead of the brew, but it takes forever, and sometimes doesn't start because it is dead. The brew is faster, more reliable, and gives better spalting (my opinion).
You could just seal the wet wood in the bag without adding anything, but some will spalt, and some won't.
•1-qt water
•2-scoops Miracle grow
•2-cans beer, drink one and put the other in the spalting brew.
•1-qt horse manure, doesn't have to be fresh, but the ammonia
odor should still be present when it gets wet.
•1-qt dried oak leaves
Growing Mushrooms
We can also make spalting in the wood by growing mushrooms on it. The spalting is created by the roots of the mushroom as they seek the moisture and nutrients in the wood. We can control the patterrn and color of the spalting by the species of mushroom. We also have the benefit of growing a healthy diet, and if the spalting fails, we still have the mushrooms.
The best time to start mushroom growth is in the Spring of the year. Next spring you will have mushrooms and spalting.
Small 1/4" holes are drilled into the ends of the green wood log, and the mushrooms starts are pushed into the holes. Then the wood is placed in an environment that best suits the particular mushroom being grown. Water, shade, and warmth are needed to support the growth, and fertilizing may be required for certain species.
For more information, and to purchase the mushroom startes go to the website of Fungi Perfecti
Give them a call and tell them what you want to do. They know more about growing mushrooms and the resulting spalted wood than anything I could write here.
In North Florida I just threw the wood under a tree, let nature take its course, and hope that I could get to it before it rotted. To slow the process I always stored wood by sealing the wet wood in a plastic bag. It did spalt, and sometimes rotted, but the process was slowed enough that it took 2-years with most species.
Now that I live in a new development in North Idaho, where there are no trees, no leaf molds, humidity is too low and the fungus spores too few to support good spalting, I use a "brew" to get it started and provide the nourishment for good growth.
This the resulting spalting in a whole log section of Holly that was treated as described above in Western Washington. The tree was cut in April, and this is what it looked like when I opened it up in December.
Shitake mushrooms growing in a Birch log ihn my backyard in North Idaho. I waited too long on this log. The wood should have been cut into turning blanks and turned when the mushroom growth was just starting to develop and not allowed to mature as in this photograph.
1-qt water 
