Big word, but it perfectly expresses the relationship between trees and fungi. They live off each other. Not all fungi of course. Particular trees have particular fungi. Often they feed on the living tree, but when the tree dies they begin to take over. It takes time, but they feed on the sugars in the sap, and eventually begin to break down the cell structure - the wood rots.
But even in the living tree the external efflorescence can mask the fact that the fungal growth has penetrated deep into the wood. And as it changes the chemistry, it changes the colour. The result can be subtle variations, or spectacular patterns called spalting.
One wood particularly prized by turners when it is spalted, is beech. That is because one of the fungi to which beech is susceptible produces black zone lines which contrast dramatically with the creamy brown of the wood.
A couple of years ago i was fortunate enough to acquire a large four inch plank of spalted beech from a woodyard in Suffolk. Last year I turned a big shallow bowl from part of it, but I had been hoarding the largest piece until I was ready. Mid February this year seemed like a really good time, so I loaded a circular blank into the lathe.
I wanted to get the maximum diameter on the upper surface, but the natural convolution of the tree meant that I could only have this at the price of a thin wide rim. That was OK because I wanted to display the spalting at its best - which the rim would allow me to do.
So the first challenge was to get rid of the bark from the under side.
Here you can see the spalting patterns beginning to emerge up and down the grain of the wood.
By now I have largely eradicated the bark whilst retaining a reasonable stock for the central cup of the bowl.
With the bark all gone you can see the beauty of the spalting patterns, at least on the underside.
It's now time to turn it around and cut the upper surface. Usually what I would do at this stage is turn a small plinth or spigot at the base so I could then grip the base in a contracting chuck whilst I turned the inner side.
But the blank was only four inches when I started, and I didn't want to lose any of the height of the finished bowl. So instead I cut a recess to insert an expanding chuck to grip it.
The danger of doing it this way is that as you expand the chuck the pressure is trying to split the wood apart. And this was a big, heavy piece so I had to be sure that it was held securely and not likely to fly out of the lathe. The recess for the chuck had to be quite big and quite deep, creating the other danger that when the inside was being hollowed I might cut right through, and I wanted to make a bowl, not a wheel!
Fortunately I got the pressure just right and could start to turn the top, albeit at slow revolutions. One dig-in and the bowl might have split, or just flown out of the lathe and smashed.
So far, so good. But wood is not a homogeneous substance. As its growth speeds up and slows down throughout the year each ring has a soft part and a hard part. And when a fungus invades a dead or dying tree it softens the cell structure differentially. So with spalted wood in particular you get softer areas and harder areas.
Look at the bottom left of the above picture and you will see what appears as a dent in the rim. This is a particularly soft part of the wood, and the final sanding has scoured away too much of the thin rim. So. it's time to cut it off, and shrink the final size of the bowl.
This is the result.
And different lighting conditions draw out the drama of the spalting.
You can see that I deliberately raised a rim on the edge of the inner bowl, and undercut it with a surface which starts nearly vertical. That not only increases the play of light on the bowl, but reveals quite different patterns as the angle of the curve changes.
Working this bowl took a lot of time and care, but I think it was worth it.