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             Technique

Blanks
I only turn woods grown in our native country, trees that are cleaned from forest, orchards or gardens. 
Mostly I am using fresh wood as blanks for my turnings. But up to day I have had plenty of wood, so there have always been logs lying outside to be coloured by fungi.

The fungi living from plain carbohydrate in the cells start making the different stains, later other fungi that attack the wood and split cellulose and lignin. If this process goes too far the strength of the wood will be too low to use it as a blank for turning. 

The fungi have their optimal condition by a temperature between 10o C and 32o C and moisture content between 30 % and 100 %. Therefore keep the bark on if you are trying to stain the wood by fungi. The problem is that you cannot inspect how far the colouring process has gone unless you cut off a piece. There are many factors affecting the result, the kind of wood, what time of the year the tree is cut down, temperature and moisture content and what kind species of fungi who are doing the job. So the turners sometimes fail in making an interesting blank.

Green turning
I green-turn the blanks before they are dried. In this way I can remove most of the wet wood so the drying process does not take too long time. During the green turning I make a decision about the design of the bowl, bowls with turned edge on the top, bowls where the natural edge under bark is the rim or bowls where the bark edge is showing. Sometimes I finish the bowls wet with a thin wall and let them dry and warp showing a good or perhaps a poor result.

Very often you will notice cracks starting near the pith. On the band saw or by the chainsaw I divides the piece of the
log along the heart and make it a little rounder before I put the blank between the four prong drive centre and the tailstock and shape the outside of the bowl and make a holding for the chuck with a outside or inside grip. If my intension is to make a natural edge or bowl with bark edge I "turn" the blank and put the drive centre at the bark side. Very often I have to adjust both the placing of the four-prong drive and the tailstock to have a better balance of the wooden piece or achieve the design I am looking for. 

If you want to make a bowl with bark edge you have to take care of the physiological condition of the tree. If the cambium layer between the bark and the sapwood is active, the bark will not "hang on" so cutting down the tree the right time of the year is important.

Drying.
When you greenturn you have to dry the rough turned items afterwards. You can do this by different methods. You can use a regulated kiln if you have access to one, or let the rough bowls lie in a cool room and later move them over to a heated room or you can use a microwave oven to dry small pieces. I place my green turned objects in a relative cool room, By following the weight of the pieces I can find out when they have stabilized against the given temperature and relative humidity in the room. ( The equilibrium moisture content. EMC) To take the wood down to acceptable moisture content I then move bowls over to a room where I have a dehumiditifier and a higher temperature.


Shrinkage. When you dry green turned wood it will shrink. The time you cut down a tree it may have water content more than 100 % of completely dry material. When all the free water have gone the tree has reach the fibre saturation point containing 28 % - 32 % water content. Further drying will start the shrinkage. There are differences between the shrinkage along the growing direction, the tangential and radical direction. This will end up with stresses in the wood which may give cracks or the distortion may be so great that the blank is unfit for use. 

The tangential shrinkage is the greatest and may for different woods vary from 5 % to 12 %, the radial shrink is about the half, and the shrinkage along the growing direction is less than 0.5 %. If you have sufficient data it is possible to calculate how many millimetre a bowl with a given diameter will shrink during the drying period.
If you increase the wall thickness by a factor of 2 the drying time increase by a factor of approximately 4. Here you must take into account the fact that moisture moves about ten times as fast lengthwise (in the growing direction) as crosswise. To get an event drying of green turned bowls you have to close the end grain so the diffusion in this direction is slowed down.

The final turning
When the green turned bowl is dry it is time to put it in the lathe again. To get a good finish the item must be really dry. Especially in cases where you are working with softer hardwood like aspen
, the moisture content by preference should be below 10 %.
A dry green turned bowl will have a more or less oval form so the first I do is to make it round and I usually sand the outside before I complete the inside. Sanding takes a lot of time. One should sand as little as possible and do the work with sharp honed tools. I usually end up with grit of 240 or 320 and if I have hard woods, which I will polish, I end up with an even finer sanding paper. I prefer to end up with my products showing a satin surface with no sign after a coarser sanding paper.

Colouring.
My choice is to have my products in their natural colour. But I also use the nature to colour my blanks, storing the wood outside will give the natural bacteria and fungi the opt unity to attack the wood. This way of "staining" the woods will end up with a spalted item having the most fantastic pattern. But I have also been working with water-, spirit-, or oil based stain and staining by chemical treatment. Some wood like oak contains tannin. If you brush on a solution of iron acetate the surface will get a nearly black colour. (You can make iron acetate by dissolving steel wool in vinegar, filter the solution before use.) You can treat other kinds of wood by applying a solution of tannin (catecol or pyrogallol), let it dry and brush over a solution of metallic salts, different metals will make different colours.

But what engage me most is to add colour to the growing tree, giving me a tree coloured in the sapwood from the ground to the top. In this way I can create different hue of colour and because of the colour following the veins it makes many patterns due to faults and knots in the wood. The colour will find the way to cellulose in the wooden cells and by covalent and electrostatic chemical connection stay stable, it will not fade. I started my "research" in 2000 and I am not yet satisfied. In the future there will be more work and tests. I am the only one in Norway colouring wood in this way and making this kind of unique coloured wooden bowls.

On most of my products I am using oil based on natural resins, which are dissolved. This solution will soak in the wood and harden. On some item I am using lacquers, but mostly on objects where I have used stain, artist colours or paint.