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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.
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