Buying the Right
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Wood is wood isn't it? I would ask ‘have you got any wood to make a didgeridoo?’ and instead of 'yes' or 'no' I was asked loads of questions - and I didn't know the answers. I have found it invaluable to learn a little about wood before working with it. Hopefully this will be helpful for you as well.
Hardwood and Softwood
Wood is classified / divided into two categories, hardwoods and softwoods. I was wrong when I thought, as the words imply, that the difference was how hard the wood was, it isn’t. Simply put, hardwood trees surround their seed with a protective layer. Fruit trees are a good example, and so are nuts such as Sweet Chestnut. The category that defines softwoods is ‘gymnosperms’ meaning naked seed and ‘angiosperms’ , meaning covered seed. Trees are further sub-divided into families, group’s of species and singular species. Some softwoods may be more suitable for making didgeridoo’s than hardwood, however in general terms hardwood makes for better didgeridoo’s.
The Bits That Make Wood
The Pith
This is the (relatively) soft, central part, or core of the wood, surrounded by the growth rings made of heartwood and sapwood.
Heartwood and Sapwood
This is the inner part of the wood. Different species and different trees within the same species will all have different sized heartwood. When a tree grows, the part of it that is growing conducts sap. This is called the sapwood. Once the wood is established, for example the inner part of trunk of a tree, the middle of it no longer needs to grow so stops conducting sap. This is called the heartwood. In the same example, on the outer portion of the trunk, the wood is still growing and therefore you will have both sapwood and heartwood. The higher up a tree you go and/or the younger the tree the greater the amount of sapwood. Again depending on the species the contrast in colour between the two woods can be used to great aesthetic effect. About the most vivid example of this is Yew which has a very pale and light. See photo’s.
Growth Rings
Growth continues in wood so long as conditions allow. This is divided into a growing and dormant season. As this cycle of growth and dormancy repeat new layers of growth occur. These are called the growth rings.
The thickness and density of the rings depends on the species and the environment the tree grows in. Commonly accepted as a general rule, that the number of rings in the cross section of the wood denotes the age of the tree in years, this is not always the case. Some woods such as Yew can stop growing for a number of years and there have been a number of records that show certain Yew not growing for decades and even centuries. Many woods have rings that are both dark and light in colour, this is called earlywood and latewood.
Earlywood and Latewood
When you can see visible darker and lighter rings in the wood, it shows a more detailed progress of the growth. The wood that forms earlier in the year, is called ‘earlywood’ and as it is older it tends to be denser and therefore darker in colour. The lighter part of the ring is the latewood and because the cell structure is younger and less dense it tends to be lighter. As with many things in nature there exceptions to that general rule.
Cambium
There is a very thin layer between the wood itself and the bark. This is called the ‘cambium’, this is where the growth occurs. If the growth occurs inside the cambium, it adds to the sapwood, and if on the outside of the cambium then it is bark. The cambium layer changes with the seasons. During the growing time of year the cells in the layer contain more water, are more pliable and softer, with the result that bark removal is relatively easy. During winter months the cells thicken and bark removal becomes more difficult. Bare this in mind if you want to make a didgeridoo with the bark still attached, or if you wish to remove some bark for painting.
Bark
The bark as we all know is on the outside of the wood. The bark has two layers, the inner (living) and outer (dead) layer. The inner layer conducts sap and assists in the growth of the tree. The outer layer is the bark that has been replaced by new living bark. Different species produce different types of bark. It comes in all manner of textures and a wide range of colours. Bark such as that found on Yew can be deep purple in colour and be very flake, and is comparatively thin. Oak has a more constant texture, thicker and tougher. Other woods vary just as much. Double check the ends of the wood to see how thick the bark is, as I have lost a couple of potential didgeridoo’s due to the wood bring to thin after the bark has been removed.
Rays
When I first saw rays in wood I thought it was marks left by the craftsman who had been sloppy in sanding the wood. The rays are actually cells in the wood that grow horizontally. Softwoods rarely have rays that are visible, however, Hardwoods have a different cell structure and can quite be seen. In fact in some woods the rays can add to the aesthetics of the grain.
Knots
This is another of those ‘but a knot is a knot’ sections. They’re knot (ho hum, couldn’t resist). A knot originates from the pith of the wood and grows outwards from the main stem. It starts to form the branches as tree grows. The same applies to branches sporting smaller limbs. As the tree grows the branches/limbs get bigger.
When a branch or limb is detached the cambium also dies and no further grows occurs. However, as the tree continues to grow, and girth increases, the knot or broken stem, becomes encased by the new growth. Ultimately the knot can become completely encased by the new growth and not visible from the outside of the wood. What’s more, is that often bark from the outside of the broken branch/limb will also be encased in the new growth. Often the bark that is encased with the knot deteriorates in time, creating a loose knot.
This is extremely relevant to didgeridoo’s as hole’s or gaps along its length that allow air to pass through affect the sound greatly. By looking and being aware of the knots in the wood you are using, you can determine if any extra work is needed, or if they are likely to cause problems in the future.
Fungi etc
There many varieties of fungus and disease that affect timber. Not all of them are totally bad. Many only affect the colour and pattern of the wood, NOT its strength. There are the well known ones such as dutch elm disease that are harmful, and ones such as white spot which can create beautiful patterns and lines in the wood. This is often called spalting. It can occur throughout the entire piece of timber or be localised. This is dependant on the growth of the fungi spore.
When gathering some wood, I found some with what appeared to be fungal infection but I was unsure if the wood could be used so I asked someone who advised ‘try it and see’, so I collected few pieces. The pieces I collected were larger than normal so I could trim the wood down more, if the timber turned out to be poor quality. What I found was, that the sapwood was soft but the heartwood very sound. I was able to trim and shape the pieces down, removing the softer sapwood and ended up with some lovely didgeridoo’s.
One thing to note with fungi in wood is that it does not live well in certain conditions. It will not survive in wood with a moisture content below 20% (see seasoned wood page re: moisture content). It needs air to live, so when a didgeridoo is finished and sealed inside and out, helps reduce the fungi’s potential. Fungi, as a generalisation prefers to feed on sap wood. Therefore (as in the example above) allow for this when gathering the wood to assist in reducing problems later on.
It must be said that I am not a biologist and the range of fungi etc is so extensive, that I can not begin to scratch more than the surface of the subject. What I have written is what I have found out in my own quest to make didgeridoo’s and use as my own guidelines.
Few Other Useful Bits to Know
Stressed Wood
Didgeridoo's can look rather good when there is little stressed wood invloved. Often termed tension, reaction, or compression wood, it is wood that have not grown erect or ‘normally’. Though formed differently in softwood trees to that of hardwood species, the cause and effect are pretty much the same. As the tree grows, it can become stressed for a number of reasons, it could be encumbered e.g. weight of snow or ice on the limbs (colder climates), to partial uprooting in storms (either the tree itself or a tree leaning against it), to sunlight being available from only one direction. Whatever the reason for the ‘stress’, the results are similar. The wood is affected in that it grows with abnormal or irregular growth rings, with the pith not being central.
When the wood subsequently seasons and dries out it will shrink, twist and warp unevenly. Consider the didgeridoo. When cutting in half to hollow out, if the wood is stressed, and you cut along the stress line, the wood can ‘ping’ apart instantly and it nigh on impossible to glue the pieces together snugly. Don’t forget that the distortion can happen in three dimensions, not just twist or move one way. When cutting stressed wood you may find that the surface is burred (similar to that of cutting wet wood with a blunt saw).
Stressed wood can also add significant character to the didgeridoo if thought of before hand. When shaped, the growth rings will appear irregularly so it can be shown of to great effect.
Grain
Couldn’t write this without mentioning grain. Knowing what you are looking at and how something is formed will help immensely when working the wood. The grain of the wood depends on the species of tree and the growing conditions of the tree. I have read that there are over 50 different uses of the word grain and many sub-categories. The description of the grain depends on the surface of the wood, or how it has been cut, e.g. across the width of the wood, along the length of the wood, and so on. Needless to say (but I have anyway), you do not need to know them all so I will only cover the most important ones:
Cross (or End) grain is when the wood is cut perpendicular to the axis of growth, ie it grows up, you cut it across. This cut shows you the growth rings of the tree. It is known as the transverse or cross-sectional surface. In didgeridoo terms this is when you trim the length of the wood down.
Radial surface is when the wood is cut vertically through its middle. This surface or cut shows the growth rings as vertical lines and knots will appear horizontally. This is produced when cutting a didgeridoo in half, prior to hollowing.
Tangential surface is when the wood is cut vertically but the cut does not pass through the centre of the wood. Basically it is cutting a vertical slice off the wood. In didgeridoo terms when shaping the wood down, you would trim the bulk by cutting slices from it, along the tangential surface.
Knowing the grain will surrender much information such as the age of the wood, the type or species of the wood, whether it is stressed or not. It will show you the original shape of the timber and tell where branches and limbs grew, and so on. I remember speaking to one didge maker who started telling me about the wood and describing what and where it had had limbs growing, the original shape of the wood and so on. I thought ‘how?’, then thought ‘why’, then went away and found out! (thanks Ant).
