Wood – the ecologic material
The basic elements of timber are : coal (49.5% ), oxygen (43.8 % ), hydrogen (6.0%) , nitrogen ( 0.2% ) and others. The main compounds of wood are cellulose (about 45%) , hemicellulose ( 30% ) and lignin (about 20%). In addition, there are also sugar, protein , starch , tannins , essential oils , rubber and minerals in wood which, when burnt, become ash . The chemical composition of ash depends on the type of tree , climate , soil , etc
Durability of wood
A sample hardness measured by the Janka’s hardness test(using a 1 sq. cm cross-section metal ball) at 15 % moisture content , for certain species of wood is , from softest to hardest :
- Pine – 28-30 MPa ,
- Alder – 43 MPa ,
- Birch – 48 MPa ,
- Oak – 66-77 MPa a(higher value for the so-called heartwood )
- Nut – 72 MPa ,
- Ash – 72-75 MPa ,
- Beech – 78 MPa ,
Hard wood is often most resistant to abrasion. This feature is important when choosing the wood as a material.
The color of wood
In the wood of our tree species there are six main types of color :
- The color close to white – fir , spruce , aspen , hornbeam , beech , maple , sycamore
- The yellow color – birch, stone pine
- The color brown – oak, ash , elm
- Different shades of red – yew, larch , pine , cherry, plum
- A greenish color – locust
- The color close to black – walnut, ebony
The color of the wood , except its species may also be affected by climatic conditions and, to a lesser extent, soil.
The sapwood is uniform throughout the cross-section of bright color with darker colored layer outlining the late wood and a lighter layer of the early wood . In the wood of heartwood species there is a clear difference between the brightly colored sapwood and darker heartwood.
In the northern part of the temperate climate there is dominance of the species with the brightly colored wood (spruce , birch , aspen) . In the southern part of the zone there are species of trees whose wood has a larger variety of colors and shades (oak , ash, plum , larch ). Finally, the largest range of colors and shades of the wood can be found in the subtropics ( green and black ebony tree magenta ).
The color of wood changes because of light and the weather. The alder takes a red brick colour in a few hours after being cut off .The reddish yew wood takes on a purple hue with time . The prolonged exposure to water makes the tannin-containing wood take on the characteristic color ( the oak blackens). Finally, various atmospheric conditions make the majority of wood species go grey.