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.