Solvent Impregnated

Definition and General Information
Usually, we define this material as the part of trunks and limbs which is under the cortical layer, so it is a complex tissue with various living or non-living cells.
The most peculiar elements are:
- the vessels (tracheas) which have an extremely important function, namely the water and dietary elements conduction from the roots to the treetop
- the supporting elements, or fibres
- the parenchymatous cells, connected with various vital functions.
All those elements can still work after a certain amount of years, then they stop the vital lymph movement and some coloured substances start depositing above them; generally dark, the internal part (the oldest) seems darker and more compact and brings the name of hardwood or heartwood, while the external part, which is made of functional elements like vessels, seems lighter and less compact and brings the name of sapwood.
Wood averagely contains the 49,5% of carbon, the 6,2% of hydrogen, the 43,9% of oxygen, the 0,5% of nitrogen and the 0,5% of cinders.
Wood's colours can widely differ from a type to another: white (holly, horse chestnut, basswood), black (solid ebony), ochre (cypress, elderberry, olive tree), ferrous or brick coloured (oak, yew tree, cherry tree, mahogany), brown (walnut tree, teak), ecc.
Wood is frequently used in building construction, flooring, hydraulic elements and shipbuilding. For the buildings, the most used woods are larch, oak, pine, white or red fir.

Alteration and Preservetion
Wood reasonably resists to the effects of light and dry air. On the other hand, when there's humidity in the air, it slowly starts decomposing due to the action of fungi, which make the wood brittle and permeated by humic molecules.
Where and when the environmental conditions are favourable, some microorganisms attact the wood and disrupt its tissue, so it becomes decayed, rot and soggy.
Certain types of insects (called xylophagous) weaken and gnaw wooden surfaces and, when they're placed underwater, even some molluscs and shellfishes do the same.
Resins, tannic substances and essential oils have a preservative action: woods which are impregnated by those substances will surely maintain they're original aspect for a longer period.
When we want to extend the preservation of wooden surfaces, we usually use impregnant substances which prevent the destructive action of microorganisms.
The easier treatment is the use of oil-based varnishes, proper in order to be absorbed by the wooden tissue and containing specific substances: they lead a protective and preservative action.