what is water logged wood prosses in conservation
Answers
When water evaporates from wood that has been saturated for centuries and is partly decomposed, the wood shrinks and distorts. This picture shows an untreated fragment of Iron Age wood, excavated in about 1914, allowed to dry naturally.
Wood is stabilized by replacing the water with impregnants that also add strength to the decayed wood. The aim is to preserve both the shape and the surface detail. It has, however, proved difficult to find preservative materials that do not themselves destroy the wood in the long run.
This article describes the search for the perfect preservative, based on the conservation processes used in the National Museum over the past hundred and fifty years.
Drying oil
One of the earliest methods used in Denmark for conserving wood was to impregnate the wood with a mixture of petroleum and a drying oil, preferably linseed oil, while the wood was allowed to dry slowly. Linseed oil does not penetrate well and it breaks down in time, so that the surface of the wood becomes sticky and dark.
Glycerin
Impregnation with glycerin was another early method, used from 1900. It was used either pure or in combination with other materials. Glycerin is a water like molecule which easily replaces the water in the wood but evaporates extremely slowly. Air does not enter the wood, so the shrinkage which is caused by the surface tension at the interface between air and water does not occur.
Glycerin absorbs and releases moisture as the atmospheric humidity changes. It gives the object a wet and sticky appearance. It does not strengthen the wood and therefore gives inadequate protection against collapse.
Alum conservation (1859-1958)
A new method of wood conservation with alum was published by C.F.Herbst in the Antiqvarisk Tidsskrift of 1861. It became the National Museum's standard treatment for waterlogged wood for the next hundred years.The principle of the process is that alum (potassium aluminium sulphate with water of crystallisation) is a solid crystalline substance at room temperature but when heated it dissolves in its own crystal water. The potassium, aluminium and sulphate ions will diffuse into wood that is immersed in the warm solution, eventually acquiring the same ratio of ions to water as in the crystalline solid. When the wood is cooled again, alum recrystallises, incorporating all the water in its own crystals, whose bulk prevents the wood from shrinking. The process was completed by brushing the object with warm linseed oil and finally with a thin coat of shellac. This was to prevent absorption of water from damp surroundings.
Answer:
This is because wooden logged removed the water which is equal to the weight of wooden logged.
This happens due to the law of "Archimedies".