Wood of many tree species will change color when exposed to high moisture content or for a prolonged period of exposure to moist air, not caused by fungal infestation of wood, but caused by chemical reactions in certain components of the wood. It is called chemical discoloration. Oxidative condensation of tannins, pigments, alkaloids, sugars, phenols, and other organic substances in wood, the most important of which is the oxidation of phenolic compounds in wood.
Phenolic compounds have a benzene ring structure and are easily oxidized, which is the cause of chemical discoloration. Phenolic compounds are colorless prior to oxidation, and some are soluble in water. After oxidation, they form water-insoluble condensates in red, reddish brown, and brown colors. Therefore, chemical discoloration is also called oxidative discoloration.Some phytochemicals contain tannins, also known as plant tannins, which are mixtures of polyphenols. When exposed to iron under humid conditions, the tannins and iron undergo a chemical reaction (complexation reaction) to form tannic acid. iron. Black tannin iron is the main raw material used to make the ink, thus making the wood darker in color. According to the amount of iron and the length of time that the wood is in contact with the iron, the color of the wood changes from light grey to blue-black.
Similarly, when the wood is soaked in water with high iron content, the wood also undergoes such chemical discoloration. In addition, the wood is in contact with copper or copper tabloid. Since the tannins in the wood react chemically with the copper and generate copper tannin, the wood also changes color (light red). Chemical discoloration often occurs during drying of wood. This is mainly due to the slow drying of the wood, especially at the parts that come into contact with the wood. Chemical discoloration is characterized by shallow depth of discoloration and more uniform discoloration.