Why does wood change color?(1)
The discoloration of wood, simply put, is the color change on its surface due to the action of the environment (sunlight, oxygen, moisture, temperature) and microorganisms (fungi). Discoloration can occur on logs, sawn timber, and wood products.
After the trees are felled, the ends of the logs and under the bark that are not intact are prone to discoloration. After the log is processed, the sawn timber (board, square timber) is also prone to bluing, browning, mildew, etc. during storage and processing. After wood is made into wood products, discoloration may still occur during use.
There are many types of wood color changes, from the natural color of the wood (white/yellow/light brown, etc.) to pink, red, blue, green, gray, dark gray, brown, taupe, dark brown, black, etc.
The discoloration of wood can be divided into two categories due to different reasons, one is chemical discoloration, including tannin discoloration and oxidative discoloration; the other is fungal discoloration, including mildew and blue stain material discoloration). Among them, fungal discoloration is more common, and the impact is more serious. Generally speaking, wood discoloration refers to fungal discoloration.
1.Chemical discoloration of wood
The discoloration of many species of wood when their moisture content is high or when exposed to moist air for a longer period of time is not caused by fungal infection of the wood, but by a chemical reaction of certain components in the wood. , called chemical discoloration.
Oxidative condensation reactions of tannins, pigments, alkaloids, sugars, phenols and other organic substances in wood, the most important of which is the oxidation of phenolic substances in wood.
Phenolic compounds have a benzene ring structure and are easily oxidized, which is the cause of chemical discoloration. Phenolic compounds are colorless before oxidation, and some are soluble in water; after oxidation, water-insoluble condensates are formed, and the color is red, reddish-brown, and brown, so chemical discoloration is also called oxidative discoloration.
Some woods contain tannins, also known as vegetative substances, which are mixtures of polyphenols. When contacted with iron under humid conditions, the tannins and iron will undergo a chemical reaction (complexation reaction) to form iron tannins. . Iron tannin is black in color and is the main raw material used to make ink, thus darkening the color of the wood. Depending on the amount of iron and the length of time the wood has been in contact with the iron, the color of the wood changes from light gray to bluish black. Likewise, this chemical discoloration of wood can also occur by soaking wood in water that is high in iron.
In addition, when wood comes into contact with copper or copper alloys, the tannins in the wood react chemically with copper to form copper tannins, which will also discolor the wood (light red).
....................... To be continued...................................
Our company produce conventional drying kiln, heat pump wood drying kiln, veneer drying kiln and so on drying equipment. If you are interested, welcome to contact us.
