Why does wood change color?

Wood

WOOD

The trees are dense and the grass is lush 

The trees and the grass are abundant

After felling, the ends of logs and the bark below

Prone to discoloration

After log processing, sawn timber (board, square timber)

During storage and processing

It is also prone to blueing, browning, mildew, etc.

After wood is made into wood products

Discoloration may still occur during use

The discoloration of wood varies depending on the cause of its occurrence

Can be divided into two categories

One type is chemical discoloration, including tannin discoloration and oxidation discoloration

The other type is fungal discoloration, including mildew and blue discoloration

(Also known as green discoloration, sapwood discoloration)

Among them, fungal discoloration is more common and has more serious effects

Wood discoloration generally refers to fungal discoloration

Wood mold can cause discoloration on the surface and sapwood of the wood, but the discoloration is more superficial and is caused by colored spores. Since mold spores only reproduce and grow on the surface of the wood, the mold is limited to the surface of the wood or a very shallow layer near the surface.   

Mold often causes wood to appear green, white, black, or occasionally other colors. The discoloration caused by mold often appears fluffy or speckled. Warm, humid climates or poorly ventilated environments facilitate the proliferation of mold spores deposited on the wood surface, leading to mold growth.

The fungi that cause wood mold include Trichoderma (Tirhcoderma sp.), Penicillium (Penieillium spp.), Aspergillus (Aspergillus spp.), Mucor (Mucor), etc.   

The most prominent species of Trichoderma is Trichoderma viride, which causes the surface of infected wood to appear green. There are many species of Penicillium and Aspergillus, the most common of which is Aspergillus niger. When infected, wood develops black spots, sometimes forming continuous patches. Molds are more adaptable and tolerant to their environment and substrates than blue-staining and decay-causing fungi. They are also highly resistant to chemicals, and can even grow in contact with certain toxic chemicals. Therefore, mold can still be found on some wood after preservative treatment.

Wood mildew can cause surface discoloration, but the discoloration is shallow and can be removed with a brush or by planing away the surface. Since mildew has no significant effect on the quality of the wood itself, it is not generally considered a defect.  

However, after mold infects wood, it can increase the permeability of liquid to wood, thereby promoting the formation of blue stain.

Wood  story_

Blue-stained wood is more susceptible to decay, which will accelerate the discoloration of the wood's interior and, more seriously, reduce the commercial value of the wood.

To prevent the effects of blue discoloration, Fuqing LVL removes panels with uneven thickness, rot, blue discoloration, or severely uneven surfaces during the panel selection process. Panels containing mixed wood are also removed. After selecting the panels, they undergo a secondary subdivision to classify them into different grades, eliminating the risk of mold and blue discoloration.