Why does wood change color?

Wood

WOOD

Trees grow in abundance and grasses flourish 

The trees and the grass are abundant

After trees are felled, the ends of logs and under damaged bark...

It is prone to discoloration

After processing logs, sawn timber (planks, square timber) is produced.

During storage and processing

It is also prone to blue staining, browning, and mold growth.

After wood is made into wood products

Discoloration may still occur during use.

The discoloration of wood varies depending on the cause.

It can be divided into two categories

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

Another type is fungal discoloration, including mold and blue stain.

(Also known as sapwood discoloration)

Fungal discoloration is more common and has a more serious impact.

The discoloration of wood generally refers to fungal discoloration.

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

Mold often turns wood green, white, or black, and occasionally other colors. Discoloration caused by mold often appears as flocculent or spotted patterns. In warm and humid climates, or in poorly ventilated environments, mold spores deposited on the wood surface easily multiply and grow into mold.

Fungi that cause mold growth on wood include Trichoderma (Trichoderma spp.), Penicillium (Penieillium spp.), Aspergillus (Aspergillus spp.), and Mucor.   

The most prevalent fungus in the *Trichoderma* genus is *Trichoderma viride*, which turns the surface of wood infected with this fungus green. The *Penicillium* and *Aspergillus* genera contain many species, the most common being *Aspergillus niger*, which causes black spots to appear on the surface of wood infected with this mold, sometimes merging into patches. Molds are more adaptable and tolerant to their environment and substrate than *Gynostemma pentaphyllum* and *Pseudomonas aeruginosa*, and they also exhibit strong resistance to chemical agents, even continuing to grow when in contact with some toxic chemicals. Therefore, mold can still be found on some preservative-treated wood.

Mold can cause discoloration on the surface of wood, but the discoloration is usually minor and can be removed with a brush or by planing off the surface layer. Since mold does not significantly affect the quality of the wood itself, it is generally not considered a defect.  

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

Wood  story

Blue staining makes wood more prone to decay, accelerates internal discoloration, and, more seriously, reduces its commercial value.

To avoid the effects of blue stain on the wood, Fuqing LVL, during the panel selection process, not only rejects panels with uneven thickness, but also those that are rotten, have blue stain, or have severely uneven surfaces. Panels containing mixed wood are also rejected. Based on the selected panels, a second sub-classification process is conducted to grade the panels, eliminating the risk of veneer mold and blue stain.