Dealing with Discoloration on Wood Packaging Products: Know the Difference
When you come across black discoloration on your wooden packaging products, it can be a cause for concern. At first glance, it might appear to be mold fungi, but the truth might surprise you. Understanding the distinction between various discolorations could save you valuable time, money, and undue worry.
For instance, there are fungi types known as bluestain that can grow on lumber, and they do not pose any human health risks. Interestingly, some naturally occurring defects in lumber may resemble mold but are not biological in nature.
Before hastily approaching your supplier to replace all your wooden pallets, it's crucial to be aware that many naturally occurring, non-biological defects can give a frightening appearance but are not caused by microorganisms such as fungi or bacteria. Let's delve into the different types of discolorations you might encounter:
Identifying Wood Discolorations
1. Iron Stain (Tannic Acid)
Iron stain is a common discoloration found on wood, especially in oak, redwood, cypress, and cedar, which contain substantial amounts of tannin-like extractives. This discoloration occurs due to a reaction between these extractives and iron-containing materials, such as metal fasteners and sawblades. The staining spreads through water movement, and it's less pronounced in woods with low moisture content. Importantly, iron stain is purely cosmetic and doesn't affect the wood's structural integrity.
2. Brown Stain or Zebra Stain
Brown stain or zebra stain is specific to western hemlock and typically emerges after the wood undergoes kiln drying. Unaffected areas appear light yellow, while affected areas turn dark brown, leading to noticeable surface color differences. In some cases, the brown stain may even turn black after drying, which is referred to as zebra stain. This transformation occurs when iron or manganese compounds darken the brown stains.
3. Sun Exposure (Weathered)
Sun exposure can chemically alter the tannins in wood over time in response to UV rays from the sun. This weathering process is common when wooden products are left outdoors and exposed to sunlight. As a result, the wood darkens, similar to a sun tan, potentially making it appear dirty or damaged.
4. Bluestain
Bluestain, unlike mold, is a common cause of lumber discoloration. It results from the presence of certain dark-colored microscopic fungi in the sapwood of trees. Contrary to its name, not all bluestains are blue; they can manifest in various shades, including blue, bluish-black, gray, brown, red, yellow, orange, or purple. Importantly, bluestain has no detrimental impact on lumber's performance or strength and poses no health risks. It can be used for the same purposes as non-stained lumber and is safe to handle.
5. Enzymatic Discolorations
Enzymatic discolorations are commonly observed in hardwood species like red alder, oaks, beech, and maples. These discolorations result from the reaction of enzymes or polyphenolic compounds within living cells, producing a grayish or brownish tone in the sapwood1.
6. Mineral Discolorations
Mineral discolorations typically appear as dark lines or streaks in oak, green or brown patches in sugar maple, or purple to black areas in yellow poplar. They sometimes develop in standing or fallen trees located in mineral-rich soils.
Preventing discolorations caused by iron stains and weathering is manageable. If you store wood products outdoors, it's advisable to keep them covered yet ventilated to prevent weathering1.
In conclusion, understanding the various types of discolorations that can affect your wooden packaging products is essential for making informed decisions about maintenance and replacement. By differentiating between these discolorations, you can save valuable resources and alleviate unnecessary concerns in your business operations.
Sources
- "Is it really Mold?" - National Wooden Pallet & Container Association.
- "Iron Stain flyer" USDA Forest Products Lab.
- "Blue Stain Tech Sheet" USDA Forest Products Lab.