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or many companies, discovering black discoloration on your wood packaging products can be troublesome. At first glance it might look like mold fungi, which are a great cause of concern regarding human health, but it might be something else entirely. There are types of fungi that grow on lumber called bluestain but they are not linked to human health concerns. Interestingly, there are also other types of naturally occurring defects in lumber that might look like mold but in fact are not biological. Before you "jump the gun" and ask your supplier to replace all your wood pallets with fresh ones, keep in mind there are many types of naturally occurring, non-biological defects that may look scary, but are not caused by microorganisms (fungi, bacteria, etc). Understanding the difference could save you time, money, and a great deal of worry. The report "Wood Discolourations & Their Preventions, with an Emphasis on Bluestain" discusses the different types of discoloration commonly found on wood products and how to identify them. Iron Stain Iron stain is considered the most common type of black stain found on wood products. According to the report, "it is caused by elemental iron reacting with phenolic chemicals in the wood to form black iron tannates, or common black ink pigment." In other words, if particles of iron are deposited on wood during railway transport or if steel wire, staples, or nails are in direct contact with wood and the wood becomes wet, the wood might become stained dark with iron. Even saw blades will sometimes cause these streaks. Brown Stain or Zebra Stain In western hemlock, a type of discoloration occurs only after the wood is dried in a kiln. Whereas the unaffected areas appear light yellow, affected areas appear dark brown, making for noticeable differences in surface color variation. Below the surface of susceptible pieces, sometimes the brown stain will appear black after the wood is dried. This is known as zebra stain. Zebra stains happen when iron or manganese darkens the browning and makes it turn black. Bluestain Bluestain is the most common type of fungi found in wood products that is commonly confused with mold. Unlike mold fungi, bluestain is not linked to human health issues. Bluestain is not F Is it Really Mold? BLOG Photograph by Wikimedia; distributed under a CC-BY 2.0 license 38 PalletCentral • March-April 2018 palletcentral.com Blog by Annie Montey