We’ve already explored the impact of weeping sap, rot-resistant extractives, and tannins on wood (see Part 1 & 2). In this final article of our series, we’ll take a look at the way oxidizing chromophores affect the appearance of wood.
Oxidizing Chromophores can dramatically change the color of lumber boards. Chromophores are molecules located in the wood that make it appear a certain color. As these chromophores, which are made up of various extractives, get exposed to oxygen, the color of the wood can change completely.
Teak is a classic example of this phenomenon. It can end up turning gray, green, or purple after going into the planer a rich brown color! This happens when the chromophores in the oil and silica-rich Teak are exposed to oxygen. Thankfully, the results of this oxidization are often short-lived. Once the chromophores bond with the oxygen in the air, the golden brown color should return in short order. If you’re not expecting to see it, though, the oxidization of Teak can come as quite a shock!
Cherry wood’s oxidization causes it to turn from pale pink to a rich brown with pink overtones. Purpleheart is another common example of chromophore oxidization causing a major change in the appearance of wood for a short time after planing or sanding. The bright purple color that gives this wood its name eventually deepens to a rich reddish-brown hue.
As long as you understand that wood’s chromophore oxidization causing a change in color is only a temporary result, it shouldn’t be too much of a problem. Sunning a board can speed up the process. Finishing a board that’s just been milled can slow the process down and therefore isn’t usually recommended.
Extractives are present in every species of wood to varying degrees. Some extractives, such as the delicious syrup extracted from Maple wood or the tannin found in Walnut, don’t significantly impact the lumber that’s produced from these species. Of course, that’s a general assessment. There are always exceptions, and sometimes species not typically known for being negatively impacted by extractives will surprise you with an occasional extractive-rich board. That’s the adventure of working with wood. As an organic product, it can be rather unpredictable!
Extractives are sometimes extremely beneficial to wood. Teak is chosen for marine projects because it has silica and oil-rich extractives that render it nearly waterproof. Oil and water resistance due to high extractive levels make tropical hardwoods an ideal choice for outdoor applications where they’ll need to endure exposure to the elements. As long as they’re treated appropriately to combat the negative effects of their extractives, these wood species can be successfully used in a variety of applications.
When it comes to wood extractives, there’s both positive and negative aspects of these natural substances. The key is to identify which ones are likely to be found in greater or lesser amounts in different wood species and plan accordingly. As long as you take proper measures to mitigate staining and color transference and allow time for chromophore oxidization before applying finish to your boards, the wood should perform just fine. That’s why informing yourself about whatever species of wood you plan to use, not to mention choosing the correct species for your application, is an essential element to the long-term success of your project.
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J. Gibson McIlvain Company
The McIlvain family has been immersed in the premium import & domestic lumber industry since 1798. Headquartered just outside of Baltimore, the J. Gibson McIlvain Company is one of the largest U.S. importers of exotic woods. As an active supporter of sustainable lumber practices, the J. Gibson McIlvain Company has provided fine lumber for high profile construction projects worldwide. Call (800) 638-9100 to speak with a J. Gibson McIlvain representative.