Oxidizing Tannins in Woods

A common problem found working with reclaimed or old cut lumber is the need to clean up and mill the wood while maintaining the weathered appearance. Whether one is making a new project, or trying to match the wood in an older piece, the grayed out “old look” can be a challenge to achieve.

One way to achieve some degree of success is to artificially oxidize the wood. This process is similar to the one that happens naturally with age and weather exposure, but is much easier to control, and gives almost instant results. The oxidation process is a chemical change in the wood; it’s not a stain, and won’t interfere with finishing at all.

To start, you’ll need to dissolve 0000 steel wool in a jar of white vinegar. A number of brands of steel wool come lightly oiled to prevent the wool from rusting, and will need to be washed in soapy water before soaking in the vinegar. Close your jar, and wait a few days. The longer you wait, the more wool will dissolve, until it is all integrated into the solution.

The next step is to strain the mixture through a paint filter to remove any remaining solids. The actual oxidation will not react with finish, but any undissolved bits of steel wool may. Additionally, when working with open pored woods like ash or oak, any solid wool pieces can get stuck in the grain. It’s important to have your “rusty vinegar” as pure as possible.

Some woods, such as oak and walnut, have naturally occurring high tannin content, which means you can apply the oxidizing solution at this point. Some woods, however, do not have enough tannins to make much of an impact with oxidation. For these woods, such as pine and maple, an intermediate step is required to impart tannins into the wood. If you brew up a double-strength cup of plain black tea, you’ll end up with enough tannins to react with the solution. Let the tea steep for an hour or so (until the boiling water cools off), take the bags out, and wipe on to the wood. This step may raise the grain, so let it dry, sand down the whiskers, and apply another coat of tea.

After your wood has enough tannins, it’s time to apply the solution. You don’t need to soak the project; a light wipe-on coat will work just fine. With some woods, the change is almost instant. With others, you may have to wait a few minutes as it darkens. If you test a piece and it comes out too dark, you may want to dilute your solution a bit with more vinegar. Once the wood reaches the level of oxidation you like, you can wipe off the remaining solution with a damp rag.

By Kyle VanDewart - Denver Store Sales
Photo courtesy of thedesigntabloid.com

oxidized tannins in wood
April 09, 2019 — Alana Mace