What Does Vinegar Do To Untreated Wood?

Woodworking is an ancient craft, and vinegar has been intentionally made for perhaps 7,000 years. But people, who developed both, are pretty much the same through the ages. Today's online influencers seem to share the same questions as the ancients: Where do we come from? Why am I here? Why am I so soft in the middle when the rest of my life is so hard? And what happens when I put vinegar on something? 

So the question of what vinegar does to untreated wood was bound to come up. The answer is, it does a few things. Bleaching or darkening, modifying the surface texture, and making it flexible. As an expert woodworker I've used vinegar in my craft for decades. Coloring wood with high tannin content most often, but there are other uses that can be very handy.

How can vinegar do all those things to raw wood? It's chemistry. Vinegar contains acetic acid. Commercially distilled white vinegar is usually about 5% acetic acid, though both white vinegar and applie cider vinegar can vary in their percentage. This mild acid is the key to its popular cleaning and antiseptic properties. It is also what interacts with the fibrous substance that makes up wood. 

Think of wood as thousands of straws packed tightly together. Those long rigid straws are made up of a naturally occurring polymer called lignin. The acid in vinegar temporarily softens the lignin cells, changing the surface of the wood and letting the acid interact with other chemicals such as tannins within the wood fibers. Woodworkers can take advantage of that softened state in a few ways.

I mentioned earlier that I use vinegar in a wood staining hack. Soak nails or steel wool in vinegar overnight to create a solution containing iron acetate, then apply it to tannin-rich woods like oak or cherry and the wood will darken in just seconds. The vinegar softens the surface allowing the iron acetate to reach cells containing tannin, which then react by darkening. The intensity of the solution and the tannin content of the wood fibers will determine the degree of color change. 

Less dramatic than the tannin process is letting the vinegar bleach your wood, lightening the color. The results are subtle. You can also "age" wood with vinegar. As wood is exposed to the elements, some of the lignin is eroded away. If you soften the surface of a wooden board with vinegar and then, using a stiff bristle brush, scrub it with the grain, you can remove some fibers, mimicking the natural aging process. Many folks like this aged and distressed look for certain projects.

The most fascinating woodworking trick you can do with vinegar is to bend wood. As I said, soaking wood in vinegar will temporarily soften the lignin (the ridged superstructure of wood). Most of the time we want wood to stay strong and ridged, but if you soften the lignin, with steam or vinegar, you can then bend a piece it in a form (photo above) and allow it to harden into that shape. Think of Windsor chair rails, toboggans or old-fashioned skis. Bending wood for something like a chair rail saves material and adds a useful element to a woodworker's bag of tricks.