I love natural wood tones and most of the time I just use oil or wax-based finishes which do not stain the wood. Yet sometimes a project calls for a contrasting color. In this experiment, I want to try a technique called ebonizing to give wood a black finish.
Why Ebonize Wood and Not Just Use Black Paint?
The simplest way would be to just use black paint to cover the wood but I remembered a woodworking article I read some time ago about ebonizing wood. What really stood out to me was how ebonizing preserved the texture of the wood. You get a black surface but the wood grain is still visible.
How does Ebonizing work?
Ebonizing wood is a pretty old technique. It has been used to create substitutes for real ebony wood because ebony is pretty rare and thus expensive. The classic method for ebonizing is based on a chemical reaction between iron acetate and the natural wood tannins which produces a dark stain.
Iron acetate can be easily made at home by placing some steel wool in a jar filled with regular vinegar and leaving it there for a few days. When the vinegar solution is brushed onto the wood it reacts with the tannins. The darkness of the resulting color depends on the tannin content of the wood. Some woods like oak or walnut contain a lot of tannins and will turn fairly dark, while woods with lower natural tannin content like birch or maple will get a more gray or brownish color.
Material to Ebonize Wood
I had some panels of birch plywood at home and wanted to see how dark of a finish I would be able to get with ebonizing. As birch is a wood type with low tannin content, it is necessary to add tannins if you want a color close to black.
The article mentioned above described soaking the wood with bark powder tea which contains a lot of tannic acids, as a method to increase the amount of tannins present in the wood.
I will be trying two different methods for this. The first is just a strong brew of black tea. For the second one, I collected walnuts husks from a tree nearby and put them in a jar with some water. Here is a complete list of all the material I used:
- 3 mm Birch Plywood (cut into small pieces)
- Household Vinegar
- Steel Wool
- Black Tea
- Walnut Husks
- Old Paint Brushes
- Glass Jars
- Sandpaper (120/180/240 grit)
Preparation of the Material
Okay, enough theoretical explanations, let’s start making something!
The process is fairly simple. It just takes some preparation. I started by washing the steel wool. There are oils in on the steel wool from the factory so that it doesn’t rust but these oils also slow down the reaction with the vinegar. The steel wool is then put in a jar with vinegar and let it sit for about a week. Gas builds up inside the jar so don’t tighten the cap. I also mixed the walnut husks with some water at the same time.
After a week I filtered both solutions through a coffee filter (I used a separate filter for each). The vinegar/iron solution had a rusty orange color and the walnut solution was a deep brown. Next, I made a strong bew of black tea by using only about one-fifth of the normal amount of water for a cup of tea.
My wooden test swatches were sanded to 180 grit. Then wetted with water to raise the grain and sanded again. This way, the grain should not raise when I apply the solutions.
Applying the Different Solutions to the Wood
I made seven different test swatches:
- Untreated Birch Plywood: The swatch in the top row is the original untreated birch.
- Black Tea: I applied two coats of black tea. The color change is very subtle. It made the wood slightly darker and gave it a bit of an orange/yellow tint.
- Walnut: To the third swatch applied two coats of the walnut husks solution. The result is a medium brown color.
- Iron Solution: The vinegar/iron solution directly applied to the untreated wood.
- Black Tea and Iron Solution: I first applied two coats of black tea and then the iron solution. Before finishing with a coat of the tea I waited until most of the surface moisture was absorbed into the wood.
- Walnut and Iron Solution: The same procedure as described above, only with the walnut solution instead of the tea.
- Black Tea, Walnut and Iron Solution: The last swatch is a mixture of all three solutions. I started with a coat of black tea. After this dried, I added a coat of walnut followed by the iron solution. After the application of the iron solution, I finished with black tea.
At this step, all the pieces look pretty dull but we are not done yet. I also noticed that the reaction of the tannins and the iron takes more than a few minutes and at the time I took the photo the swatches in the last row had not reached their final darkness.
Finishing With Linseed Oil
After giving the test swatches a few hours to dry completely I added a last coat of linseed oil. As you will see in the images below, this made a huge difference.
First of all the linseed oil slightly darkened the wood. This effect was strongest on the swatches in the bottom row. The linseed oil also removed all the dullness and brought the grain out very nicely.
Final Conclusion – Would I Ebonize Wood Again?
I did not achieve a 100 % deep, coal-black but overall I am very happy with the results. Originally I was just looking for a black stain but actually I also like the brown tones I got from using just the walnut and iron solution.
I was surprised how dark the final result of the black tea and iron mixture (swatch 5) became because the tea alone only very slightly darked the birch. The final color is a dark gray with a slight greenish tint.
The walnut and iron mix (swatch 6) is a dark brown with orange undertones. The combination of all three (swatch 7) gave me the darkest result. It is a very dark brown with golden undertones. I really like this color.