I am making a small walnut cabinet, and I want to use Baltic birch plywood for the shelves. In order to darken the plywood to complement the walnut sides and frame I could paint, stain, or ebonize the plywood. I have never tried the old fashioned ebonizing technique using steel wool and vinegar, so I decided to give it a try; with some experimentation along the way.

The widely available recipes on the Internet call for making an iron acetate solution from steel wool and vinegar. This will create a nice dark tone on wood with a high tannin content, like oak, cedar, walnut and some mahoganies. Unfortunately birch, and thus Baltic birch plywood has lower tannin content, so you have to add tannin to the wood fibers to create darker tones. You can use a tannin solution made from black tea, from Quebracho extract, or from high tannin wood shavings.

One thing to remember is that the ebonizing technique penetrates the color into the wood fibers, so a certain amount of sanding afterwards will not take off the finish. The downside of that, or maybe more of a caution, is that you cannot achieve a defined sharp line between the ebonized and the untreated surface: the stain will bleed into the adjacent wood fibers even if you tape the area off.

Here is the recipe and the variations I used.

Iron acetate solution made from steel wool and cleaning-grade vinegar (Step 1)
Tannin solution from walnut shavings/sawdust (Step 2)
Tannin solution from super strong black tea [don’t drink it :-)] (Step 3)
A solution of turmeric powder in water to add a warmer tone to the stain

Supplies

Cleaning-grade vinegar

Superfine (0000) steel wool

Black tea

Walnut shavings/sawdust

Turmeric powder (for warmer tones)

1 qt containers with lids, paint brushes

Step 1: Make the Iron Acetate Solution

I used three pads of super fine (0000) steel wool. I washed the steel wool with dish soap and rinsed with water to remove any oil coating. The steel wool pads were torn to pieces, put into a one quart plastic container, and submerged in cleaning-strength vinegar. To keep the steel wool below the liquid level I weighed it down with a couple of rocks. You don't want the steel wool above the liquid level as that would produce rust and contaminate the iron acetate. The container was covered with a lid. Small holes in the lid let the produced gas escape; be sure to do that! Then set the container aside for a week or so, checking and stirring it occasionally.

After a few days to a week some of the steel wool has dissolved and the container/liquid looks pretty nasty. I strained the solution through a piece of t-shirt fabric. Surprisingly, the solution is clear.

A word of caution: The iron acetate solution stains everything, including your fingers and your clothes, so wear gloves and an old t-shirt. You also want be careful in your shop: I accidentally and permanently speckled my home-build Moxon vise - last picture above!

Step 2: Make the Tannin Solution From Walnut Shavings

I had a bunch of walnut chips and shavings from the cabinet project I’m working on. These came from jointing the walnut boards for the cabinet. Perfect, walnut has a high tannin content! The shavings were put in a bowl, and boiling water was added to fill the bowl. I let it sit for one day, stirring occasionally. I then drained/strained the solution thru a t-shirt and a coffee filter to remove the solids. Let's call it walnut juice!

Step 3: Make a Tannin Solution From Black Tea

Make a strong black tea. I used 8 tea bags in a cup and let it steep for an hour. I did not taste the tea :-)

Step 4: Making Test Samples

I cut eight 2" by 2" tiles from the Baltic birch plywood and lightly sanded the surface with 220 grit. During some initial testing I noticed a distinct gray to purple tint in the samples. This is ok if you want to achieve a weathered look, but I was aiming for a warmer tone. I decided to try a turmeric solution along with the tannins. Two tsp of turmeric powder in 2 oz of hot water. The first picture above shows a tile with walnut juice, black tea, and turmeric (L to R).

I also used a drop of dish soap in each solution to break the surface tension and help with penetrating the wood fibers.

Each sample was prepared by following these steps:

Apply the tannin solution (walnut or tea), let dry, apply the turmeric solution (samples 4 to 8 only), let dry, apply the iron acetate solution, let dry; indicated below as 1x. Repeat the same steps (shown as 2x).

After becoming fully dry overnight the samples were finished with one coat of water based polyurethane.

Sample 1
Iron acetate only: 1x left half, 2x right half
Sample 2
Walnut juice, iron acetate: 1x left half, 2x right half
Sample 3
Black tea, iron acetate: 1x left half, 2x right half
Sample 4
Black tea, turmeric, iron acetate: 1x left half, 2x right half
Sample 5
Turmeric, iron acetate: 1x
Sample 6
Turmeric, iron acetate: 2x
Sample 7
Black tea, turmeric, iron acetate: 2x
Sample 8
Black tea, turmeric, iron acetate: 3x

Step 5: Results

It is hard to accurately present the colors in these pictures. So here are my personal observations and preferences regarding my ebonizing treatment of Baltic birch plywood.

You can achieve a near black finish with black tea, turmeric, and iron acetate applied 2 or 3 times, samples 7 and 8. There is very little difference between 2x and 3x; but 3x appears slightly darker and would be my choice for 'black'. I don't believe that 4x application would make a noticeable difference; maybe a stronger iron acetate solution would. My wife calls samples 7 and 8 dark brown.
The color change takes a while after first applying the iron acetate. Be patient, wait an hour or more. The second picture above shows sample 5 after turmeric solution has dried, five minutes after iron acetate application, and 1.5 hours later.
The satin polyurethane coat at the end deepens the color. An oil-based finish would probably do even more to bring out the tones.
The turmeric solution does warm the tone in lighter finishes like sample 5 and 6, but is a little bit too yellow for my taste. Use sparingly.
The turmeric solution appears to make the darker samples 4, 7, and 8 more black than dark purple. Without the turmeric the final color can have a dark purple tint.
For the lighter finishes different parts of the plywood surface have slightly different tints.
A surface scratch that looks bad while the iron acetate is still wet may miraculously disappear when dry, see pictures 3, 4, and 5 above.
For my walnut shelf project I ended up liking a lighter finish. I used sample 2: walnut juice, iron acetate, 2x.
The last picture above shows the completed shelves in the not-yet completed cabinet.

What I don't know at this time is how long the iron acetate, tea, and walnut juice solutions will last in a jar or bottle, i.e. if you can store them for later use. Their chemistry may change, the iron acetate may precipitate out, the walnut juice and tea may mold, etc. I'll try to remember to update this Instructable a few months down the road!