Sunday, September 4, 2016

Ebonizing Oak - An Experiment

On a hike last weekend in the Santa Cruz mountains that separate the San Francisco Bay from the Pacific Ocean, I came across this guy.
Banana slug
This one is about 4" long.  I don't see them nearly as much this time of year.  They're more commonly seen during the wet season.  OK, on to woodworking.

Richard McGuire's latest video series was a side table project that included ebonizing the legs as part of the finishing regimen.  If you haven't subscribed, it's an excellent series and I thought the part on ebonizing was well worth the cost of the entire series.  I thought I'd try the process on an oak frame that I built a couple weeks ago.

I have to say here - I tried to contact Richard and Helen to ask if they minded if I blog about my experiment, but I have not heard from them.  So I hope this is OK and if I leave out some details, you'll understand.

I started a couple weeks ago by preparing an iron solution that would be used to react with the tannins that occur naturally in oak to turn it black.
8-12 oz. mason jar, fine steel wool and some vinegar
I filled the jar with vinegar, put the lid on loosely (to let any evolved gases escape) and let it sit, stirring every day or two.
Just started
I didn't really know what to expect with this.  After two days it looked like this.  You can see a reddish brown muck starting to form at the top.  But the wool is dissolving.
After two days
I stirred it with a stick and got this.
After two days - mixed
I expected the solution to get black and stay that way, but it separates over a couple hours.
Day 4
Day 10
Here's what day 10 looked like from the top.
I ended up scooping out most of this muck
The second thing you need for the ebonizing is a solution that has some tannic acid in it.  Oak has tannins in it naturally, but apparently in dry oak (and this was very dry, old, re-purposed oak) the effect is less.  The answer is to take some oak shavings and boil them to create a tannic acid solution.
Mmmm, oak soup
When this was ready, I got the stuff together and hit the shop.  The following picture shows a pine/spruce/fir store-bought shim that I dunked first in the oak soup, then the iron solution.  You can see on the shim that I dunked about 2/3 of what you can see in the soup and after that, about 1/3 in the iron solution.  The oak soup has little effect on its own, but after the iron hits it, the color changes.
Testing the oak soup and iron solution on a coniferous shim
BTW, it's interesting that this worked on a wood other than oak that has no natural tannins.

After coating the frame with the soup and letting it sit a while (twice), I added the iron solution.  You can still easily see the original oak color, but the chemical reaction that turns things black keeps going well after the application of the solutions.
Oak frame (and scrap frame piece) after first application, shown with raw oak
Here it is after letting it dry.
After a while
I used one or two more applications to darken the color and after that was dry, I applied three coats of BLO with a day in between each coat to let dry.  After a few days curing, I applied a coat of paste wax and buffed with a shoe brush.
I like the color
I like how you can still see the grain.  The next picture is a close-up of one corner and you can see that I didn't get the solutions deep enough in the open areas of the porous sections of the oak.  I'm not concerned about that at all - it still looks really neat.
Close-up showing grain
On another section I took a picture with something in the shop that was black to get a comparison.
Not as black as this black plastic, but still pretty dark!
Another area showing hints of the original oak brown
I know I could have repeated the process a few more times (before oiling and waxing) to get a deeper black, but this was just an experiment.  So when I do this for real, I'll know what to look for and when I've gotten the color I want.

One last thing - I was interested in how far into the wood the black color reached.  So I took one of my scrap test pieces and crosscut it.  Here is the end grain view.  You can see a little penetration in the upper left where there was a small crack on the wood, but almost zero penetration from any long grain surface into the wood.
Shows almost no penetration of the color into the wood from long grain surfaces
And here is a view showing how far the penetration went into end grain.  Not even a 16th of an inch.  I expected a lot more.
End grain penetration
A nice experiment.  Next time I'll be much more liberal with my application of the solutions.  And once again - if you are interested in this method, think about subscribing to Richard McGuire's video series to get all the details.  He's really teaches well and I learned a lot from just this one series.


  1. Nice report on this. Richard got my attention with this ebonizing trick. BTW you can buy tannin from amazon but I like Richard's way better. I've also read that tea is a source for tannin.
    Did you mix the vinegars together or just use one? Richard's concoction looked different from yours. I'll have to watch it again and catch what vinegar he used.
    I like to cook and do you know vinegar has a 6 month or less shelf life?

    1. I used the distilled white vinegar, which was probably a few years old. Richard said that apple cider vinegar was used historically, but either will do fine. Interesting about the shelf life. I wouldn't have known that. Maybe I'd get better results with fresher vinegar. Six months?! Dang - I'd never use enough in that time. And who knows how long it's been sitting on the supermarket shelves!

  2. Hi Matt,
    great write up. I've seen this ebonizing trick at Tom Fidgen's videos a while ago. But I wasn't convinced by the result and he wasn't too and switch to a commercial stain.
    Richard's reults are much better and so are yours.
    I think the trick is the Oak soup.
    Maybe it will be an idea to filter the vinegar solution after it brewed for a few days.

    1. I thought about filtering. There's a bit of a "sludge" that collects at the bottom of the jar when the solution separates. I was worried that that was a lot of the iron. But I'm sure there is a lot of iron (atoms or ions) just in the vinegar. Maybe I'll try that next time.

  3. Great blog post.
    Popular Woodworking had an article about ebonizing some years ago.
    Brian Boggs uses Quebracho bark for the tannic acid source, but I like the idea of using oak though perhaps not quite as strong it is a chance that it is something that people have in their workshops.

    1. Wow, thanks for that article Jonas. I wish I read that before I experimented with ebonizing. I probably even have that article, but have no idea where the magazine is.