Ebonizing oak

Paul and Stevie hollered on about the piano keys living in perfect harmony. Since ebony is VERY expensive, let’s make a cheaper wood very black using the ebonizing technique.

As a musician, I’d say P&S were wrong; not all notes go very well together. Unless you play jazz. I do not understand jazz, or at least the more esoteric variations. To quote the Dowager Countess of Grantham: “Do you think that any of them know what the others are playing?“. But then again, I am a simple mind. I understand gospel, blues, rock, country rock. French romantic and baroque too. And I do have a VERY good understanding of the 88 keys on my piano. Or the 183 keys and 32 pedals on my digital pipe organ. Anywhoo… – Ebonizing is new to me. Let’s do some research!

The principle

Some species of wood contains tannins / tannic acid in various amounts. Tannins react with iron, and that explains why leaving a hand plane on a piece of oak can result in black stains – in some cases, you’ll find small areas on freshly planed oak that turns a bit black, typically on high spots not yet taken down. Slam a nail in green oak, and over time you’ll get black staining around the nail. The chemical reaction between iron and tannin is what we are after. And we want that reaction to take place inside the wood, turning the wood itself black. As opposed to a stain which lays on the surface of the fibres, ebonizing turns the fibres themselves black. This is very good news for areas that may experience wear; ebonized wood will still be black after minor dents or damages. It is also very easy to repair, although a perfect color match may be difficult to achieve.

So why not just grab a a can of stain or paint? Well, stain and paint relies on pigments to work. In some way or another, you are covering the natural variations in the wood with a layer of pigments, and the color lies on top of the wood. Ebonizing using iron acetate is UV safe and the color changes take place inside the wood itself, on an molecular level. After the process, you can apply any finish you want. Oil, wax, poly lacquer…

We need to apply iron to the wood in a controllable way. By placing steel wool in vinegar, we make iron acetate. The steel wool is dissolved, and we can simply brush the liquid onto the wood. But there are pitfalls and things to do first, to ensure an even and repeatable result. And things we can do to encourage good results..

The witches’ brew

Google “witch brew” and click on google images. A suggestion pops up: “Starbucks frappuchino”. I don’t know what to make of that…

The recipe is simple:
into a vessel forged from plastic – the lid you must pierce,
place wool taken from sheep of steel with a force so fierce!
In with a stone to weigh it all down,
then pour in the vinegar – let them all drown!

Or in plain, non-halloweenish english: put some steel wool, washed and rinsed as there might be traces of oil from the manufacturing process left, into strong vinegar. 35% or so should do the trick – cleaning grade. Too weak vinegar (food grade) won’t yield any results, or at least very feeble results. Use a glass or plastic (plastic seems to be recommended, although I don’t really understand why) container with a pierced lid. The process releases hydrogen gas, and you want to vent that off – not contain it. Hindenburg and all that…

Tine Yoghurt buckets with screw-on lid. Really good packaging design!

Put a rock on top of the steel wool or wedge a stick somehow so that the wool stays submerged. We don’t want it to oxidize on us. Let it sit for a couple of days before you use it. The longer you wait, the more the steel wool dissolves. Before use, use a cloth or coffee filter to remove any larger bits of iron. You can also siphon off the liquid to avoid the sediments. The brew will keep for a long time, so don’t be afraid to make a good batch.

How much of each, you ask? It does not matter much. A good wad of wire wool – you can shred it and cut it to speed the process some – and cover it with vinegar. Drop in a stone to weigh it down. Leave it be for several days. The bubbles you’ll see forming is hydrogen. Since hydrogen is lighter than air, it’ll escape through the vent hole(s). Still – be careful. It ain’t called H-bomb for no reason! Don’t be a person one could describe as “did not invent the black powder, but I reckon stood awfully close when it went off”…

Another word of caution: use gloves, because vinegar at 35% concentration is an acid. Keep away from children and use caution. It will give you chemical burns!
Also, the iron acetate will turn your fingers black making it look like you’ve got your fingerprints recorded…

The mother of all tea brews – ebonizing kickstarter!

To give your wood a huge tannin boost – or to add tannins to woods that have none, such as pine – you can brew very strong black tea and apply it to the wood. And I do mean strong tea!

9 tea bags, forest fruit this time, into 3/4 liter of boiling water.

Don’t ever drink that stuff, your pupils will dilate worse than a cocaine addict enthusiast victim and you’ll spot leprechauns on the lawn! Even if you are born and raised on the Brennand farm in the UK, this is just too strong a brew! Use a tea with a fragrance you fancy, because your fingers will smell of it for hours. Trust me.

An alternative here is to make tea with oak shavings. Tannins are water soluble, and we want as much as possible of the stuff in the wood to get the results we are after. Chuck shavings, dust and scraps of oak into a bowl of water and let it simmer for a good while. Let it cool off (no need to remove the oak shavings at any point). Use the oak tea as is – no need to strain it. Wood is good.

Apply two to three liberal coats to the wood prior to applying the iron acetate (steel wool and vinegar) witch brew. You can apply more coats after the fact to deepen the effect. There is, however, no need to go overboard on the number of applications. At some point, you’ll wash off as much as you put on, and we only want it to become black – not completely vanta!

After the first coating, you’ve raised the grain. Sand, then repeat. You might have to do this several times until the grain won’t raise any more. Two birds with one stone, really, as you need to raise the grain anyway. You cannot do much cleanup afterwards, or you’ll take off the color – although a very light sanding with high grit is safe to do. Sanding after raising the grain will, to some extent, fill the pores in the wood with tannin-laden dust. This is a good thing, especially for porous woods like oak.

Loading the wood with tannins means that woods without any (or very little) tannic acid can be ebonized as well. Maple, pine…

Sanding does have another effect as it scuffs up the surface. This enables iron acetate (the vinegar brew) to penetrate deeper into the wood than if the surface is freshly planed. A planed surface is glassy smooth, and would lessen the effect. I got proof of this as the back side of my test piece, which was rough from the band saw, became pitch black within a minute, while the planed surface took a bit longer.

The reverse jacko

You know… going from light to dark in stead of the opposite direction, let us just leave it at that…

After applying the tea – if you choose to do so – it is time to make the transformation. Apply the vinegar / steel wool concoction to the wood and let the magic happen.

Do this in a well ventilated area or outdoors, as the fumes coming from the vinegar is disgusting! I do not know whether or not they are harmful, but anything that makes you cough should usually be avoided…

WARNING: Do not double-dip (safe-for-work-and-kids link)! Avoid contamination between the two brews. You’re not mixing paint here, you are doing alchemy chemistry (although with the price of ebony, I’d say alchemy is a pretty good choice of word!). You want the magic to happen inside the wood, not in the liquids.

Da-da-da-daaa… pesto! As Peanut would put it. Within minutes, the oak turns pitch black. You’ll be able to see the reaction happen almost immediately, and it will become darker and darker for quite some time. When dry, there might be a blueish tint to the wood at certain angles.

As for the picture above – it was VERY old oak, dry as a bone. It was red oak, too. Red oak has lower levels of tannic acid than white oak, thus giving a poorer reaction. The black strip was treated with tea before the vinegar solution was applied, and it yielded a much better result. The brown piece was not treated with the tea. Low on tannic acid and bone dry wood yields poor results. The brown “soot” could be brushed off, leaving a rather nice brown surface – if that’s what we was after.

I tried a piece of white oak I felled last year (dried to about 10% mc), and it became pitch black all on its own with no brown color. Sorry, no pictures…

After the vinegar has evaporated, you can add more tea to deepen the effect. You can also do the procedure once more if you want to.

The images above shows the effect on red oak. To the left, I am applying the first coat of tea. To the right, the result after three coats of tea, one coat of iron acetate solution and a last coat of tea. The brown “soot” was washed off with water, but can be seen in the pores. A light scrubbing with a nail brush improved this. Oil-based finish will further blacken the appearance. White oak would produce a much deeper black because of the higher tannin content.

After two application of tea and iron acetate, the above picture shows the result I ended up with on red oak. The image was taken before applying finish.

Finishing up

When you are satisfied with the result, you can give the piece a very light sanding (240 grit or above) to remove any raised grain. Wipe down with a damp cloth – it will turn black on ya, but it won’t remove the color from the wood. Use the tea in stead of water to give that extra little boost.

You can then apply any finish you want as if it was untreated wood.

Image source: The English Woodwoker, “The side table”.

The table on top shows ebonized legs with an Osmo wax oil finish – “it almost look like plastic, it’s so even”, to quote Richard. An article about building that table can be found here.

Richard Maguire, “The english woodworker”, has a great video series including plans for this table. I HIGHLY recommend the series (my table is built from his plans) – it is dirt cheap compared to all the information and knowledge you get access to. He charges a one time fee and you can download the videos for offline viewing. Go buy his series. You’ll not regret it!

– Now, how to complete the song and bleach wenge into ivory…?

Other sources for info on the topic:

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