My Black Wattle Woodpile – The Gift That Keeps On Giving

When it was really cold in September I ran out of firewood. Bad planning on my part – especially since all the local firewood suppliers were flat out of stock at the end of winter. Finally I got hold of somebody who had some freshly cut black wattle wood. In my desperation I decided to make other plans for any short term needs and buy the wet black wattle with the view to stack it and dry it here at home.

Acacia mearnsii

Of all the wood that grows locally, black wattle (Acacia mearnsii) and rooikrans (Acacia cyclops) is the most favoured ‘braai’ or barbecue wood. Black wattle is very hard, burns hot and slow, and makes long-lasting barbecue coals. Black wattle is indigenous to Australia but was introduced in South Africa in the 1850s. Since then it has been cultivated on a large scale, primarily for tannin. It spreads readily from seed and is also considered a highly invasive alien plant threatening indigenous vegetation. Today black wattles in the wild are kept in check by encouraging the spread of the Black wattle gall midge (Dasineura rubiformis). The midge produces galls in the flowers effectively preventing seeds from developing.

“It’s green, ay,” the wood supplier said, and I thought they meant that figuratively. But when my 500 pieces of freshly cut black wattle wood arrived the bark was quite literally bright green. I now had a big stack of wet firewood that was useless for making fires any time soon. However, it turned out to be useful for a whole row of other things.

Green Wood Carving

As I was looking at the freshly stacked wood on the first day I suddenly realized I had a treasure trove of whittling wood right there in front of me! Among whittlers green wood carving is very much a thing. Freshly cut wood has a high water content making it nice and soft to work with. Once the wood dries it hardens and becomes more taxing to carve – both on your muscles and your hand tools. Black wattle timber has a Janka hardness of 1710 making it almost as hard as merbau, African padauk, or apple wood and well harder than e.g. oak. Once it’s fully dry it becomes difficult to carve with a knife.

My first black wattle project was a whittled hand distaff with a goose motif.

A distaff is a stick that you tie the fibre (typically wool or flax) to when you spin yarn. Spinners have used distaffs for millennia and distaffs are quite possibly the historical precursors of the ‘magic wands’ of Harry Potter and other modern day magicians. The goose motif was a popular adornment on distaffs in Roman times. The goose represented the goddess Juno who was connected with all aspects of the life of women – spinning included.

That bright green bark looked fascinating and as I was working with the wood I did some research on black wattle. Turns out that black wattle bark is a great source of tannin. Tannins are polyphenols; bitter-tasting, astringent phenolic compounds that plants use to protect themselves.  Tannins protect fruit from being eaten before it ripens and they protect the plant from bacterial and fungal attacks. Tannins are strong antioxidants and they bond with metal ions, i.e. they work as chelating agents. They are called tannins because they have been used for leather tanning since forever.

Ebonising

Woodworkers use tannins and iron to stain wood in a process called ‘ebonising’. Like the name suggests ebonising turns the wood very dark or black – like ebony. The way to do this is to introduce tannins (either present in the wood or added separately) to an iron solution resulting in black colour.

Given that I now had an ample supply of tannin-rich bark in my woodpile I wanted to see if I could ebonise something.

I made an iron acetate solution by first carefully washing the oil out of some fine steel wool from the supermarket. I put the washed steel wool in a mason jar and poured white vinegar over to cover – and a bit. The steel wool and vinegar started reacting immediately with plenty of tiny bubbles continuously rising to the surface. I made sure not to tighten the lid on my jar in order to let the gas out.

Many tutorials said the solution needed to stand for a week or two, but being impatient and encouraged by all the tiny bubbles I decided to test my iron acetate solution after a couple of hours. And I was richly rewarded; on the tannin-rich inner bark of one of my black wattle logs a couple of brush strokes of fresh iron acetate became a rich blueish black.

How cool is that?! Nothing like a bit of backyard chemistry!

This clearly deserved a bit more exploration. I stripped the bark off a couple of logs, tore it into fine strips, simmered it in water for several hours, and let it stand for 24h. Then I filtered it and now I had a strong black wattle tannin solution in addition to my iron solution – which incidentally both had much the same transparent amber colour.

With the additional tannin of the tannin solution I was able to make a dark, intense stain on wood. By brushing on and alternate coats of tannin and iron and letting them dry in between I made a piece of light oak wood very dark. Once I felt it was dark enough I burnished the piece with a polished gem stone. Now it looks like something that might have been lying in a bog for a few millennia.

I also ebonised a crochet hook that I whittled from my black wattle wood. A whittled black black wattle hook.

Black Wattle Tannin Mordant

Tannins are often used as mordants (substances helping dyes to chemically bond to fibres) in textile dyeing. With my tannin solution I mordanted some wool yarn (I put the yarn in the pot while I was simmering the tannin solution). I then added some iron solution to the tannin soaked yarn which turned a nice dark grayish brown. A word of caution here: the tannin/iron colour is both lightfast and permanent, i.e. you want to be careful not to get any of it on your clothes, shoes or any other unintended surfaces.

Leather Dye

I also tested my two solutions on some scrap leather. The piece on the left is ‘wet blue’, undyed, chrome tanned leather. The piece on the right is vegetable tanned leather.

At the very left is one brush stroke of iron solution. On the leather that has not been tannin treated it just has its own slightly rusty colour. To the right of that is an area that was first given a coating of tannin solution and then a coating of iron solution on top of that. The permanent deep grey is fairly impressive. But most impressive is the one brush stroke of iron solution on the vegetable tanned leather to the right. The the iron instantly turns the residual tannins from the tanning process a rich blueish black.

In cosmetics condensed tannins like the ones in Acacia mearnsii bark have astingent and anti-inflammatory properties and they are beneficial as antioxidants and as chelating agents. They are fungal and bacterial inhibitors and form a poor breeding ground e.g. for bacteria causing body odour. High quality leather shoes are usually lined with tannin processed leather where the tannins help keep the shoes from becoming smelly. Tannins are highly astringent and diminish skin pores by contracting them. Tannins are used as mordants in natural hair dyes and are used for hair straightening, hair smoothing and anti-frizz treatments.

Soap Colourant

I was on a roll with my black wattle tannin extract solution and I obviously wanted to test it in soap too. As always soap is a rinse-off product spending a very short time on the skin. To expect soap to impart long-lasting and far-reaching effects on the skin beyond gentle cleansing is usually misguided. However, the antioxidant polyphenols may well lengthen the shelf life of unsaponified oil in soap keeping it from going rancid. The chelating properties of tannins may also help reduce soap scum.

For my test batch I decided not to be shy but to do a full water replacement with my amber-coloured black wattle tannin solution. With liquid at 20% of oil weight I figured I might not see much colour once saponification was complete. After all it looked very much like strong black tea which doesn’t impart much colour in soap. Lo and behold how wrong I was.

As soon as the sodiumhydroxide hit the tannin solution it turned an intense dark brown. When the soap was in the moulds it looked darker than any activated charcoal or pine tar soap I’ve ever made. The fully saponified soap is very dark and when you wet the soap the colour is almost more of a blackish red than a brown. Very striking. The lather is close to white, but the colour does run slightly. For future reference a more diluted solution will be fine.. If you don’t have access to black wattle bark like I do you can buy Acacia mearnsii tannin as a powder. It’s likely that a solution made from powder is going to be much lighter than my infusion which was simmered at length, green rind and all.

Black Wattle Ink

Finally I used my black wattle tannin solution and iron acetate for something I’ve been wanting to try for ages. I made beautiful permanent ink.

A traditional recipe for ink calls for oak galls aka apple galls which are exceptionally rich in tannin. Like black wattle galls oak galls are caused by insects. But I’ve never seen an oak gall so I assume we don’t have a lot of oak gall wasps in this area even though oak trees are very common here. In addition to oak galls the recipe calls for iron and some gum arabic to increase the surface tension of the liquid and provide adhesion.

Gum arabic is edible, water soluble sap from a variety of acacia species. In my neighbourhood there’s a sweet thorn aka Vachellia karroo (an indigenous tree formerly known as Acacia karroo) that produces beautiful drops of gum arabic – which sometimes end up in my pocket.

I had tannin solution, I had iron solution and I had some chunks of foraged gum arabic. I added some of each to a pot, reduced the liquid by boiling – and ended up with permanent ink.

Never mind my wonky lettering – the ink works perfectly. It flows nicely off the dip pen nib and stays where it’s meant to stay. Once dry this ink is permanent – a drop of water does nothing to wash the letters away. And Shakespeare’s sonnet is forever gold…

Who’d a thunk that a pile of wood could be so much fun. And come February I might actually be able to use it to fire up a ‘lekka braai’ for my birthday.