Tag Archives: Woodwork

Paint it Black?

So Rhiannon wanted a shelves and drawers thing to go under the stairs for her birthday, and her colour scheme is black. I agreed to make it, but I was not going to paint it, as I am in love with the patterns of the grain in any wood that I work with. However, while browsing Richard Maguire’s website,  http://www.theenglishwoodworker.com, my eye was caught by the design of his sidetable which has an undercarriage that is blackened via a process called “ebonising”.

Googling the internet showed that this process, which is several hundred years old, depends on the reaction between iron and tannin, shown by the black stain found around nails in oak, a wood rich in tannin. As it simply stains the wood, I hoped that it would still leave the grain visible, satisfying both Rhiannon and myself.

Many woods do not contain enough tannin for a satisfactory result, so the traditional recipe involves painting on a tannin solution followed by painting on a solution containing iron. The tannin solution is prepared by boiling up teabags and allowing them to stew, while the iron solution is made by dissolving steel wool in vinegar for a period of a week or more.

I experimented with this recipe, obtaining variable results, but then the inner chemist took over, and I ordered some tannic acid powder and ferrous sulphate crystals. Making up solutions from these with known concentrations, I embarked on a series of experiments which showed that it was very easy to ebonise wood after several coats of the two solutions.

Usually, the final colour had a bluish-purple tinge to it, but Rhiannon approved, so the SDT (shelves and drawers thing) became my first piece to be ebonised.

This, minus the drawers, was the SDT awaiting the finish, and I was happy with the joinery after planing and sanding everything smooth. I brushed on the tannin acid solution and left it to soak in for an hour, then started brushing on the ferrous sulphate solution.

The tannic acid wash gave very little colour change, but this is a few seconds after starting to brush on the iron sulphate solution. At this point, I was wishing that I hadn’t tried this ebonising thing, and was wondering how easy it would be to sand it off. However, a few hours later it had darkened considerably, as shown here, and a second application produced the usual dark black with a bluish tinge. I left it overnight to dry, and the next day I applied the final finish of danish oil. This immediately changed the colour to a more intense black, and the blue tinge was hardly detectable.Satisfied with this, I ebonised the back of the SDT and the outside of the two drawers with two applications of the tannin and ferrous sulphate solution, and finished them with danish oil as well.

Here is the completed SDT, together with sunlight, in our conservatory.

I delivered the piece to the client, who seemed pleased, and here it is in situ.

There are a number of blogs by woodworkers around the net, describing how they have investigated the best way of using this technique, and the suitability of different types of wood. Conclusions have been drawn, some of which I do not believe are correct, as they vary. I think the chemical reactions by which the black substance is formed is very complex, and I am going to throw another factor into the mix which I do not think has been remarked upon previously.

I believe that as the two solutions get older, the time taken for the wood to darken gets less. I think that this is true, due to my observations over the several days that I ebonised the SDT, then the back, then the two drawers. If this is indeed true, I have a possible explanation, from my background in chemistry.

Here goes – iron compounds can exist in two forms, ferrous and ferric (different valencies – look it up if you must). Ferrous compounds are less stable, and tend to react with oxygen in the air and become the equivalent ferric compound.

Perhaps it is ferric compounds which do the ebonising reaction with tannin, and ferrous compounds are incapable of doing so. This would explain the comparative slowness of reaction with freshly made up ferrous sulphate solution – it would have to react with oxygen in the air before it could react with the tannin. After a few days, most of the ferrous sulphate would have been oxidised to ferric sulphate, hence the speed of the colour change when doing the drawers.

There are too many other interesting things to do for me to take this any further just now – next time I want to ebonise a project, I’ll check out whether my observations are repeatable, but the important thing to me is that it works!

An old carpenter’s bequest

We are in Dunedin, sharing Christmas and the New Zealand summer with Sue and Pete and the grandsons, Tarren and Bryn. In the garage back home is a stack of sycamore planks and beams, freshly milled from a tree felled in our wood, levelled and sticked to enable them to dry with minimum bend and twist. They are destined to become a garden bench for Carol and Ian, and a solid, heavy workbench for me – after a lifetime of DIY using a Black & Decker Workmate, I am going to have a proper workbench at last.

Having been researching bench fittings and accessories for a while, I have become sensitised to such things, and a few days ago, I noticed a newly interesting device attached to the ancient, mouldering workbench in the garage.


I say “newly interesting” because we have been visiting since 2002, and I haven’t noticed it before. I’m talking about that plank of wood attached to the bench by a threaded rod (not visible) and a tommy bar. Obviously a vice of some sort which had been very well used in the past (not recently though, eh Pete?) judging by the wear the wood had suffered.

Researching what kind of vice it could be, I got no help from Wikipedia, which listed a number of different vices, none of which could be the one in question. It was only when I delved into the world of woodworking forums (fora?) that I came across the staple of 18th century carpentry, the leg vice. Apparently, this device was ubiquitous at the time, and fell into disuse with the arrival of the mass produced iron face vice, but is now making a bit of a comeback – see this link to a modern manufacturer with some improvements to the original design. The leg vice had a guide attached to the bottom of the plank in order to keep it parallel to the leg, and I then noticed the rectangular hole near the bottom of the plank by which the guide would have been attached. And, conclusive confirmation, when I felt the leg supporting the bench, there was the hole that the guide would have passed through.

I was immediately captivated by the idea of incorporating the leg vice, with its long history and working life, into my new soon-to-be-built workbench. When I told Pete about my discovery and diffidently suggested that he might like to refurbish the leg vice, he pointed out that he would not use it, and immediately set about taking it apart. After overcoming a reluctant screw, we soon had the vice screw and the threaded socket in the bench leg removed.

20141217-080836 The ironmongery is all I shall take home – hopefully, it will not send my luggage allowance over the limit – and the plank of wood, technically called the “chop”, will be replaced by a brand new piece of sycamore from our wood. Oh, and I’ve bought Pete a Workmate for Christmas. Perhaps Bryn might get some use from it …

So what was the leg vice used for? It is particularly good at holding large items such as doors or window frames. Sue tells me that all of the houses in her street were built by the same chap, and it seems possible that at least some of the fittings for the houses were prepared on it.

If you want to know more, an English improvement on the old leg vice is here, and the story of someone else who refurbished a leg vice family heirloom is here.