how to turn oak black

[beaumontnz]

some years ago i was watching one of the many design programs on tv where they were building something out of oak.
As a finish, they applied something to it which was not stain,but maybe some kind of acid(?),and it turned the oak purple/black, and it looked really good,(and cheap!)
I fancy using this technique for a little project in oak,anyone know what this stuff is?

 

[Deleted member 174758]

Basic chemistry, really. Oak contains tannin. Tannin plus water creates tannic acid. Tannic acid plus iron makes black iron oxide.

One traditional recipe was to soak iron nails in vinegar for a month or two which creates a blue/black "brew" which can then be applied to timber. The process can be speeded up considerably by using fine wire wool instead of nails - to about 2 or 3 weeks. The resulting potion, strained off through several layers of butter muslin and then applied with a lint-free cotton cloth, will blacken oak (BTW wear rubber gloves!). Several treatments may be required to reach the desired hue. This is a very traditional method of ebonising and has been used for centuries

Oak, walnut, cherry, real mahogany (i.e. South American, not African species) and many exotics are good candidates because they already contain tannin. If you pre-treat wood with a solution of tannic acid or a liquid containing tannin (cold, very stewed tea works), it will ebonise almost any timber species.

After use, seal the surface with a clear sanding sealer or bleached blond shellac polish (so called "white" French polish) before finishing

 

[getitdone]

Or let someone else do the chemistry - Scroll down to the reactive stains here:
http://www.ciranova.be/media/files/Kleuren_Colors_Couleurs_Ciranova_2013_1371025750.pdf

and look at the black. I've used it a fair bit and always get good results. You could then use a black hard waxoil to finish it and make it even darker, or a clear hard waxoil if the reactive stain is dark enough.

The reactive stain is just that and offers no protective properties, hence the need to cover with a hard waxoil or similar. Other manufacturers (if you struggle to locate a stockist of Ciranova) of good black-pigmented hard waxoils are Osmo or Treatex which can be easier to find.

I think Rustins also make reactive stains, but I haven't used them so can't comment on their results.

 

[Gerrydelasel]

Another tranditional forumla was Van Dyck walnut crystals. 100g in a couple of litres of water makes a very deep brown, almost black.

But then, black wood dye is one of the cheaper colours you can buy. Quick, easy, done.

 

[ladylola]

Another method that turns the oak a range of colours from red to dark brown and is cheap is lime water. I was first shown this method years ago and have used it many times . I've done it with hydrated lime but using unslaked seems to work better. Simply slake up the lime i.e. add water to it , it will heat up , an exothermic reaction calcium oxide and water gives calcium hydroxide or caustic soda so protective gloves etc are needed. Then "paint" on the resulting liquid . Colours can vary depending on the oak but quick and cheap.

 

[beaumontnz]

Well the strong tea did not work, the cost of tannic acid is the same- is as stain so I might try some caustic soda as I have some.
Failing that I'll just buy some stain.

 

[Deleted member 174758]

Well the strong tea did not work, the cost of tannic acid is the same- is as stain so I might try some caustic soda as I have some.

Please re-read my original response. You have absolutely no need to buy tannic acid at all because you already have oak - and oak contains tannin. What you need to do is to provide something to extract some of that tanin and turn it into tannic acid, something which also contains dissolved iron which the tannic can react with to create ferric oxide - the black stain you require. That something is steel wool left to soak in vinegar for several weeks. Cheap as chips. The cold tea isn't a stain at all (again stated in my previous response) - it is a way to provide tannin which the vinegar and steel wool brew can react with, it is NOT a stain in itself - I specifically stated "PRE-TREATED"

I'd be wary of messing with caustic soda, though, it can be extremely volatile

 

[ladylola]

It's true that working with slaked lime water requires a degree of care , rubber gloves and goggles to protect from splashes but it does make a cheap and efficient method of blackening on a large scale such as a building. Stockholm tar was another product commonly used at one time on building timbers which by its very nature is also black.
Re reading your original post I see you mention a small project. It may perhaps be as well to avoid all the faffing around and just use something like Colron Tudor black wood stain , easy , cheap enough and straight out of the tin.

 

[beaumontnz]

Any particular kind of vinegar?

 

[ladylola]

Normally use distilled vinegar , the clear sort . Regular vinegar , the sort you put on your chips , sometimes has caramel added for colour so better to start with something simple . Either way a bottle of distilled vinegar is always a good thing to keep as it has so many other uses around the home.

 

[beaumontnz]

Should I expect this solution to change colour then?,as the vinegar is clear,as it isn't currently doing so after a week.

 

[Gerrydelasel]

Should I expect this solution to change colour then?,as the vinegar is clear,as it isn't currently doing so after a week.

There are LOADS of tutorials about this on the internet:
http://www.apieceofrainbow.com/make-wood-stain/

 

[beaumontnz]

just a thought.....
does the age of the oak make any difference,as mines is probably 30-40 years old?

 

[ladylola]

In my experience yes. Green or semi green oak will react much more with lime or vinegar than seasoned oak.

 

[beaumontnz]

Result!
vinegar finally worked.
thanks to all posters.
on a final note,with regard to the finish,out of the options listed by other posters,which would best give a satin sheen? I have tried a acrylic varnish but it did not work well,and i have no experience with waxes or shellac.