“Perseverare autem diabolicum” or thoughts on blackening Ash
In my last post I discussed the difficulty of trying to carve ash. Hey, don’t get me wrong. Ash is a wonderful material. Right now it’s plentiful and it’s cheap. It turns very well. And, properly finished, it is a very attractive wood that can be used (nearly) interchangeably with other ring porous species. But, as I recently testified, you’d have to be real masochist to want to carve it on a regular basis. Walnut or mahogany, it is not! You’re probably not going to see many highly carved pieces in ash.
Another real challenge with ash, is ebonizing it. Anyone who is familiar with this blog knows that I am keenly interested in traditional finishing methods. My ebonizing method of choice is iron and tannin. While this method gives absolutely beautiful results on walnut, mahogany, cherry and a host of other woods, using it on ash has always been a real challenge. In fact, I have “stooped” to the use of aniline dye and the “wiped, thinned paint” method on more than one occasion in the past. But after stumbling across an article by Brian Boggs on the subject, I decided I’d try it one more time; ergo: Preserverare autem diabolicum. (This is very similar to the definition of insanity being the act of repeating a behavior with the expectation of a different result.) The subject product is the coffee table I’m building for our living room. Hope it works (remembering that ash offers pretty good heating value).
Ash is not high in tannin so, following Boggs’ suggestion, I mixed up a batch of “oak bark tea”, 1 tbs/pint water. In this case, I used a bark powder product used in leather tanning. In the past, I’ve used oak bark, leaves and oak galls (which, I believe, have the highest concentration of tannin) to brew the tea. (I have heard of folks brewing a very “thick” tea from regular black tea, as well.) I brushed the surface of the table, liberally. The “tea” deepened the color of the ash after drying.
Next, I prepared a solution of iron acetate. This was made by simply soaking some steel wood in white vinegar for a couple of days. (Note: a gas is produced in this process, so don’t cork up the jar too tightly, lest you be injured by potential flying shards of glass. Put a rubber glove over the jar, or use a plastic container.) I’ve heard of other folks using iron (ferrous) sulfate which can probably be found in garden stores. What you’re looking for is iron to react with the tannic acid provided by the tannin tea.
I “decanted” the iron acetate mixture, through some cheese cloth and was left with a grayish, yellowish, greenish fluid, rich in iron.
Then I brushed the surface with the iron acetate solution, liberally. This is a messy process. So, unless you want black marks all over the floor, put down a dropcloth.
After this application had dried completely, I noticed the chemical process had not taken effect in certain areas of the surface. This was in the areas of the porous rings. (This is the problem when trying to ebonize ash.) I remembered that Boggs had said that he had put another coat of the “tea” on in order to get more tannin on the surface to react with any free iron. So, I figured that if one coat would help, two coats would work even better. I was sure that there would be plenty of tannin. After the second coat of tea was dry, I hit the table with another coat of iron acetate. I had my evening scotch, then went off to bed. When the morning arrived, I was startled by what I encountered. A deep brown precipitate had formed. (A light precipitate is normal, but grey or black not brown.)
It turns out that this was not a huge problem. After some light buffing with a “scotchbrite” pad, a lovely “warm” black color appeared. However, the area of the porous rings still had not been uniformly affected by the process. But with the judicious use of some “black oil” (lamp black in boiled linseed oil) a uniform look was achieved.
Three or four coats of rubbing varnish will produce a finish of incredible depth and durability.
So…what is the upshot of all this Alchemy? If you’re “into” historic finishing techniques, you’ll enjoy using this one. But as a commercial finish for anything made from ash, I’d have to recommend against it. What you’d save in product cost, is more than offset by the amount of labor involved. Any client who wants something built from ash will, very likely, not see the value of this finishing method. Use a thinned alkyd enamel or black milk paint, throw a couple of coats of oil or spirit varnish on it, and collect your payment. However…if you’re working with cherry or walnut and you need some ebonized surfaces…