Ebonizing describes two different methods. One is simply dyeing a wood black whilst the other is applying a chemical solution to blacken the wood. Both methods are only a surface finish and do not penetrate through the entire workpiece. An ebonized fingerboard may wear through after extensive playing.
When using the dye version of ebonizing, it is easiest to start with darker-colored woods. You can ebonize any wood, but a darker wood gets black more quickly. Additionally, closed-grain woods look more convincing than those with large open pores.
Mix up a fairly concentrated black aniline dye. Alcohol-based dyes dry quicker and do not raise the grain of the wood easily. Spirit-based products such as Fiebings Leather Dye work just as well as common wood dyes. Water-based dyes are also an option, however the water can cause problems with grain raising on some woods, requiring a plain water grain raise and knocking it back with fine sandpaper.
Brush a coat on the wood and let it set for about one-two hours. Take a rag and buff the wood to remove any excess that might have collected or sat anywhere. Feel the wood and check if any of the grain has risen. If so, knock it back with fine sandpaper.
Apply a second coat. When that's dry, simply buff the wood with clean clothes and finally apply a finish of some kind.
Not all woods can be reliably ebonized with this process, so test with a scrap piece if possible. Some woods turn odd colors which can be fun however we want them to go black! The woods that work most reliably with this method have a high tannic acid content. Woods like Oak and Walnut are ideal. Mahogany (Swietenia), Ash, Sycamore, Cherry, Maple, Pine and Beech also work, however they tend to turn varying shades of grey rather than black.
Firstly, we need to prepare our smelly chemical mixture. Take a handful of steel wool and rinse it with hot water and dish soap to get rid of any oils or contaminants. Stuff it into a glass jar and cover with white vinegar (acetic acid). Poke a couple of holes in the lid and screw that on before leaving the jar for a week or two, swirling the jar a little every couple of days.
The acetic acid in the vinegar reacts with the iron in the steel to produce iron acetate. What you'll see in the jar is a scummy rusted flaky junky mess swimming in a greyish liquid. This is perfect for our needs. The longer you leave the solution to work, the stronger the effects however a couple of weeks is good. Strain the liquid into a clean jar through a coffee filter and discard the junk.
To ebonize a wood, lightly brush on the iron acetate and watch as it reacts with the tannic acid in the wood and turns black before your very eyes! Walnut can turn a jet black within a minute whilst Oak can be variable with it being a lighter wood. The process may raise the grain slightly on the surface, so like the previous example be prepared to knock back any fuzzies with a bit of fine sandpaper and reapply.
If you wish, you can neutralize the acid by dabbing it with a cloth moistening with a sodium bicarbonate/water mix. This isn't hugely necessary unless you go a little too happy with the application. The fewer wet things you add the better.
To increase the reactivity of woods with lower tannic acid contents, you can make a tannin tea. Simply soak lots of tea and stew it to death. Strain through a coffee filter and use the resulting super-tea as a pre-treatment before the iron acetate. Don't leave this mixture for days however, since it will go mouldy very quickly!
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