"Ebonized" woods

[Tim Smith]

Some of you will be familiar with older instruments that have fingerboards and/or headstock overlays made of "ebonized" woods (often pearwood). I understand that the idea is to make relatively cheaper woods look like ebony. I have read that the process involves treating the base wood with nitric acid. Does anyone know more details about the process?

Of course, the nitric acid treatment yields wood that deteriorates over the years, often getting very brittle and exhibiting numerous shrinkage cracks. Some of it gets very friable, almost like soft chalk. I find this next to impossible to work with in rehabilitation of antique instruments (I stick to banjos). Has anyone some tips of working with this ill-treated wood? I have used cyanoacrylates but them don't seem to soak in very well, leaving a sort of haed shell.

In my former life I was a professional archaeologist and I know that curators treated delicate wooden specimens with a chemical called PEG (polyethylene glycol). It is a available in a variety of molecular weights. One the light end, it is a watery solution that soaks into the wood. The heavier ones are a hard wax-lke substance with preserves, stabilizes, and strenghtens the wood. Has anyone tried this substance on instruments?

Tim Smith
http://savethebanjos.com

[Vince Mondello]

Tim,
Like you I have used Cyano and it works well as far as fret slot strengthening, but not as a revitalizer of the board itself.
I know PEG is basically antifreeze with an additional polymer,and I can see it wicking in, as far as the stuff on the thin end of the spectrum.
I would wonder if the poly would cause it to have poor glue retention in areas saturated with.
Pearwood eats me up sometimes, it goes south on you pretty quick,
Vinnie

[Greg Mirken]

You can thin the CA with acetone, you know, for better penetration. The other problem with it is occasionally it'll turn white if it kicks off too quickly, so be careful about that.

Alternatively, you can use epoxy. I use West System epoxy and it's excellent stuff. Dries really hard without any rubberiness. I haven't used it for restoring spongy wood, but thinned slightly with acetone or MEK and warmed, it will also penetrate well.

Greg Mirken

[C Herb Hickman]

It sounds like two different questions.

I haven't heard of ebonizing with nitric acid, but it seems pretty clear the nitric acid (a strongly oxidizing acid) is being used to chemically char the wood, the char being black. I recall many years ago reading of a (then) old-timey staining method that used chromic acid (chromium trioxide), another strongly oxidizing acid. You probably couldn't do that today, as chromium compounds like that (hexavalent chromium) have been so demonized as carcinogens that you probably can't even lay hands on any, and it wouldn't do to leave a residue on a fretboard that shouldn't touch the bare skin.

It's not clear whether the deterioration with time is because the chemically charred wood is just not an enduring material, or is there possibly residual nitric acid remaining in the charred wood that continues to attack the structure of the wood. Today, there are several black stains that are used to "ebonize" wood and from what I hear black paints that are used for an even more fake "ebonizing." I have "Solar-Lux Stain Jet Black" from Grizzly which is a penetrating black stain -- have not made a comparison with the more expensive product from stewmac. This Solar-Lux has a reddish tinge which may or may not last.

Polyethylene Glycol I think came into use about 30 years ago, and the first attention I saw it get was in making things from green wood. It seems to me there was an article in Fine Woodworking, possibly 30 years ago. The PEG would soak into the green wood and fill the cell spaces permanently so that the wood cells did not shrink a lot on drying. I don't know of its being tried on instruments. It would add some weight and probably add no strength at all. But it might be a good idea for making dulcimers from uncured wood -- just a thought.