Hi all,
I understand that some makers of box wood chanters give it the acid treatment to give it an antique patina.
Can anyone explain in detail how this is done please?
Thanks, Mike
Whilst I am sure there are various ways to acid stain/age a piece of Boxwood.. a search on the Web will usually provide infomation on any subject… here is a description of what I have done in the past. Word of warning; this is not for the faint hearted!!
Fume staining with Nitric Acid and Copper filings: 
Obtain a large glass container ( a fish tank with a glass lid would be good) long enough to take your pièces.
A wide based drinking glass or chemistry Beaker.
Purchase a bottle of undiluted Nitric Acid.
Make some Copper filings; old staples might do, or chop up an old Copper water heater cylinder.
Put the glass container somewhere out side, ( in your garden perhaps) not too near to your living spaces or near to other living things that you care about.
Place the beaker in the large glass container.
Using scrap sticks of wood to space your (finished) boxwood pièces off the base of the container and so’s they do not touch each other. Allow enough space between pièces so they do not touch each other. If you wish to treat a complete instrument then place all the pièces in to be fumed at the same time. Note that any waxes or oils should be cleaned from the Boxwood.
When all is clear and it is not a windy day, proceed to pour some Nitric Acid into the beaker… not too much and less than a quarter of the height of the glass beaker ( perhaps half a teacup’s Worth?).
Put the glass lid on the container leaving a gap so that you can drop the Copper Filings into the container.
The amount of Copper filings ( and amount of Acid) will have a bearing on the resulting colour produced. Perhaps the volume of the copper Filings should be about 20% of the volume of Acid… some experimenting should be done .
Now ,drop in the filings (gently, no splashes please) and quickly close the lid of your container and retire to a safe distance…
There will be a reaction and an Orange Gas given off which will impart a nice ancient looking colour to your Boxwood.
Leave the whole thing alone for an hour, then when the fumes are disipated the lid can be removed.
Here I Council you to use eye and hand protection of sufficient quality… do not get any Nitric acid on your skin!!! I burnt the end pad of my first finger right hand doing this 30 years ago and it still hurts!
Take out the Boxwood pieces and wash them in copious amounts of clean water… allow to dry slowly. There is probably something that can be used to neutralise any acid residue on the wood. Remember that because this is a fuming process there will be acid residue on the bores of the pièces too.
Dispose of any left over materials from this process.
Finish your Boxwood in any way you wish.
Good luck!!!
Geoff.
PS; I don’t do this anymore ! 
I have a vague memory od Sam Murray saying he neutralized with ammonia.. (doesn’t really add to the pleasant-ness of the whole operation, does it?) 
Hello Geoff.
I thank you for that informative procedure.
I have a couple of dumb questions. I’m not sure if I can produce that amount of copper filings although I’m sure I can locate a pipemaker or instrument maker who might be able to help out but I do have a couple of rolls of thin copper wire. Would this do if I chopped it up do you think? Final question is how do you dispose of the acid from the tank after use? My neighbours’ fish pond might make a suitable repository (only joking Steve, honestly). Seriously, how does one dispose of it?
Once again thank you.
Mike Delta
I just dipped a paintbrush with natural bristles into nitric acid of high dilution (that I bought from this local chemist´s, ~ 15 % = 15 parts acid 85 parts water), varnished the boxwood and let it dry outside. Got a nice honeyish colour. (see Geoff´s safety measures)
Acid-staining makes the darker stripes of the wood´s grain darker, whereas normal tan is especially soaked up by the softer, brighter parts of the grain and thus gives an awkward “negative” picture.
Chopped up copper wire might work but sometimes copper wire has a chemical film on it which may have to be cleaned (with household vinegar) but it may obscure the results.
I’ve used a pickle of apple cider vinegar and iron filings to darken rosewoods (including cocobola) haven’t tried it on boxwood though. I’ll try it on a scrap piece and let you know.
Tommy
varnished the boxwood and let it dry outside
Sunlight is an important ingredient in all these methods.
Tommy
Copper sheet or plumbing parts should be available at you local hardware store… you could ‘file’ a Copper elbow or bit of water pipe… you really don’t need a whole lot.
Clean up any residue with plenty of water (like at least 100 x the amount of Acid) and wash it down the drain… 
As I said, not for the faint hearted!
You could use some Hair Dye , a bit safer…
For safety’s sake I recommend a slightly different procedure, with dilute nitric acid and gentle heating with a heat gun. I find that this produces an excellent color, without the danger of splashing concentrated nitric acid, or the potentially even greater danger of nitrogen oxide fumes.
As Geoff says, there are of course numerous methods reported. I would stay away from the ‘fume cabinet’ methods because of the danger to the lungs, the red noxious gases in the box have to go somewhere when you are done.
I dilute the acid to about 25%, I think a chemist would refer to this as about ‘3 Molar’ but I am not certain. ALWAYS add acid to water, NEVER ADD WATER TO ACID as there is a serious, almost explosive spattering risk if you add water to concentrated acid. (BE SURE TO WEAR EYE PROTECTION for this and also the application below.)
Then I apply the dilute acid, sparingly, to the surface to be stained, preferably moving very slowly as on a rotisserie. I use a cotton swab on a stick for this (don’t use a plastic-stick Q-tip, the stick will melt in the heat). It pays to wear tight-fitting surgical latex gloves for this but it is not absolutely necessary. While still damp, gently heat with a heat gun or hair dryer in a well ventilated area. This blows the fumes away from you. At a certain temperature the color will suddenly develop; the reaction is exothermic thus it sort of comes on suddenly once it begins. Don’t overheat, touch up any missed spots gently and warm for a moment. Be sure to cover important nearby metal surfaces, and if the piece is chucked, clean the chuck afterwards.
You may then choose to neutralise the acid with dilute liquid ammonia solution. I prefer not to overwet the wood. Note that the ammonia is nearly more dangerous than the acid, and in my experience you can just wait and the acid will eventually self neutralise as the reaction proceeds to completion. The ammonia seems to result in a more neutral, less orange color and a slightly duller finish in my experience. Wet or soak the timber with linseed oil and leave it awhile, reapplying the oil as it soaks in. After a day or two you can switch to boiled linseed oil and use a small bit of garnet shellac to seal the pores. A rubbed oil-based finish looks best on the result in my opinion, but it’s very time-consuming.
Anyhow, that’s the way I do it these days. I don’t like the methods using dissolved iron, as .i think they are mixing a pigment stain into the equation which can be less uniform. Geoff do you have any comments?
- Bill
Sounds good to me Bill.
A much safer method all around and somewhat similar to Hans-Jorg’s treatment.
Though the Fume staining does do the insides too. Care would be needed (I would think) with this’ Painting it on the outside’ method so as to not make it look like a girl at the dancing compétitions with a Fake Tan… thinking of the insides of the finger holes and the bits of the bore that can be seen through them.
I always prefered women without the make-up… and the same for Wood.
Geoff.