Verdigris

Irish Flute
1

Verdigris. The Green of Greece. Or more scientifically, a green or bluish deposit especially of copper carbonates formed on copper, brass, or bronze surfaces.

I don’t spend much time in the presence of Verdigris, but I spent the greatest part of today there. And I’m wondering if anyone can explain why.

I’d been sent a flute for repair made here in Australia probably in the 80’s. Boxwood, partly stained. Five keys (no Long F though it has the blocks). Brass rings, brass keys and brass tuning slides.

An immediately obvious issue was how slowly the keys were to return when opened. Indeed, the c key hardly bothered. Other issues included the head and barrel slide being immovable, and the cap similarly stuck.

When I got the keys off (and that was quite an effort), I found the slots and key were covered in Verdigris. Ditto the key pin holes.

I used the hot poker trick to separate the stuck tuning slides. Again, with very great difficulty. I had to call a son in to help rotate the slide and pull it off. The overlap area of the slides choked with Verdigris. And extending up into the cavity at the end of the head where the barrel slide hides. Didn’t help that the maker had made the clearance there very small. Mutter, grumble, mutter grumble…

And when I got the cap off (with much difficulty), the surface of the cap and the thread that secures us was covered in, yes, you guessed it, Verdigris.

And so then I pushed the cork stopper out. Again with much difficulty. And guess what it was caked in…

Now, have I just lived a charmed life, and the rest of you typically spend your days scraping Verdigris off stuff? Or is it enough that this flute makes extensive use of brass to explain why it was so afflicted? Or does it suggest to us that maybe it had spent a lot of its life in a very damp climate? (I haven’t followed that up with the owner, but I will.)

I even wondered if the staining on the boxwood was done with nitric acid, and that the maker had neutralised the acid with vinegar. A bit too much vinegar? Another definition of Verdigris is: a green or greenish-blue poisonous pigment resulting from the action of acetic acid on copper and consisting of one or more basic copper acetates. I’m a bit hesitant to go down that path because, while the body parts appear stained, the head is less stained, and the barrel appears unstained. And yet the Verdigris is everywhere. But who knows?

The good news is that, despite the risky and difficult procedures it had to endure today, the flute is well on its way to recovery. I’d feel better though if I could explain the presence of so much Verdigris spread so much throughout the instrument. And give the owner some advice as to what to do to keep it at bay!

Anyone?

2

My late uncle was a member of a colliery brass band. One of his jobs was looking after the loan pool, a collection of instruments they kept for people who were interested in learning but didn’t yet have their own, and he had a lot of trouble with verdigris in some of them.

He reckoned it was partly because some alloys are much more prone to it than others, partly because instruments would be played, not cleaned very well, and then stored for comparatively long periods, and partly because of chemical differences in what individual players breathe out.

That was his three ha’pence, anyway. As for individual quirks: my skin quickly removes the finish from computer keys and I once worked with someone who killed digital watches and photocopier controls with static, so it wouldn’t surprise me if something similar is possible with breath and verdigris. :laughing:



Edit: Just remembered my uncle once told me about a problem that affected some high-class pianos. At one stage the manufacturer used a metal that was really prone to verdigris, leaving owners with huge bills to rectify it. I can’t remember the details, but it doesn’t sound like a simple case of cheap materials and poor storage conditions.

3

Yeah, I wondered if the alloy has something to do with it. The wide flat rings on this flute are quite bright, and don’t show signs of Verdigris. The slides were jammed with the stuff, and the cap and the stopper too, yet the head liner (which becomes the inner slide) on both sides of the stopper was fine. The keys are dark with oxide, with traces of Verdigris. Where I’ve removed the Verdigris, which is where they went through the blocks, the keys are now bright. So it seems the Verdigris mostly forms where other materials are in contact with the brass.

And I could understand if it’s due to the breath, but the breath can’t get to the surface of the stopper or cap, or the gaps between keys and their blocks. So it’s not that.

Oh, and stupid me, talking above about neutralising nitric acid with vinegar. Vinegar is an acid - you would need a base to neutralise nitric acid. So ignore that notion!

Flute is playing very nicely this morning. This is one of the rewards for the flute restorer!

4

If it’s a modern flute a few decades old, maybe the brass had some kind of coating on it that’s now broken down?

Anyway, if it is the makeup of the alloy, verdigris is likely to carry on developing and the owner will need to keep an eye on it. It’ll be much easier to maintain now you’ve got rid of years of accumulation though.

5

Brass is normally considered as a pretty stable metal not requiring a coating to prevent corrosion. It will oxidise, but that thin layer of oxide then acts as a protective surface. In the case of this flute, I think the dark colour of the keys is the oxide. But it is interesting that even on the keys, there are some signs of Verdigris. Pretty negligible though. It’s in the spaces between wood, thread or cork and metal that the Verdigris forms agressively.

My understanding is that Verdigris needs moisture and air to form. But how would the outside of a flute suffer so much moisture? Or inaccessible areas like the cavity between cap and stopper?

I recently had a visit from an old flute playing colleague, who had since gone to live in Malaysia. He reported that extreme RH levels were pretty normal. Perhaps our poor flute had been summering in the Malaysian highlands. Humidity there approaches 90%.

Argghh, not for me. I was designed for Ireland!

6

Perhaps our poor flute had been summering in the Malaysian highlands. Humidity there approaches 90%.

Argghh, not for me. I was designed for Ireland!

FWIW, RH in Clare is currently well into the nineties, albeit at a temperature of 15 C.

7

I tried looking up what my late uncle once said about pianos, and it turns out the maker was Steinway. Some of their instruments clearly developed it without anyone huffing moisture-laden air through them, so maybe that isn’t the underlying cause?

8

I have encountered a lot of verdigris working on antique flutes. Some have a lot more than others. My understanding is that it is basically the result of corrosion of metals such as brass and nickel silver / German silver, that have a high copper content.
The amount of verdigris is probably related to the atmospheric conditions in which the flute has spent most of its life. If it has lived in a smoggy environment, and been exposed to a lot of sulphur dioxide, say, then I would expect it to have a lot more verdigris than a flute that has lived in a cleaner environment/atmosphere. The acids that cause the corrosion do not necessarily come from the player.

9

Yeah, I’ve certainly come across it, but never in this quantity. This stuff is caked on, filling every cavity.

It’s a greenish colour, so I’m guessing copper carbonate, rather than copper sulphate which would be more blue. So, I’m thinking it’s more moisture than pollution. But I still wonder how it gets into sealed places like the cap and the stopper. Hmmmm…

Most of the 19th century flutes seem to have nickel-plated slides, rather than plain brass. I wonder if that was to ward off Verdigris?

Military flutes back in the 19th century were boxwood with brass fittings. Cheap. I wonder if they were plagued by Verdigris?

I’m reminded of the old joke…

The Colonel enters the barracks and sees a new recruit laboriously trying to polish his brass belt buckle. “So, tell me, Private, what is brass for?”
The Private jumps to his feet, salutes and blurts out: “For the polishing of, by troops, Suh!”

Interesting, Mr Gumby about the high humidity in Clare. Not far from the sea I guess.

10

Interesting, Mr Gumby about the high humidity in Clare. Not far from the sea I guess.

I doubt it will be much different in the Midlands eventhough the West is usually more humid than the east coast. My point was, obviously, that your ‘I was made for Ireland’ appears to underestimate the average humidity here.

This time of year is usually very humid but RH is high the year round. It can fluctuate, depending on the airmass we find ourselves in, southern winds usually bringing very humid, warm air from the southern Atlantic. We fare better when the winds are from the north. Even so, countrywide annual averages are between 75 and 90.

The dehumidifier works away a few hours a day the year round, in my house.

Anecdotally, I have no verdigris problems due to the humidity. Things go mouldy but verdigris on keys (pipes, flute etc) only appear to get triggered by perspiration or around dirt build up in the key slots. No problems with a C flute made in Oz in 1986.

11

Could it have been somewhere salty, with retained salt keeping it moist? Things with metal parts that are not rinsed off with fresh water after a dunking in the sea often corrode quickly.

12

I was going to say something along the lines of what david_h said above. In addition to moisture and air, verdigris will grow faster at lower pH. So if the flute was close to the ocean, the little bit of salt in the air might make it susceptible. When I lived on the coast, I had to change the strings on my dulcimers twice as often as when I was inland due to the salt air.

Oddly, Wikipedia says that it’s an acetate, and that acetic acid is one of the chemical precursors. But any homebrewer who’s been at it for awhile knows that a way to get the oxide off the (copper) wort chiller is to soak it in vinegar. The acetic acid draws the oxide off, leaving a bright shiny copper surface behind. Of course, you do need to rinse it in clean water.

13

No-one has mentioned grease/oil. Obviously the copper content and stability of an alloy are significant factors, but I regularly see/deal with antique flutes heavily caked with verdigris in the kinds of locations Terry mentions, whilst other ostensibly closely similar instruments don’t have the same problem. The worst ones are usually also obvious victims of long-term excessive and inappropriate oiling.

I’m no chemist, but have long suspected that oil or moisture or both set up electrolytic conditions which leach the copper salts from the alloy into the gunk of in effect hydrogenated fat which builds up on instruments thus mistreated, and continues to do so when they are set aside long-term without being cleaned first. We also see this on stopper corks (greased, in a brass tube, with moisture penetration in the mix) and on tenon lappings in metal-lined sockets. Seized tuning-slides similarly - though there the metal salts element in the grease/moisture cement is often grey, derived from the tinning of the tube surfaces which was common in C19th flute-making. Instruments which haven’t been oiled much (bore oils, key oils for pillar mounts…) and were stored in dry conditions don’t tend to have the verdigris issues.

This was a typical example: https://www.facebook.com/media/set/?set=a.10150287430624271

14

It almost sounds like the oxidized copper salts formed in the areas someone would apply oil or cleaning products, eg the slide and key hinges etc but not in the lining. I wonder if someone may have made a bad choice of what product to use. Anything acidic or with salts in it. The concern you mentioned about lipid based oils could be an issue with brass, given enough time and a tiny bit of acidity (or moisture plus CO2 from the air) you could make fatty acids from the fats which would definitely enhance the oxidation process.