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Removing Green Spots (Verdigris)

Although brass doesn't rust, there are still a few ways in which it can corrode. For the most part it's relatively harmless except in extreme and rare circumstances - but it can leave your horn looking rather shabby.

If you took a piece of plain brass, gave it a shine, and then hung it up on an indoor wall for a few years it would eventually (and quite slowly) tarnish. Its bright, yellow sheen would fade and it would take on more of a matt appearance as the colour slowly faded to a sort of straw brown. This is perfectly natural process called oxidation, and for the most part it's merely considered an inconvenience if you're partial to keeping your bits of brass nice and shiny.
Heavy verdigris on bare brass hornBut when you change the environment to include contamination of the brass by moisture, weak acids, pollution and various organic compounds - it can all get rather messy in a very short space of time. Assorted spots and blemishes of various hues may appear - along with the distinctive green spots that are known as verdigris (pronounced ver-dee-gree).

Chemically-speaking, verdigris is copper carbonate (typically with a few other chemicals thrown in for good measure) and its appearance is a cause for concern because it looks rather unsightly and can be difficult to shift...and if left to its own devices for long enough it can damage the brass. Granted, it'll take a very long time indeed for it to do any significant damage, but it can certainly leave a pock mark behind if it's not dealt with in relatively short order. So it clearly pays to get rid of the stuff as soon as you spot it. However, this isn't always an easy task because it's quite tenacious - and will shrug off the usual methods of cleaning. You'll need to get a lot tougher to get rid of it and, as we'll see shortly, this can have implications when it comes to preserving the finish of a horn.

It probably goes without saying that prevention is better than cure - and without getting too bogged down in technicalities it's sufficient to say that if you put away a bare brass horn (or one with some missing lacquer/plating) when its wet, you're effectively sowing the seeds of verdigris. Having a horn made from nickel silver is no defence either - it's still liable to attack, though to a lesser degree. Hence the need to ensure the horn is dry before shutting the lid on the case.
Unfortunately this isn't always practical; the last thing you want to be bothered with at the end of a gig is having to mop out the bore of the horn...and then wipe down the exterior. A workable compromise is required, and it's usually sufficient to whip the horn out of the case when you get home and leave it to stand for an hour or two somewhere moderately warm and dry. It probably won't completely prevent the formation of those nasty green spots, but it'll go a long way to slowing them down.

Ultimately, then, most sax players are going to have to deal with verdigris at some point (or pay to have someone else do it) - and the aim of this article is to show you what methods are most effective...and to highlight the pros and cons of each.

Verdigris-spotted bellThere are two ways in which verdigris can be removed; the first is by mechanical action - which includes scraping, brushing, abrading and polishing. The second is by chemical means, which, as the terms suggests, involves popping something on the spots which will remove them without the need for a lot of elbow grease.
We'll tackle the mechanical methods first.

Here's our unfortunate testbed victim for the first part of this project - an old Super Dearman alto that's seen better day and now serves as a spare parts donor horn.
It's not that badly affected by verdigris, but you can see a few green spots here and there on the bell - which for most players should be pretty typical of the level of 'infestation' they're likely to encounter.
Infestation isn't really the right word (though what you'll see later in the article probably qualifies as such) and a more accurate and useful description would be 'encrustation'. Verdigris forms in layers; it begins with a base layer which grows outwards and a surface layer which grows upwards. The surface layer tends to be quite gritty and crumbly - which means you can remove a fair amount of it with nothing more than a fingernail.
I've numbered the areas that are going to be treated so that you can refer back to this shot as a point of reference.

Scraping the verdigris with a fingernailHere's a little before-and-after shot that shows just how much of the verdigris can be removed by giving the spot (No.1) a couple of scrapes with a fingernail. As you can see, it hasn't removed all of it - but the spot is a lot less distinct. If your nails could stand it you could probably go a bit further (and you probably will, because it's one of those things that are curiously satisfying).

If you have no nails, or at least none that could/should be used as tools, you can use a wooden stick or a plastic scraper (with a bit more care). Don't be tempted to used anything harder as there'll be a risk that it would dig into the brass.

You might well decide that this level of cleaning is good enough - and if you spent some time picking over all the spots you'd make a reasonable improvement to the way the horn looked. But verdigris tends to grow (given the right conditions), so it might not be long before you'd be back where you started and have to do it all over again.
A better bet would be to carry on and remove as much of the green as possible - and for this we're going to need a little help.
The first thing to do is to clean the affected area. We already know there's a relationship between brass, moisture and verdigris - which means that washing the area with water isn't a great idea. A far better bet is to clean the area with a solvent - and you won't do much better than cigarette lighter fluid (AKA naphtha).
There are no special considerations to this part of the process - simply sloosh some fluid onto a dry cloth and wipe it over the area you wish to treat (keeping in mind that it's flammable take due precautions).
While naphtha isn't generally known for it ability to remove verdigris you might well find that some of the smaller spots may disappear - and those that remain will take on a paler, more powdery look after the solvent has evaporated.

Using the fibreglass pencilWhen it comes to mechanically dealing with the base layer there are three options; scraping, brushing and abrading. Scraping tends to be very hard work, and is the method most likely to result in damage to the brass - so we're not even going to go there, even though it can be a very precise method of dealing with individual spots. Brushing is a lot easier, but you'll need something rather more effective than a paint brush or an old toothbrush - and the fibreglass pencil fits the bill perfectly.
You can pick these up quite cheaply from all the usual places online, or in artist/hobby shops. They're built like a retractable pencil except that rather than having a length of graphite that extends from the tip every time you twist the tail of the pencil, a bunch of tightly-packed fibreglass strands appear. The fibres are quite hard, which gives them a scouring action and makes them ideal for the job. However, they're also quite brittle...and this means that they'll shed tiny pieces in use - and if you've ever handled any fibreglass before you'll know that it can make you itch like crazy. It's one of the drawbacks of this method - so take care to avoid getting any on your hands, clothes, furniture, carpets etc. The safest bet is to do the job outside, but failing that do it over a few sheets of newspaper...and try to avoid breathing any of the dust in.

Another drawback is that the pencil isn't quite as accurate as a scraper. As you can see from the before-and-after shot it's quite hard to confine the action of the pencil to the spot you're working on - so you're always going to end up with a larger working area than you might have intended. It'll certainly help if you keep the brush quite short; anything much longer than shown in the photos tends to result in the fibres splaying out. You can see, too, that it's completely removed the green spot - but in so doing it's cut through the surrounding patina to the clean brass beneath it. It might look a bit draconian but in fact very little brass has been removed...though note that pile of potential itching powder surrounding the job (wipe it off with a tissue dampened with lighter fluid, then dispose of it immediately).

At this stage you're technically done; the verdigris has been removed and is unlikely to return unless this area is left wet for any length of time. Now, I don't mind the matt finish the pencil has left behind - but you may feel you'd rather bring the bare brass back to a which case a quick rub over with a suitable metal polish will do the job - though it's likely to widen the work area even more so as it'll also remove the surrounding patina/tarnish.

Which raises the point that one of the issues you'll probably have the deal with is that of any surrounding finish. In that last example the green spot was on a reasonably large patch of bare brass - but what if it's surrounded by lacquer or plating? To be frank it's really an exercise in damage limitation. A spot of verdigris will have long since eaten right through any cosmetic finish, and the object of the job will be to remove it as neatly as possible while leaving the surrounding area intact.
Fibreglass pencil on lacquerIf you're careful and patient the fibreglass pencil can do a reasonable job. I treated an area (No.2) dead centre of this patch of lacquer (there was no verdigris spot on it) and you can see that there's just a small spot dead centre where the pencil has cut through the lacquer to the brass below. However, the surrounding area has held up pretty well. You can't really see it in this shot but the lacquer hasn't come off entirely unscathed...there are lots of very fine scratches on it now. As before you could choose to leave it as it is - or you could finish up with a drop of metal polish. It may well widen the work area a little, but it would also smooth off the scratches in the lacquer. The same would be true of a plated surface - but it would very much be a 'see how you go' job, and stopping before you removed too much of the finish. That said, it wouldn't hurt to remove a little of the finish around the affected area as there could well be particles of verdigris trapped beneath the surrounding edges.
Much of the above also applies to factory patina finishes. Although such horns are technically bare brass, the chemical tarnish represents a surface finish - and you may want to preserve as much of it as you can. That said, any treated areas will soon tarnish of their own accord and should more or less blend into the factory finish over a period of time.

Fibreglass pencil on untreated areaAnd in terms of the 'see how you go' approach, it may not be necessary to take the spot right back down to clean brass.
I'm working on spot No.3 here, and I've brushed it enough to remove all traces of green but haven't yet cut through the tarnish that was lying beneath the spot. In fact I don't really need to - the green is gone, and going any further would only be a cosmetic job. But the wider surrounding area is all why bother carrying on? It's a judgement call that only you can make.

Using steel woolAnother option is to attack the spots with wire wool.
There are many different grades of wire wool, ranging from coarse to very fine - and for our purposes a very fine grade is what's required. Wire wool is typically graded using a series of zeros - with 0 gauge being the coarsest. What I'm using here is 0000 (quadruple zero) gauge.
It's really quite fine - so fine, in fact, that it can be used to bring a shine back to nickel plated keys (nickel being very tough stuff that doesn't scratch as readily as brass or nickel silver).
It's still plenty tough enough to deal with verdigris, however, though it suffers from being even less accurate that the fibreglass pencil. This is, or was, spot No.4 - and you can see that the wire wool has done just as good a job as the pencil did on spot No.3...but has removed the tarnish from a much wider area. You could probably improve on this with some due care and attention, but not by much. On the plus side, it leaves the bare brass a fair bit shinier than the the point where you might not feel it's necessary to finish up with a drop of polish.

Orange stick and AutosolThe next method (on that faint spot just to the left of No.4) uses a combination of metal polish and a stick (in this case an orange stick). You could use almost any metal polish (Brasso being a typical example) but I've gone for a paste (Autosol) because it's rather less messy and tends to adhere to the stick better.
This method is as accurate as the size of the tip of the stick, which you can shave to size to suit. It leaves the best surface finish of all but it's a lot slower than the more abrasive methods discussed earlier. It's also a lot fussier in that the polish tends to obscure the job in process - so the only way you can gauge your progress is to wipe the surface from time-to-time and then apply more polish.

There are a few variations on a theme. For example, you could replace the metal polish on the stick with a piece of fine grade carborundum paper (800 grit would be a reasonable choice). A piece glued to the tip of the stick would be far less messy in use than polish and it would cut through the spots much more quickly - and it'd be quite accurate...but I think you'd soon get fed up of having to replace the abrasive paper on a very regular basis.
You could, of course, just use the corner of a piece of folded carborundum paper...

Brass brushes are an option, but it's not easy to find one that's both small and fine enough. If it's too big and coarse it won't be at all accurate and will leave deep marks in the brass. Perhaps the best chance of finding something suitable would be to look in places where they sell accessories for micro drills (such as the Dremel). Incidentally, and assuming you have one, I wouldn't recommend using a micro drill with a brush fitted for this job...unless you really, really know what you're doing. And while I'm here, a steel brush is a big no-no.

Citric acid crystalsOn the face of it, the mechanical methods seem to work quite well - so why bother with chemicals?
Well, it's no big deal to tackle a few green spots that have appeared on the bell...but what if they're sitting beneath the action, or even on it. Getting your fingers into tight corners isn't going to be easy unless you're prepared to remove a few keys - and even then there's no guarantee you'll be able to clean the verdigris out of all the little nooks and crannies. In this case a chemical solution works quite well - the process removes the need for elbow grease and thus makes it a more practical proposition for dealing with verdigris in tight corners.

The big problem is that it's insoluble in water, alcohol and organic solvents - which means that treating it with any of these standard cleaners will, at best, remove any loose particles but won't do much about the remainder...which will be stuck to the brass.
However, it decomposes in diluted acids - which means that plain old malt vinegar (acetic acid) straight out of the bottle will remove it. This is all good and well, but dabbing loads of vinegar over your horn is likely to leave it smelling rather piquant for quite a while - which is why I recommend citric acid for this job. It's slightly stronger and doesn't have a noticeable odour. It's typically bought in crystalline form and is usually available from general hardware stores, as it's quite useful for cleaning jobs around the house. It's dead cheap too, at barely a couple of quid for a box.

There are a few caveats (ain't there always) to this method, and I'll expand upon them as we go through the various stages - but it's worth pointing out from the start that there's a safety issue to take note of. If you get any of this stuff in your eyes it'll be unbelievably painful - at least for a little while. It's unlikely to do any severe damage though - but you'd well well advised to wear safety goggles. You may also want to wear rubber/nitrile gloves. The acid won't eat your skin away but it's not exactly good for it either, and if you have any cuts or scratches on your hand it'll sting like a sod.
Incidentally, and just for info - verdigris converts into copper oxide when heated, so it's technically possibly to remove verdigris with the aid of a gas torch. However, copper oxide is black in colour - so it probably won't look all that attractive...and as yet I haven't tested the technique so can't say just how hot you'd need to get things.

Applying the acid solutionI mentioned an 'infestation' of verdigris at the top of this article, and the horn I'm going to be using to demonstrate the acid cleaning method is as good an example of it as you're ever likely to see.
It's a TJ RAW (as shown in the opening photo) - which is a bare brass horn that's finished with a chemical tarnish. It's a popular finish these days, but one that doesn't really suit players who are inclined to blow a little 'wet'...or a lot wet, in the case of this horn's owner. Unless such players are fastidious about drying the horn off properly after playing, the verdigris will home in on the bare brass like jazzers round an all-you-can-eat free buffet.

As with the mechanical methods, some pre-treatment will help to speed things up. If you only have a few spots to deal with you might want to give them a bit of a scrape first - otherwise you can skip this step and go straight to wiping over the target area with some cigarette lighter fluid. This too is probably unnecessary, but it certainly won't hurt to remove any oily residues before applying the acid.

The next step is to make up an acid solution, which is done by dropping a level teaspoon of the crystals into a small cup of warm water. There's no need to be too precise about it - a little more or less either way isn't going to make a significant difference. Give the solution a bit of a stir to ensure all the crystals dissolve.
A pipe cleaner bent double is perhaps the most effective means of applying the acid to the body. You could use a small brush but it tends to result in dribbles and it lacks the stiffness of a pipe cleaner - which comes in handy when you're working on stubborn spots.
Dip the pipe cleaner into the acid, drag it over the rim of the cup to squeeze out the excess then apply it to the spot you wish to work on. Rub the cleaner lightly over the area - it's a chemical action, so there's no need to scrub with any real force.
The treated areaIf you have a large area to treat it's best to break it down into smaller sections and treat them in turn simply because it makes it easier to keep an eye on the process and to watch out for dribbles. Mop them up with a dry tissue as soon as you spot them, and then rub over the area with damp tissue followed by another dry tissue. If you fail to spot and deal with a dribble it won't destroy your horn - but it may leave what looks like a water mark on any bare metal.
If you can be bothered - and you have the space on the horn to do so - you can mask off any areas that you want to protect from the acid with clingfilm. You'll still have to watch out for dribbles, but it won't be quite such an issue if you miss one or two.
Keep an eye out too for any dribbles that fall onto blued steel springs. It won't dissolve them, but it may result an a blob of minor surface rust if left to dry out of its own accord. If this happens, simply rub a bit of 0000 gauge wire wool over the spring and it'll clean the rust right off.

I'm treating quite a large area here, and one that's heavily contaminated with verdigris. What I want to do is keep working the area - keeping it moist and lightly rubbing off any verdigris particles that have been loosened by the action of the acid (note the green discoloration on the tip of the pipe cleaner).
Wiping the grime offI've marked out on the photo the area on which I'm concentrating for two reasons; it's about the largest area that's manageable - unless you're working on a stripped-down horn and you intend to treat the entire body - and it'll also serve as a comparison with the untreated areas at the end of the job.

The process is going to happen at different speeds depending on how much verdigris the acid has to work on. Lighter spots may well start to fade quite quickly, but heavier encrustations are going to need repeated applications - such as at the lower side of this tonehole.
If you feel the process is getting a little uneven, just wipe a tissue over the areas where you think you've done enough and confine further applications to the grimier spots. If it all gets a bit messy and you can't quite see what's going on, wipe over the area and apply fresh acid.

It's not going to be an instant process, but when you think you've done enough you'll need to wipe over the area with a clean, dry tissue. If you see any marks left by stray dribbles you can use the tissue to work what remains of the acid over the affected area to blend it in.

Rinsing the acid offYou'll now need to neutralise the acid - and this can be done with tissues soaked in water or by carefully spraying water over the treated area. If you really want to push the boat out you can always add a teaspoon of baking soda to the water to increase the alkalinity...though I've never found it necessary.

Drying after first treatmentYou now need to let it all dry off - and if you're in a hurry you can speed it up by running a hair dryer over the treated area.
Don't be too dismayed if you see light green patches appearing as the metal dries (below, right). It's unlikely you'll catch everything first time around, and the moisture makes it harder to see the areas you've missed or haven't treated enough.

It's very much a case of 'rinse and repeat - though at this stage you might want to focus on the smaller and more stubborn spots first, before attacking the larger and lighter ones.
Treat, mop, wash and dry until you're happy with the end result.

Here's the finished area (below left) - and while it's perhaps difficult to spot the transition on the lower part you can clearly see the boundary line at the top, just below the Bb tonehole.
You can see that the treated area's completely free of verdigris - but it's come at the cost of some change to the original factory-applied patina. The crystalline structure of the brass is more evident, as is its natural colour in some places - all of which leaves it with a more mottled look.

The cleaned hornHowever, it looks a hell of a lot better than it did - and it's still much more of a 'vintage' finish than that which would have been achieved by mechanically removing the verdigris.
There's also a bit of the original finish left behind, which tells you that the acid cleaning process is very much a surface event....rather than one that eats into the brass in any significant way.

A key tonehole - before and afterAnd for further comparison, here's a before and after shot of the area comprising the A tonehole and the compound bell key pillar - both of which were severely affected by verdigris.
The loss of the factory finish is rather more evident here - but as with the low B tonehole area it's still a lot less conspicuous than abrading the verdigris off and taking the metal back down to fresh brass.
If you have a sharp eye you might spot that the low C# spring (fitted to the lower side of the compound pillar) has gone slightly rusty at its base after the treatment. As mention earlier, a quick rub with some fine wire wool will sort that - and if you wanted to go the whole hog you could run a blue Sharpie pen over the spring to restore the colour. Get one with a wide nib. If you get any ink on the pillar it'll wipe of with a drop of cigarette lighter fluid on a cloth.

Now that the horn looks a lot cleaner you might be interested in keeping it that way - at least for as long as possible (this is kinda why lacquer was invented).
The most reliable solution is to use a wax finish on the body. Renaissance Wax is touted as a good option, but I've used good quality car waxes with good results. Anything that's designed to protect paintwork against the ravages of pollution, water and direct sunlight is going to shrug off the odd bit of gob. And you can use it on your car.

Addendum March 2020:

Untreated bellHaving posted a link to this article on Cafesaxophone - where I regularly post news of updates - one of the members (Ivan) asked me a very pertinent question that wasn't covered in the article: "Is it necessary to neutralise the acid you use to clean away verdigris? What would be the consequences if not done?"
It's an excellent question - and one that I admit I couldn't answer authoritatively simply because I'd never actually tested what happens in such circumstances. Sure, empirically I could say that very little, if anything, is likely to happen...but it's always preferable to have some hard data. So I set up a test.

Acid-treated bellI degreased a section of the bell on the poor old Super Dearman alto and marked off three sections - as shown on the left.
All sections were treated with the acid mix (as detailed above) twice over a 10 minute period. Following the treatment the section marked ++ was left as is, section + was wiped with a dry tissue and section - was wiped twice with a wet tissue and then once with a dry one.
The shot on the right shows the results.

No surprises here - the acid has done exactly what it's supposed to do and removed some of the tarnish from each section.
The horn was then left in the workshop for around five weeks, during which time it was subjected to various changes in temperature and humidity. It also got handled and (there's no polite way of saying this) gobbed on - though to be accurate I tried to reproduce the pattern of moisture droplets from the keywork by blowing raspberries at the bell (taking very great care to ensure that no-one was watching...).

Bell after five weeksAnd after all that time, were there any changes? See for yourself? As far as I can see there's absolutely no change other than that which occurred at the time of the acid application - and perhaps a slight dulling of the cleaned sections due to the natural tarnishing process.

I even gave the joint below the ++ section a lick a while back, just to see if I could taste any residual traces of acid...but all I got was that slightly potatoey taste of brass (not nice).
To be honest I was a little surprised. Section ++ was a very tough test - two coats of the acid solution and a good few nooks and crannies on the bell joint to soak up any excess - but as you can see, there's really nothing to see.

I'd still recommend cleaning the acid off - it's the sensible thing to do - but at least you know that any spots you miss are unlikely to cause any significant problems.

I think five weeks or so is time enough to see some results - but just to be absolutely sure I'll leave the horn exactly as it is and keep and eye on it over the coming months. If anything changes I'll be sure to let you know. Don't wait up.



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