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Hi all,
The last few months bottom C & D on my Yamaha C5 started sticking. If the keys were depressed they stayed down. I'd had enough today with those strings resonating to every other thing I was playing so I took out the keyboard to have a look.

The counterweights between the two keys had a white powdery corrosion which had swelled out the weights and contacted the adjacent key which had a similar corrosion. I got a die grinder and carefully removed the corrosion but was surprised how deep it penetrated into the counterweight. I checked the other keys and found a couple more affected keys that were playing fine but the swelling had started. I took some pictures to show the issue.

[img]http://www.smartdecorprops.com.au/blog/2021/10/[/img]

Can anyone let me know what this is, how it happened and any ling term fix?

PS - Is it possible to upload photos to the forum instead of putting them on a separate URL??


"It is the mark of an instructed mind to rest satisfied with the degree of precision which the nature of the subject admits and not to seek exactness when only an approximation of the truth is possible" (Aristotle 384 BCE - March 7, 322 BCE)
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This is oxidation of the key leads. I'm not sure which metal is used nowadays; but I think it is still lead or some lead alloy.

I've read that the keyboards from some manufacturers exhibit this problem more often and more strongly, because apparently the wood contains certain acids that promote the corrosion.

When I remove such corrosion, I try to cut it (e.g. with a sharp chisel) rather than grind it, to avoid dust. I always take care not to breathe or spread the dust, and wash my hands afterwards, in case it is indeed lead.

In terms of a long term fix, others may have better suggestions, but my first approach would be to seal the surface, i.e. paint or varnish the weight, in order to keep oxygen out.


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Oxidizing lead expands, so in worst case:
[Linked Image]

I'm not saying that it will definitely happen in your case, but you should be aware of this. It usually happens in very old neglected pianos so you most likely have time and shaving them to be flush with the key might be ok fix for now.

Last edited by ambrozy; 10/13/21 09:36 AM.
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I'm definitely with the use a chisel post. Grinding to dust can't be good and a chisel works well. When I have done this I've always varnished over the resulting face but I really don't know if it is an effective cure.


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None of this will solve your problem, but the problem is interesting. Lead is noble and normally shows very little corrosion in the atmosphere, which you can prove for yourself by looking at lead roofing flashing when you drive down the street. I've seen 40 year old lead flashing that had no corrosion, just a discoloring. Lead is sort of like some of the structural steels like cor-ten that form a protective layer that prevents further corrosion. It will react if exposed to chlorine, so it's possible it reacts with the salt from your sweat to form lead chloride, which kind of looks like your pictures. I guess it might suggest those weights should be handled with rubber gloves to avoid getting skin salts and oils on them during assembly or repair.

The weight may be alloyed with something that's cheap, like zinc, or it might be some other high Z metal (hopefully not depleted uranium). Given all the contemporary problems with lead, I would think manufacturers would stampede to find a replacement. Zinc can develop what's called white rust, that might be what you're seeing. It forms if there isn't enough air flow over the surface to form a protective layer on the zinc.

Your corrosion really looks gnarly, if you're near a university it might be interesting to take it to a chemist or materials lab to find out what's really going on. I would whole heartedly agree with the suggestions to not grind it until you find out what it is. As a welder I can tell you there are metals and corrosions that will ruin your day if you inhale the dust or vapor.


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It is indeed unclear why lead sometimes corrodes because it really shouldn't and I don't buy the "acid in wood" story either, it doesn't even touch wood where it corrodes.

How old is your piano?

Last edited by ambrozy; 10/13/21 02:30 PM.
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Just to say I've seen this corrosion in many pianos. Sometimes in the damper flanges behind the action in grands... particularly Bechsteins from 1900 ish. Most definitely not caused by human contact. I've always assumed a damp atmosphere was to blame...but it is an assumption, I have no scientific knowledge about it.

Last edited by N W; 10/13/21 05:06 PM.

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Search NAVSEA, Curator of Navy Ship Models.
This is the only true research that I've seen.


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Originally Posted by MarkL
Lead is noble and normally shows very little corrosion in the atmosphere, which you can prove for yourself by looking at lead roofing flashing when you drive down the street. I've seen 40 year old lead flashing that had no corrosion, just a discoloring. Lead is sort of like some of the structural steels like cor-ten that form a protective layer that prevents further corrosion.

Lead is no noble metal. Several acids, amongst them volatile organics, can attack it. This is also the reason I wouldn't discount the theory about the acidic wood completely.

But you're right in that it generally passivates by forming a native layer of oxide, a patina.

Originally Posted by MarkL
The weight may be alloyed with something that's cheap, like zinc, or it might be some other high Z metal (hopefully not depleted uranium). Given all the contemporary problems with lead, I would think manufacturers would stampede to find a replacement. Zinc can develop what's called white rust, that might be what you're seeing. It forms if there isn't enough air flow over the surface to form a protective layer on the zinc.

Thank you, this sounds like a very plausible hypothesis to me.

Originally Posted by ambrozy
It is indeed unclear why lead sometimes corrodes because it really shouldn't and I don't buy the "acid in wood" story either, it doesn't even touch wood where it corrodes.

The proximity to a source of volatile corrosives, e.g. organics, would be enough. On the other hand, if there really are corrosive volatiles around, there should be plenty of verdigris on the bass strings and brass parts...


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Hi Ambrozy,
The C5 is a 1986 model so 35 years. I'm wondering if someone may have used detergent to clean the keys sometime in the past and some liquid dripped down on some keys. The majority of keys are fine


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Maybe had mice in there sometime? Urine might not be good...but would leave a stain I should think.


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Originally Posted by Mark R.
Lead is no noble metal. Several acids, amongst them volatile organics, can attack it. This is also the reason I wouldn't discount the theory about the acidic wood completely.
I didn't mean it's a noble metal in the physics/electron d-ring sense, I mean it's noble in the atmospheric corrosion sense.


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Thanks for that David-G.
Yes, an interesting thread and obviously not an uncommon problem.

I've worked out how to put the photos into the post :-)

These are the keys that were sticking:
[Linked Image]

These are a couple of other keys around middle C that, while not sticking, still had swelled out a bit:
[Linked Image]

The more I think about it the more I am coming to the conclusion that some sort of liquid seeped down a few keys years ago, possibly detergent cleaning the keys, which led (pun intended) to the problem.


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Player pianos used to be tubed with lead tubing, which would get oxidized, and it is not likely that moisture got into those tubes except through the air, so oxidization can happen without anything more than exposure to the air.


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Can this be chemical oxidation, similar to the bronze disease?
Some salt/chlorines from a humid (usually RH 60+) air or from whatever you used to clean keys could settle on counterweights with time. Very hard to cure, easier to replace them.

Last edited by VladK; 10/16/21 08:47 PM.

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