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<div style="color: black; font-family: arial,helvetica; font-size: 10pt;"><blockquote style="padding-left: 3px; border-left-color: blue; border-left-width: 2px; border-left-style: solid;"><pre><tt>So it would appear that it's the kind of wood used
in keys, rather than anything else, that is the culprit with this problem. Also,
if the air is moving more around the piano it's probably a good thing. So
perhaps having a closed fallboard will contribute to a concentration of the
acids in the micro-environment around the keys?
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<div>Again, if it is the wood, why are some leads corroding, and some are not, in the same piano? Or is there that much difference in the fibers of a set of keys that makes some leads corrode, and not others? Or, since keys are made from three or four boards end glued together, with one or more boards coming from different trees, is there that much difference in the acid content from one pine tree to another? </div>
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<div>So it seems that in order for the corroding problem not to surface again, perhaps the only real solution is a new set of keys, made from basswood, weighted with a set of electroplated leads. Yeah, right. Try to sell that job to a customer with a 50 year old Kimball spinet. </div>
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<div>Wim</div>
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<div style="color: black; font-family: arial,helvetica; font-size: 10pt;">-----Original Message-----<br>
From: Allen Wright <akwright@btopenworld.com><br>
To: pianotech <pianotech@ptg.org><br>
Sent: Tue, Mar 12, 2013 1:41 pm<br>
Subject: Re: [pianotech] Expanding leads<br>
<br>
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On Mar 12, 2013, at 10:47 PM, <a href="mailto:pianotech-request@ptg.org">pianotech-request@ptg.org</a> wrote:
David,
Like Wim, I always assumed that this was caused somehow by humidity, and was
simply "oxidation". So that perhaps pianos kept in damper environments might
suffer the worst. But it seemed to show up in the most expensive fine older
instruments as well as low quality ones.
It's not the quality of the piano (nor humidity) that has any effect on this
phenomenon; rather, it's acetic acid (and formic acid to a far lesser extent) in
the wooden keys themselves that is the cause.
I only just learned about this last week when I noticed (by sheer coincidence in
the archives) a mention by Laury Libin about this subject, either on this list
or perhaps CAUT some months ago. He references an article from a US Navy
website, on the challenge of dealing with deteriorating lead parts in ship
models. A couple of the most relevant quotes:
The chemical process is this: "acetic and some other acids, in the presence of
carbon dioxide, catalyze with lead to produce lead acetate and lead hydroxide.
Lead acetate and lead hydroxide together react with carbon dioxide and form lead
carbonate. Lead carbonate then releases acetic acid and the process becomes
self-sustaining. ...the formed lead carbonate is not just a substance clinging
to the surface of a casting, it is the surface of the casting transformed to
powder (... ) a portion of the lead is gone and lead carbonate is left in its
place. The lead carbonate releases acetic acid which can continue the process
until the lead part is progressively consumed from the outside, inward."
"A simple way to prevent woods from off-gassing acetic acid would seem to be to
seal the wood using an acid-impervious coating. But most kinds of wood sealers,
paints, and clear finishes are not impervious to the passage of acetic acid from
woods, and indeed, the coatings might further contribute to the
micro-environmental problem. To date, researchers have found no product which
can be applied as a liquid and which fully seals wood to suppress the emission
of acids. Two part epoxy and some urethane paints appear to offer a limited
degree of barrier. Shellac, while not an acid producer, does not offer any
protection."
Three categories of Very Harmful, Moderately Harmful, and Less Harmful woods are
given. Basswood is in the very harmful column, whereas Sitka spruce and Pine are
in the less harmful column. So it would appear that it's the kind of wood used
in keys, rather than anything else, that is the culprit with this problem. Also,
if the air is moving more around the piano it's probably a good thing. So
perhaps having a closed fallboard will contribute to a concentration of the
acids in the micro-environment around the keys?
To extrapolate from all this a bit further, it would seem that lead is perhaps a
fundamentally problematic and ultimately unsatisfactory material to be used in
weighing keys, at least in the long term. I'm not sure what else could be used,
although the article does say that electroplating the lead may be an effective
preventive measure. That might be prohibitively expensive.
I'm glad to finally know that this is not an "oxidation" problem, and to have
some of the mystery explained. For anyone interested in reading the whole
article, here it is (and once again, all thanks to Laurence Libin for posting
this originally).
<a href="http://www.navsea.navy.mil/nswc/carderock/pub/cnsm/lead/lead_01.aspx" target="_blank">http://www.navsea.navy.mil/nswc/carderock/pub/cnsm/lead/lead_01.aspx</a>
Best regards,
Allen Wright, RPT
London, UK
p.s. I hope I've posted this correctly in terms of format. I get the daily
digest of the list.
>
> Message: 4
> Date: Tue, 12 Mar 2013 13:27:30 -0700
> From: "David Love" <<a href="mailto:davidlovepianos@comcast.net">davidlovepianos@comcast.net</a>>
> To: <<a href="mailto:pianotech@googlegroups.com">pianotech@googlegroups.com</a>>
> Cc: <a href="mailto:pianotech@ptg.org">pianotech@ptg.org</a>
> Subject: [pianotech] Expanding leads
> Message-ID: <00bf01ce1f60$054f07f0$0fed17d0$@net>
> Content-Type: text/plain;        charset="UTF-8"
>
> While I have run into expanding lead problems periodically generally they seem
to have been reserved for "lesser" pianos. Today I found a 1950's Boesendorfer
200 with leads expanding both in the back action and the keys to the extent that
they were binding on their neighbors and on the verge of splitting things. Of
course I will have to remove and replace, a large task considering the new
weigh-off at the key end that will be required.
>
> My question is what is it that causes that reaction and why after such a time
does it happen. This is some 60 years later.
>
>
> David Love
> <a href="http://www.davidlovepianos.com" target="_blank">www.davidlovepianos.com</a>
>
>
>
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