Verdigris (Was Re: further clarification on query)

[Jim Coleman, Sr.]

Hi Tim:

It has been my experience that I have seen verdigris only on one brand of
pianos. This manufacturer for many years treated its bushings with a
paraffin solution. It was a nice lubricant until it began eating away
at the plating of the center pins and when it got to the brass it turned
green (the verdi part of the word)

Jim Coleman, Sr.

PS If I'm wrong about the only brand, please correct me. I've been corrected
before and have survived. JWC


On Wed, 11 Feb 1998, Tim Keenan & Rebecca Counts wrote:

> List--
> 
> I should go and look at the archives, but my resources describe verdigris 
> as principally copper sulfate, with minor components of other salts. The 
> reaction happens everywhere copper is exposed to air containing sulfur 
> dioxide (SO2)[everywhere on Earth, to a greater or lesser degree, but 
> more near coal-burning power plants and active volcanoes] , but will 
> proceed faster in humid air where SO2 becomes H2SO3 (sulfurous acid) in 
> aerosol form.  It also forms as a result of contact with 
> sulfur-containing acids on skin.  It cannot form if the copper doesn't 
> come in contact with an acidic sulfur compound.
> 
> It occurs to me that prophylactic use of Protek or a similar product 
> which leaves a PTFE film a couple of molecules thick on the copper 
> plating of the pins ought to go a long way to preventing the accumulation 
> of verdigris in the first place. If pins were "Protekted" when new, and 
> occasionally thereafter, perhaps the problem could be greatly reduced.
> 
> I also notice that it doesn't seem to be directly related to age--perhaps 
> some bushing cloths use sulfuric acid as a mordant in the dyeing process 
> and it isn't always entirely washed out? I've seen pianos of virtually 
> identical ages but different makes (circa 1905) in a church in Hamilton, 
> Ontario (major steel manufacturing centre with coke ovens and stuff--lots 
> of SO2) where one piano had no problem and the other was quite gunked up.
> 
> Whaddya think?
> 
> Tim Keenan
> Noteworthy Piano Service
> Terrace, B.C.
>