S&S green goop

[Ron Nossaman]

At 12:37 AM 6/20/99 EDT, you wrote:
>
>In a message dated 6/19/1999 5:15:28 AM, you wrote:
>
><<List,
>Christopher has asked what causes the verdigris found mainly on Steinway
>centers.  We've all probably heard so many reasons for this green goop
>that we aren't sure which is correct.  Several years ago, I was in a
>class given by Fred Drasche.  I remember him saying that "in the old
>days, we (at Steinway NY) used to dip each center pin in lamb's fat
>(tallow) before inserting them."  He went on to explain that although
>the tallow allowed the center to work very well for many years, he
>believed that eventually, this practice was the cause of the majority of
>the verdigris.
>Jim Krentzel
>
>>>
>
>Ah, very interesting, now we're getting somewhere.  But it begs the question 
>- what is it that turns the tallow green???
>
>Christopher
>
>


Hi Gang,
Like I suggested last time around... perhaps NaCl; a little residual salt in
the tallow to increase conductivity and boost the corrosion process. Dale's
fatty acid explanation makes sense too. Brass is, after all, a copper/zinc
alloy. Immersed in the right electrolyte, you'll get corrosion. Pull the old
stem out of the hot water shutoff valve to the washing machine and see how
much of it is left (I suggest turning the supply off first). In an
electrochemical series table, copper is listed at a low positive potential,
and zinc as a mid-range negative. That is, if I'm reading this right.
Remember that zinc is the casing and negative terminal in the old style
carbon/zinc flashlight batteries. Zinc should corrode more readily than
copper, but the copper corrodes to some degree too, supplying the green.

Of course, this could have all been avoided by a light application of
tincture of wolf, early on, to eliminate the sheep tallow altogether.

 Ron