[ Bernt Damm wrote in 110909 MMDigest:

> I am now favoring the theory that it has something to do with the
> temperament of the slow detuning that occurs in some particular
> pianos under certain conditions ...

There are two other factors which have occurred to me while thinking
about this matter further.   First, 19th-century music wire was of an
inferior quality compared to modern steel wire, and likely had a
different tone quality as well.  Combining internal qualities of the
wire with crystallization due to aging under tension may inform the
overall tone quality.

Secondly, music wire sounds best when it is under ideal tension, near
to the breaking point of the material. A piano that has not been tuned
for decades will most likely drop in pitch, and the lower tension also
likely informs the overall tone quality.  As I stated before, in my
experience 19th-century pianos can be found a minor third flat, and not
usually more; perhaps an instrument would have to be de-tuned more than
one-half step to have the lower tension impact the generated tone
quality.

Mark Ritzenhein