Hi All,  The question of whether or not to use tan pneumatic leather
for the Duo-Art accordion pneumatics has always fascinated me because
Aeolian used leather (see note).  Also, Aeolian had really good bellows
cloth.  So, they could have easily used cloth instead of leather and
saved some money.  However, saving a few pennies wasn't their goal.

So why did they use leather?  Frankly, I don't know the answer, but
I have made some speculations.  It seems high plausible that Aeolian
did quite a bit of experimenting before making the final decision to
use leather.  Personally, I think they found that cloth was too good.

What I mean to say is that a perfectly air-tight stepper mechanism
that reacted very fast would have a tendency to make the music sound
mechanical.  By using leather, which wasn't 100% air-tight and was also
more dense than cloth, a certain amount of (for lack of a better term)
"mushyness" was introduced into the equation.  In other words, the
dynamic changes happened a tiny bit slower and/or they weren't quite
as snappy.  This gave the music a more human feel.

I correlate the use of leather for the accordions to the introduction
of the flexible flange finger in that the manufacturers were trying
to find ways to reduce the rigidity of mechanical music.  By creating
devices that weren't 'perfect', the mechanical nature of the music
faded.  We see the same thing in MIDI music.  When it's 'perfect', it
simply doesn't sound as good because the human ear is so sensitive
that it can tell when something doesn't sound humanly possible.  So,
by introducing a slight amount of error, we achieve a more desirable
result.

Note: Every single original Duo-Art mechanism I have ever worked
on had tan pneumatic leather.

Musically opinionated,
John A Tuttle
Player-Care.com
Brick, New Jersey, USA