I have no idea who or what the Hydrophane Company is.  However,
a couple decades ago, "Paintint" leather with a silicone treatment
was supposed to extend the life of organ leather.  It did just the
opposite.

Ten years ago I restored an original 2/5 Wurlitzer church organ.  The
organ was in perfect shape except that the previous service people had
"painted" the leather with liquid silicone treatment, and it destroyed
the leather.  You could even see the brush strokes on the leather were
the goop was applied.

Leather manufacturers sold all sorts of brush-on silicon treatments
for clothing, shoes, bags, etc.  Perhaps the stuff does work well on
clothing items.  However, organ leather is typically very thin and
I suspect this is the reason it is prone to advanced rotting.

I have also seen pneumatics treated with rubber cement to reduce
leather porosity.  The rubber cement has the same effect on the leather
as the silicon, in time.  The deterioration is _not_ immediate in
either material; it will look and last okay for some time and then
suddenly let go.

The Los Angeles based Murray M. Harris Company built superb church
organs circa 1898-1913 or so.  I have come across MMH organs that are
still playing on their original leather.  I learned from old timers
in the industry that MMH "painted" their pneumatics with egg white to
reduce leather porosity.  I have never used it and probably never will,
but it is an interesting treatment.  With the egg white material, there
is nothing petroleum-based to deteriorate the leather.

Tom DeLay
Salinas, Calif.