Back in the 1980s the Organ Historical Society (OHS) did testing on
leather because they noticed that pipe organ leather was turning to
powder in 5 or 6 years.  After over 100 years of using vegetable
tanned leathers on huge pipe chest pouches, gaskets and the valves
under each pipe things were getting pretty bad for organ builders
having to replace leather after less than 10 years when it used to
last 50 years.

In the intervening years, the DDT and other pesticides, herbicides,
fungicides that began to be used on the grass and feed that farm
animals eat became standard for most farm animals.  The skins now hold
residual chemicals from those as well as hormones and antibiotics.
This chemical slurry has drastically shortened the life span of organ
and pneumatic leathers.

The OHS testing involved a variety of leathers, from 150-year-old
organ pouches to the most recent fresh leather.  One of the things
they tested was the use of mink oil and neatsfoot oil on leather.
The stress tests showed that neatsfoot oil treatments showed zero
improvements as far as leather strength and airtightness.  The same
results were obtained for mink oil.

Furthermore the tanning methods tested found that alum tanned leather,
which is white with a yellow tinge to it and had been used on organ
reservoirs for over 100 years, only lasts 4 to 6 years before cracking
and deteriorating.  Vegetable tanned leather which is usually tan in
color lasted from 6 to 12 years.

The champ that testing turned up was chrome tanning, which leaves 2%
to 3% chromium salts in the leather and tested to a 50-year life span.
This is often leather that is gray white with a bluish cast to it.
One drawback using this leather is the tanning process opens pores
and makes the leather far more leaky for valve work.

They also found that there was a lost tanning recipe used by Robert
Morton and Aeolian organs which produced a dark maroon colored leather
that was found to be far stronger after 150 years than any of the other
leathers tested.  This leather tanning method has recently been found
according to some suppliers to the industry, but I find it difficult to
find as they are often sold out of this pouch leather.

If I don't know how the leather is tanned I can test it to find out
and I rule out using vegetable tanned or alum tanned under all
circumstances.

For sealing pouches at my shop, we use "Carter's Rubber Cement" exactly
like Ampico and Duo-Art did at their factories.  It should be thinned
down with solvent and applied with a finger while suction is applied
under the pouch.  Once it is dry dust it with Johnson's baby powder.

Carter's is no longer available at office supplies.  They look at me
like I have two heads when I ask for rubber cement.  However, rubber
cement such as used to be used for paper is now available at leather
craft stores where it is called "leather cement".  They also sell the
leather cement solvent as well.

If you go to a leather shop or warehouse, almost all the leather there
will be chrome tanned but I find that most of it is not usable for
organs or player piano systems.  I go to a national leather warehouse
to purchase leather but I take my testing equipment with me to test
each skin before I buy it.

Doug L. Bullock
http://thepianoworld.com/