A research scientist named Harley Piltingsrud did an extensive study on
the aging of organ leather.  His paper is available in a 1987 booklet
called "Aging of Organ Leather" published by the Organ Historical
Society.   He will be speaking again at the American Institute of Organ
Builders convention in Los Angeles in October, 2002.

In a nutshell, he found that chrome tanned leathers with 4% or greater
chrome salt concentrations, [remaining] when the leather was reduced to
ash, could be expected to last 40 to 60 years.

John M. Nolte - Nolte Organ Building
Milwaukee, WI 53215

 [ A short biography about physicist Harley Piltingsrud is at
 [ http://www.pipeorgan.org/convention/2002/piltingsrud.html
 [ His 48-page booklet, "The Aging of Organ Leather", is described
 [ at http://www.ohscatalog.org/piltanagofor.html  -- Robbie