Aging of hammer felt, leather, rubber, cotton

[D.L.Bullock]

Hammers are made of felt.  Felt is sheep fur and an organic material.
Organic materials oxidize.  Wool oxidizes.  If you had a 100 year old wool
sweater, you would not be able to wear it.  It would simply be too busy
turning into powder to be able to stay a sweater.  Piano hammers at an age
when they have turned yellow.  (the color that tells you the felt has
oxidized) cannot be strong any longer.  It takes quite a bit of strength in
the felt fibers to bounce off the strings as new hammers do.  That bounce is
what produces the tone that we like.

As the felt oxidizes and turns to powder, the grooves develop extremely
fast.  Haven't you ever noticed the yellow powder resting on the damper
blocks under a set of grooved hammers.  That does not happen under a 10 year
old set of grooved hammers like it does under a 90 year old set of grooved
hammers.

Anything that speeds oxidation deteriorates hammers.  Smoky environ is acid
and oxidizes felt.  Humidity can oxidize but too much makes the glue let
loose and the hammers come apart.  Chemical air pollution speeds
oxidization.  High oxygen levels, too.  Have you noticed how pianos in
Denver and other areas with thinner oxygen seem to last longer?  The same
things cause oxidation in other organic materials.  Players, my specialty,
are particularly susceptible to oxidation in the leathers, cotton cloth,
natural gum rubber, and other supplies used in player and pipe organ
systems.  This is also why the leather on hammer butts turns into powder and
wears through to the felt underneath in many older pianos.  Expecting that
deterioration is why I replace hammer butts on so many pianos.

D.L. Bullock  St. Louis
www.thepianoworld.com <http://www.thepianoworld.com>





-----Original Message-----
From: gordon stelter [mailto:lclgcnp@yahoo.com]
Sent: Friday, February 06, 2004 7:18 PM
To: Pianotech
Subject: Re: Aging of hammer felt


I believe that decades of humidity cycling usually
shrinks the felt, making the hammers harder.
     But I have encountered some truly wonderul
hammers ( a few ) over 70 years old. So this must
depend, to some degree, on the original mode of
manufacture and materials used.
     Thump