Hi All, Kim Bunker here from www.playerpianos.com.  Most all piano
hammers are made of 100% felt that has been compressed to 10 pounds
weight, 12 lbs, 14 lbs, 15 lbs, 17 lbs and 19 lbs.  (Some manufacturers
use felt as much as 22 lbs and more!)  These weights are the total
weight of the felt prior to shaping it over the wood molding.

The wood molding used as the hammer core itself was beachwood, walnut,
maple and even pine.

The original factory voicing was accomplished with starch and steam
pressure.  Knowing this about what piano manufacturers did at the
factory is very important to any qualified voicer or technician today
because starch is broken down with ammonia.

Here is and experiment to try: take and old upright piano that has been
played to death and, in the high end on of those terribly bright
hammers that your going to replace, pick one or two hammers that sound
like breaking glass.  Okay, now get an eye dropper and fill it with
pure ammonia.  Put on no more than two drops per hammer, one drop right
on the striking part and the second if needed 1/4" away from the
striking part of the hammer.  Do not play the piano for two or three
hours (ammonia corrodes piano strings) or until dried, and when you do
play it you will be amazed as to how soft it sounds.  This process is
called "de-voicing".

If you do this and it still sounds tinny then someone has lacquered the
hammers or added that new voicing compound crap!  (A future story.)
The hammers at this point are _no good_ and must be replaced!

After de-voicing the hammers and they now sound like pillows, then
begins the next stage: re-voicing.

Factory Style -- Go to your laundry room and get the starch you use on
your shirts, etc.  Spray it into a cup and with a new eyedropper; fill
it up.  Use 4 to 5 drops maximum per hammer depending where you wish it
brighter and softer.  (5 drops for brightest, 3 to 4 drops for brighter,
1 or 2 drops for softer.)  Always allow at least 24 hours curing time.

For those of you who like a faster drying time, there is a tool my
staff is using now from Schaff Piano Supply called the "Electric Hammer
Head Smoothing Iron".  This is great for touch-up voicing as well.  The
Schaff ordering number is #909, Electric Smoothing Iron.  Or, if you're
an old-timer like me, use your Bunsen burner and the old style hammer
smoother.  I need to remind you, whether they're new or re-voiced
hammers, always note that the brighter the sound the faster the
breakdown of the fiber or flattening thereof.

Voicing a piano can be a lot of fun and it also can be your worst
nightmare!  I had a chance to see how factory voicing, stringing and
action work was done at the Baldwin, Everett and Steinway factories.
This is when some of the finest techs were still working.  This is
where my knowledge was learned and Thank God I knew these people and
can still remember the things I've learned.  Some of these things are
called "tricks of the trade" and never were written down so that others
could learn this stuff!  Anyway , it's out now!

Sincerely,
Kim Bunker