hammer heads

[Albertien de Pater]

Dear list,

Yesterday I serviced a Young Chang grand. I noticed the hammers had the
"tullip" shape of Steinway. Kind of parallelogram. There are many things I
would like to learn about hammers. Like which brands use which shape and
which felt. What is the effect of the different types of felt and shape on
the tone. How do you have to voice them. I learned the difference in
voicing between Steinway and Bösendorfer, but I don't really understand it,
see through it, so I can't apply this knowledge to any instrument. Choosing
the right type of hammers and shaping them in the right model, for one of
the other thousends of brands of piano's. 
Is there any literature on this subject? 

Thanks and regards, 
Albertien de Pater,
Amsterdam