Tuning Steinway Verticals

[Ed Sutton]

Jeff wrote-
> However, new ones?  Last new ones I tuned had tuning pins so tight the
> casters would come off the floor when you pulled the tuning hammer.  Then,
> there's the "surprise" pins!  (you know, the ones where you get ready to
> pull hard, you hear "snap!" and all of a sudden the pitch has jumped a
> major third?)
> 

Which makes me wonder: What is the pinblock material? 
Ed