That's a very detailed explanation of some complexed connections and conditions.
I've seen some mentions of using iron filings, river stones, sand and what-not but nearly any resilient object will do. Its really just about gaining experience of the harmonies of internal and external alignments and intention. Striking a phone book for instance can lead the practitioner toward getting used to the feel of what it takes to break various objects without injuring self. A bag full of Mong beans and a good jow to loosen the tissues of the hand and wrist before and after is one of the best methods to start. I you want to get hard core then follow with sand and latter small stones but the beans or book are IMHO enough.
I meet
Master Grey in 2001 in Zhong Zhou and found him to be a nice guy and a clever conversationalist. Although he seemed very enthusiastic about martial art I did not get the feeling he had any real skill. I do not mean any disrespect by this, it's just that I know when I'm in the presence of a skilled practitioner and he lacked the vibe. I saw a couple of his students perform in the tournament and they were clearly out classed by most of the competitors there.
Bottom line is if you intend to pursue a regimen of hand conditioning be smart about it. Finding a good qualified teacher would be the best path to reach your goal. If that is not an option, research online and in books to compare various suggested methods and avoid the bizarre or extreme.
An old martial saying goes:
Twist the waist like a snake,
Root your feet firmly to the ground,
Be calm and patient,
Use your strength naturally,
Achieve your gung fu successfully.
These are good guide line for developing any martial skills.