### Clue: Hard material Sir Henry for one first demonstrated? (9)
### Answer: SATINWOOD 
 ### Explanation: Definition: Hard material
 WOOD(a famous example; for one, was Sir Henry, English conductor, famous for conducting the London Proms) **placed below**(first …, in a down clue) [ SAT IN(past tense of "sit in";to participate in a demonstration;an act of civil disobedience, involving sitting).
Answer: The hard wood from the tree of the same name.