I've been reading about the use of incendiary and flammable weaponry before the age of gun powder from the times of Mesopotamia , the Greeks, Romans, Persians, etc. Pretty impressive as anti personal and siege engines. Wonder why the forces of Mordor and Sauron didn't use them? Saruman had some kind of explosive. However, if they had added incendiary missiles to their catapults at Gondor, they would have burned the place down. Note, there were formulations that specifically attacked and cracked stone walls due to their chemistry. Was the war engineering of Middle Age - esp. the forces of the bad guys, behind that of our pre gun powder times? Did Middle Earth not have easily available natural resources, naphtha, oil, etc?

Sharps would probably know. Our folks used thousands of anti wall and anti personnel incendiary catapult missiles and grenades.