Thanks. I don't know about common knowledge. I was trying to see what others had to say about it.
Gleason sensei talks about the palm being earth. He shows hand of fire and hand of water, etc. It is crystal clear when he shows it. I copy him and it all makes sense. 10 minutes after I walk out of class I think - which hand orientation was "fire"? I assume I have a mental block about it. I was hoping a few other perspectives would help me over my mental barrier(s).
Palm = Earth ( I use "ground") - I guess I would tend to agree from my limited understanding. As for hand of fire, water... etc. this corresponds to something I have mentioned before in other threads, that being that there is both a physical and non-physical component inherent in the waza. The hand aspect is only the physical manifestation. There is also an associated visualization (chinkon-kishin-no-gyo), associated mantra (norito-no-gyo), powered by a corresponding elemental kotodama form (kotodama-no-gyo [gokui]) that is also simultaneously applied. n'est-ce pas?