How do you get a pumice so dagger can learn the ark summon? I can't find it anywhere.

First u need to get two pumice pieces and go to hades in memoria he'll only synth if u have beaten him. He's really not hard if u have the right abilities for each character.

You get one Pumice piece for beating Ark in the non-magic castle (can't remember the name) and either a Pumice piece or a Pumice for beating Ozma.

You get another pumice piece from the chocobo hot and cold

there are 4 ways to get teh pumice piece.

a)By defeating Ark in Oeilvert.
b)Chocograph Treasure - Chocograph #22: Outer Island 2.
c)In the Legendary Synthesis Shop.
d)Steal from Ozma.

there are 2 ways to get pumice

a)Legendary Synthesis Shop.
b)Defeating Ozma.