How much C&D for 0 difficulty on hardest artifacts ?

Hi.
On the "50 to 0" difficulty C&D artefacts, like pearls, I've been at 1 difficulty for a while (from 225 C&D I think), and I was thinking, go for the 0 you can do it brave pilgrim.
I'm now at 300 C&D and still stuck at 1 difficulty on such artifcats
Someone knows how much I need please ?
I'm quite disillusioned atm I no longer want to advance further blindly.
On the "50 to 0" difficulty C&D artefacts, like pearls, I've been at 1 difficulty for a while (from 225 C&D I think), and I was thinking, go for the 0 you can do it brave pilgrim.
I'm now at 300 C&D and still stuck at 1 difficulty on such artifcats

Someone knows how much I need please ?
I'm quite disillusioned atm I no longer want to advance further blindly.