I know that when you reroll an ethereal item with the SOJ + P skull recipe it can turn the ethereal item into a non ethereal one. My question is, can you turn a non ethereal item into an ethereal one with the same recipe? Or does it just keep rolling non ethereal?

Will keep rolling non-eth.

Only way to get eth rares is drop or charsi imbue

Thank you for the info sir!

This. Sadly