I will go for an olive oil quench (instead of water) both because it's a mystery steel, and to avoid breaking the blade, as such double edged blades are prone to. Then temper, polish and retemper-heat color to a purplish black, as that is the color an Athame is supposed to have.
I am currently struggling with the shape of the hilt (again fashioned from a piece of Iroko hardwood I found somewhere), trying to give it some organic shape, inspired by master knife maker Gerhard Wieland. By the way if you want to take a look at his incredible work try http://www.wieland-der-schmied.de/03_1_messer.html.
