We need skill/spell that gives you an ability to analyze the vial you
have blessed. It might be automatic: When you bless vial the skill
tells you information about it like how good it is, is it unholy or not.
Of course we need a task which gives us higher % of that skill/spell so
that it works better.
Actually, there might be both that automatic skill and a spell with which
you can check a vial.

Bmoa the utter newbie