Here's a look at the notes that artist Franz Vohwinkel had to work with from our creative team:
Color: None (Artifact)
Location: Not important
Action: Show a close-up of vial of noxious purplish-black liquid. A female rogue's leather-gloved hands are about to unstopper the liquid (but she's mostly out of frame -- keep focus on the vial itself). We can see skull-like shapes in the swirling liquid.
Focus: The vial of magical poison
Mood: One drop and you're dead.
So, I've looked at this art a number of times from flipping through the Player's Guide and when I've seen the card in packs while drafting but my brain had never progressed beyond simply seeing a purple swirling fluid in the vial. Turns out that those are little skulls in the vial!
Take a look for yourself.
And here's the initial sketch concept he submitted: