Pure oils vanish without a trace. Fake ones haunt you with a greasy ring.
Use uncoated printer paper or a coffee filter. Not glossy paper.
Put a single drop of essential oil in the center of the paper.
Leave it in a dry place. Start the timer above to track.
Hold paper to light. Any greasy ring or stain = not pure essential oil.
Your oil vanished completely. This indicates it's a pure essential oil!