Every hunter in the metropolitan area knows that rainy nights are when the borders between domains get thin. But not every puddle of stagnant water is a sign of supernatural intrusion, and mistaking mundane industrial runoff for demonic residue can waste precious tracking hours. To survive the streets, you must learn to read the chemical signatures hidden in the city's grime.

The Slick and the Shine

Standard oil slicks produce a rainbow sheen that floats neatly on the surface of rainwater, shifting colors as the angle of light changes. Supernatural residue behaves differently, sinking beneath the water line and clinging to the concrete like a greasy, dark oil that resists evaporation. It carries a distinct iridescent amber hue under neon light, glowing faintly even when the streetlamps flicker out.

If you touch it, the substance feels cold to the skin, almost like liquid ice, despite smelling faintly of burnt copper and old battery acid. This temperature inversion is the definitive indicator of a recent materialization.

Testing the Threshold

Carry a small vial of silver nitrate solution in your coat pocket at all times. Dropping a single bead of silver into a suspected puddle will cause an immediate, violent effervescence if a manifestation occurred within the last three hours. If the reaction is silent, you are simply looking at municipal waste, and your target has already moved to higher ground.