The Source
The sand, worked at the fire door's edge — the vial of the alchemist, the lens of the light school, and the one the serpent-folk distillers set their venom in.
The Yield
A beach gives a season's sand; a season's sand gives a vial's worth; a vial's worth gives the address.
In the Workshop
The glass is the vessel of the crossing: the venom is the delivery, and the glass is the one who holds the delivery until the hunter points it — the address in a vial.
Cost band: journeyman (the vial is the guild mark) — on the ladder in The Maker's Hand, the material is the floor, and the floor is the one the mine or the marsh or the tree has to give. Recipes that take it: distillation, alchemy