Dragon Oil

Dragon Oil, also called Dragon's Tear, is not actually an oil nor a tear. It's a somewhat mysterious magical fluid found in a gland in the guts of fire-breathing dragons. The gland, sometimes called a fire gizzard, is believed to be the source of fire-breathing dragon's flame, but it's difficult to get close enough to a living fire-breather and so it's actual magibiology is mostly speculation.

Procurement

It can only be procured from deceased fire-breathing varieties of dragons. The fire gizzard is removed and the Dragon Oil drained out.

Because the care, keeping, and killing of Dragons is regulated by the Ministry of Magic, Dragon Oil production and sale is regulated. A little oil goes a long way, so it's not a terribly difficult item to procure legally.

Uses

It's most common use is in Dragon's Balm, a healing salve, but it's property of magically permeating heat makes it useful in magical blacksmithing, or to control strong reagents in industrial level potion-making.