The phrase "Flash in the pan" explained

The flash pan or priming pan is a small receptacle for priming powder, found next to the touch hole on muzzleloading guns.  A small amount of finely ground gunpowder is placed in the flash pan and ignited. The flash of flame travels through the touch hole igniting the main charge of propellant inside the barrel.

The ignition of the main charge from the flash pan was not a guaranteed operation, however, and sometimes it failed. In those cases the spark would flash in the pan, but the gun would fail to fire. This led by the end of the 17th century to the expression “flash in the pan” to mean a failure after a brief and showy start, or momentary sensation of no real importance.