It was said that ‘Tower Proof’ refers to the claim that it can be stored without detriment in the Tower of London for a year.
Gunpowder is, of course, a primary component of fireworks, and used to be made extensively throughout Britain. Like many British manufacturing industries it has disappeared today, but much remains as ‘visitor attractions’ or just sites which you may encounter on a country walk.
Accessibility of a port: two of the three ingredients were imported
The proximity of forests: charcoal – preferably alder or willow – is the third ingredient
Water: needed not only for the manufacturing process but also to drive the machinery. Hence centres of production were gunpowder mills.
An isolated location: in case of accidents and for testing of the finished product.