"DanR" wrote
| It is black, and fairly glossy. However, it is neither water or spirit
| based paint - when you rub the surface with a damp cloth fairly
| persistently, it comes off! (Testing this has not helped the decorative
| order, mind you...) It doesn't look like any sort of paint or varnish,
| in fact.

Blacking? As used for grates etc. More likely if your bannisters are iron.

Owain