probably for spirits Chris, and either from a frame square or a tantalus - in earlier times known as a spirit square, I think.
Wooden frames, or a lockable tantalus, made to contain usually two or three identical bottles, with the plain lower undecorated part showing how far up the bottle the wooden gallery extended - below which you wouldn't have seen the glass so no point in taking the cutting right to the base of the bottle. For brandy, whiskey and gin etc.
You don't say if either the bottle or stopper have Nos. - I would have thought post 1850 (Regency examples tend to have a wide but shallow depression under the base, rather than a star like yours - but could also be later and into the C20 perhaps - there was so much copying. If there's evidence of matching Nos. I'd have thought more likely late C19 to early C20, but really not sure. You're lucky if there isn't any cloudiness.
The stopper has me confused - doesn't have the lighter more delicate lines of art nouveau - so either earlier or perhaps later and into the C20. If it does wobble then likely to be a replacement.
sorry the date aspect is rather vague.