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Antique glass funnels are far from rare, but antique glass funnels made specifically for decanting wine are quite the opposite - they are seldom seen. The difference between the frequently seen models and a funnel made for decanting wine, is that it has a curved or cranked spout to send the wine gently down the wall of the decanter rather than dropping straight to the bottom of the decanter and becoming over-aerated.
This is a small example. Many glass wine funnels have been very slightly reduced as most glass funnels become chipped at the spout; this one seems to have escaped that fate.
The similarity of shape between a wine glass and an up-turned funnel allow a dating to be well assessed, and it can be seen that the shape of the bowl closely resembles a wine glass of the period.