Aramis Antiques has dated this piece to the 1850s.
The neck is slice cut in an ascending plain diamond design. The original matching stopper repeats the star engraving and the very top is cut with a circular band of 5 petal shapes, like a daisy, with a tiny central point. There is a good pontil mark on the base. There is a tiny black dot, like a black seed, in the base, which is an imperfection embedded when the decanter was originally made. The Greek key design suggests a very early Victorian date, c1850 or even a bit earlier, as that design was a popular Regency theme.
Aramis Antiques has dated this piece to the 1850s.
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