I've just checked a Harbridge confiture and a Tudor confiture.
The Harbridge has nicks that
turn out to be heart shaped around the rim, just like this celery - with a line down the middle.
It's been done by cutting twice. It just turns out heart shaped because of the curve of the glass and the edge.
The Tudor has a ring of curved cuts - no line down the middle where two cuts meet.
Both sets of cuts render the confiture unsuitable for drinking champagne.
