Venetian glass necklace

So these are the 'before' pictures:
I had to rethread this necklace after I took the pictures.
It clearly was well loved and cared for.
One bead had at one point been broken in two, but somebody had put lots of time and effort restoring the bead and making it useable with glue.
So when I rethreaded it I could see the way the beads were made: they are all a little different in shape and pattern. Inside the beads are completely black and the white dots are only on the upper layer.
The man who made these beads must have spent lots of time making them.
I added another, more simple lock, as I think the one in the picture was not original to the necklace.
So when do you think this necklace was made?