Blowing and or fixing glass

[AWvsCBsteeeerike3]

Weird subject and all but does anyone know how to fix cracks in glass cups? I have some rocks glasses that are probably 100 years old and somehow one of them got a crack that is really kind of neat. But, it leaks whisky which kind of makes it worthless as a rocks glass. Seems like it'd be possible to shove a bunch of stuff in there that's not toxic, good luck finding that in a glue store, and it'd work. But, I was hoping to melt the surrounding glass and somewhat encase the crack whilst making it water tight. No idea if that is possible.