Strange as it may seem, when the first bluesmen experimented with playing slide on their guitars back in the twenties, they didn't use bottlenecks! The first slide guitar players utilized a knife, usually a pocketknife, or a straight razor--held between the ring finger and the pinky of the left hand. Held like this, it was possible to barre straight across the strings or play individual notes on different strings and then swing the knife--or razor--out of the way when it was not needed.
It sounded great, but it was clumsy--and painful! Soon bluesmen switched to a slide fashioned from a medicine bottle or made from the neck of a wine bottle. This worked better, it wasn't so uncomfortable, but it was just as clumsy--and the slide had a tendency to lay diagonally across the strings. Still, it was the only solution, so players used it.
NOW there is THE EDGE Slide from John Pearse.