Tack fusing un known glasses
Jo comments on tack fusing the bottle pieces. If you choose to do that, you have to have a very long and slow anealing schedule. Tack fused is much more difficult to anneal than full fused, as the pieces are not fully incorporated with each other and so try to act independently, leading to cracks and breakages.
When using glass of unknown compositions and compatibility, you really should check for stress. A highly stressed item is bound to break at some time in the future. A slightly stressed item can last for years.