Stretching a glass bottle neck is one of the techniques glass artists use to create art from soda, beer or wine bottles. While the process involved in stretching a glass bottle is not a difficult one, it does require patience and equipment that is generally too expensive for the casual hobbyist. If you have access to a kiln or experience with a blowtorch, you can turn empty glass bottles into individual works of art suitable for collecting.
Spray the neck of the bottle with devitrification fluid to ensure the colour of your glass stays the same as it stretches. You can purchase it at a craft or hobby store. Skip using this fluid if you want to intentionally use the discolouration of the glass as an artistic expression.
Hang a glass by its neck from the top of the kiln. Use a wire hangar looped around the neck of the bottle to achieve this. The bottle should be as high as you can set it, allowing plenty of space for stretching. This will keep the bottle secure and allow it to stretch under its own weight as the heating process begins.
Set the kiln temperature at 260 degrees C per hour. When the kiln reaches 593 degrees C, turn off the heat for 10 minutes, then set it to 121 degrees C and continue the heating process until the heat inside the kiln reaches 704 degrees C.
Increase the heat of the kiln gradually. You can increase the heat at any rate you want during this stage, stopping when the neck of the bottle has stretched to your liking or until the kiln reaches about 760 degrees C.
Open the kiln and allow it to cool to 593 degrees C. This allows the glass to begin cooling without becoming cloudy or discoloured. The technique is called annealing. Once you have cooled the kiln, turn it off and allow the glass to cool to room temperature on its own, then remove it from the kiln.
Since a kiln can be quite expensive, you may want to look into renting time with a kiln at a ceramic or craft shop that specialises in working with art that needs to be heated.
Always be cautious when handling heated glass. Wait plenty of time to ensure it cools and use gloves to be on the safe side.