All Glass Gravity Bong Here's how to make a glass gravity bong at little or no cost. You'll need a large glass bottle (this can be done with any size bottle, however larger bottles work much better for a GB) and you need to cut the bottom off it. I used a 1.75L wine bottle, which worked well. You can watch the video (which is 10 min and boring as shit) or follow these simple instructions. 1. With a glass cutter, score the circumference of the bottle, about 1/2 inch from the bottom. If you want a smaller bong, simply score the bottle higher up. All you you need is a complete score, usually just 1 pass with the glass cutter. 2. Boil some water. You're going heat up the bottle so you can thermal shock with it cold water, the shock causes the weakest part of the bottle, the score, to crack and everything below it too fall off. Once you have boiling water, or at least very hot water, pour it slowly over the score line while rotating the bottle. Now turn on the cold water and run it over the score line. The new edge on the bottle is pretty sharp, so I suggest sanding/filing enough to dull them. Rinse the bottle out afterwards. If the bottom has cracked but not fallen, try gently tapping it. If no cracks are visible, repeat the hot water/cold water cycle 1-2 times. You don't have a deep enough score if it still doesn't crack. [ame="http://www.youtube.com/watch?v=sFXngPx3w3M&feature=player_detailpage"]YouTube - Wine Bottle Cutting 30 seconds Perfect Edge Bottle Cutter GreenPowerScience Bottleneck Guitar Slide[/ame] $3 glass cutter from any hardware or craft store works just fine unless you want those perfect edges for your gravity bong. 3. Find a bowl. 19mm bong bowl fits well. If you don't have a bong slide there's nothing stopping you from improvising. The most airtight solution I found was with the generic slide/stem combo put inside a hollowed out cork. This is mine. Fits nicely inside a half gallon pitcher.