How can I melt a beer bottle into an ashtray without it breaking in an open fire?

With great difficulty! Slumping glass [where you change its shape without melting completely] requires controlled heating and cooling. This is very hard to do with a gas torch. You could try burying the bottle in sand and building a fire on top and letting it burn slowly ie; like a charcoal fire. Over time it could "slump" Legend has it that this was the way glass was discovered. Sand contains Silica, a component of glass.Best of luck!

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How can I melt a beer bottle into an ashtray without it breaking in an open fire?

I've heard it can be done on an open fire.

Beer Bottle Fire Pit

The reason the glass breaks is because it heats too fast, or it heats unevenly (look up glass COE), or doesn't get properly annealed. The key is to heat glass slowly (ramp phase), till you get the desired shape. Heat the glass all the way around (like in a sealed chamber). Hold the glass at a specific temp (soak phase). This temp varies with most slumping occurring at about 1300-1410 degrees for around 10 + mins. Then you need to turn off heat and flash vent till you get to about 1100 degrees. Once the temp holds to 1100 degrees leave temp off till it cools to 955 degrees naturally. You need to hold the heat at 955 degrees for about 15 mins. This may require you to add a little heat to keep it from dropping too low too quick, (anneal phase). The anneal phase is extremely important to prevent thermal stress fractures. Once you have completed the anneal phase, you can remove all the heat, without opening the chamber, until the glass cools completely on it's own. DO NOT PEEK at your glass piece until it is completely cool. No matter what the glass has done, there is nothing you can do at this point to change it now. If you open the chamber before it is completely cool, it will undoubtedly cause your piece to develop thermal stress fractures and break, if not immediately, in will in time. As you can see, you will need a thermostat for proper glass slumping, as it is seriously a science and can cause serious popping and flying glass. Your best bet is to do some research on kiln fired glass to understand the temps of the different stages of glass melting and annealing. We in the hot glass business call this a firing schedule. Good luck and might I suggest wearing eye protection and a leather apron if you plan on doing this on your own in an open pit. There is nothing like hot glass exploading and hitting your flesh. It sticks like syrup.

I seriously doubt that you could get a fire hot enough on a small scale. Did you try a flame working torch? If you go to the website for Corning Museum of Glass www.cmog.org they probably have pictures of things and maybe for sale. They can at least give you the answer that you need if you write to them.. Good luck!

Perhaps using a propane torch very slowly circling the bottle, allowing it to melt.

So I also wanted to know this answer so I just actually did it and this is what I got from it

This is a glass Heineken bottle

Use MAP gas, it's hotter than Propane. And maybe some gloves and tools wouldn't hurt, either!!!

try a kiln