Molding glass

[AndreiRS]

I was trying to find around google if it is possible to melt the tip of a bottle to make it thinner with only a propane torch. But I just can't find anyone doing something like this. I just don't want to break the glass bottle trying because it is a nice bottle.

[Mads Barnkob]

Find a similar bottle and try on that first, just needs to be similar in glass type, colour, thickness or some thing like that. Glass blowers usually have a half circle of gas torches, maybe 5 or 6 sitting next to each other in a half moon configuration to get enough concentrated heat, so you might need more than a single torch to do it.

[AndreiRS]

I have not been able to find another like this, it has a lot of curver already on the design. But I will try with a common one, transperent glass, "white" or no color. Thanks man for the idea. If I manage to do what I want, I will post here the whole thing.

[futurist]

Propane torch is ok for smaller parts made of soda-lime glass, for working on bigger parts and/or borosilicate glass you'll need oxygen/propane torch
It would be nice if you could get didymium glasses for working on glass, they protect the eyes from harmful sodium glare and allow you to see what are you working on

[the_anomaly]

If the bottle is borosilicate, you can melt it with propane alone.  I use map gas and that does not burn at a much higher temp than propane.  You need a good torch though with a large flame, I've been using a Bernzomatic TS4000, not expensive and the local home depot / hardware store should carry it.

However, i'll bet the bottle is soda lime glass as this is popular for non cooking glassware.  With soda lime its the thermal shock that is the problem.  The bottle needs to be heated evenly.  If you youtube cutting glass bottles, you will see folks use string soaked in isopropyl.  They wrap the string around the bottle and light it on fire.  This produces thermal shock just where the string was wrapped.  Drop the bottle into cold water and it will (usually) crack on the line.     

Maybe you can use a small fire to heat the bottle up close to the softening temp (900C?)?  The idea would be to submerge the bottle in the same temp so it heats evenly.  Coal will get there without extra O2.  Wood will work but you will need a fan.  If you try the fire, skip the torch all together.  Don't bring a bottle of propane near open flame or it could explode...

If you try it, make sure to wear protective clothing and good safety glasses.  If it shatters, you will have hot glass fly at you.