How is it possible to heat glass tubing hot enough to be bendable without burning your hands or requiring protective gear?
I’ve seen some clips on American Restoration of folks making neon signs, and they’re holding glass tubing bare-handed while they dip it in the torch flame. I know glass is a pretty good conductor of heat, so shouldn’t their fingers be blistering by the time the glass becomes pliable?
Glass is actually a poor conductor of heat.
Glass isn’t a good conductor in the sense you’re thinking about.
All (most) of the heat is simply gone by the time the distance is travelled.
in case nobody mentions it, glass doesn’t transfer heat well.
it depends on the size of the glass, the more of it there is the hotter it needs to get and the larger the flame, both the flame and the glass radiate heat.
with small tubing you can be inches away.
I don’t have a cite but I think glass is a poor heat conductor.
Don’t they teach this in Chemistry class anymore?
We used to have to bend our own tubing.
Yes, you can bend glass with your bare hands. I have done it many times. Just don’t touch it too close to where you’ve heated it up. By the way- glass hot enough to burn severely looks just like cold glass, and doesn’t cool off all that quickly.
Is that what they called it?:dubious:
We did it in 6th or 7th grade. A 8 inch or so piece of what was probably quarter inch glass tubing. Heat it over a Bunsen burner until it was red in the middle and make a little 90 degree bend. Only only one person manged to splatter hot glass on his arm. I don’t know if he was bending it towards himself or it it came from someone else, but it wasn’t hot enough so it broke and the hot glass landed on his arm. Okay, so ‘splatter’ probably isn’t the right word.
Ya know what else does that…copper fittings. I’ve picked up copper fittings that I soldered 10 minutes ago and had to put them back down since they were still way too hot to handle.
:smack:
Whaddaya mean, heat it first?
Personally, I concentrate X-Ray vision for glass bending, but I like to bring everything down to layman’s terms when I’m speaking to the unwashed masses.
I don’t know the answer to the OP but it’s certainly not because glass is a poor conductor of heat.
Glass has a thermal conductivity roughly equal to that of concrete, yet stepping on concrete while barefoot on a hot day is quite painful, even though it’s nowhere near as hot as glass that’s been heated to the point where it has become pliable.
Huh?
glass can hold a lot of heat but not transfer it well through itself. that is part of why thermos bottles can work.
But stepping on that part of the sidewalk that’s in the shade won’t be uncomfortable at all.
You don’t touch the hot glass. You touch inches away from the hot glass, which is actually cool because glass is a poor conductor of heat (cite).
There are some substances which are even worse conductors, and where you can touch a red-hot object without burning yourself. See here (technically, you still aren’t touching anything hot–a very thin layer at the surface cools immediately and the poor conduction prevents any more heat from replacing it).
You don’t know the answer because you don’t understand the problem. 
Yes, concrete - like glass - will get hot if heat is applied directly to it.
Also like glass, it does a rather poor job of conducting that heat to adjacent areas that have not been directly heated. Thus (as aktep notes) you can step on a portion of the concrete that’s in shade but near the sun-heated part and find it quite comfortable.
A very, very small part.