glass won't melt

[ryan-i]

has anyone else experienced this?.....

often times, when i pop open a hole in the flame thats perpendicular to the tube (never happens when opening a tube), i end up with a small "seed" of glass that seems to have the properties of quartz. it glows super white hot and will not melt into the rest of the glass. it happens just as the thin layer of glass pops open; i'll notice a bright flash, and then there is one of these seeds. it's the same as if you pop a hole off center, and your left with a tiny bleb of glass, only this glass seems to have completely different properties. i usually just pull it off w/ tweezers, but today it happened, and the seed went flying back onto my piece with a stringer in tow, and now i have this hair thin string of glass across the face of my piece that just won't melt in. the 4mm wall of my piece starts to droop, as this string just glows white and doesn't melt.:puzzled: anyone know what causes this?

[blazemaster83]

I have this same thing happen to me and it pisses me off. Seems to only happen on the most involved pieces at the worst time. I am certainly no chemist, but I have heard when you blow glass very very thin it changes the COE.

Im not sure if it poses any danger to cracking the piece, but it always looks like crap. The only way I have found to help this, is to not let the crap melt in. sometimes you have to jerk your hand out of the way quick, or it will melt into your piece even with the slightest flash. Then i just knock it off with tweezers, or pick it out with a 5mm rod.

[jusbag]

Helps to blow it out real thin then aim a hot sharp flame directly at it while blowing. Should help to keep that crap from flyin.

[davidwillisglass]

when glass is really thin it cannot absorb and move any of the heat from the flame to a cooler part of the glass through conduction, there is no heat sink for the flame and the glass overheats. getting so hot that fluxes etc are burned up and the chemical composition of the glass is changed. so if this now different glass is incorporated into the rest of the material it will not act the same.

pick or cut it out or in some other way remove it from your piece, or change your technique in order to not produce this. instead of popping the hole in the flame, you can puff a thin bubble, punty to the bubble and do a mini fire cut to the base and remove all of the super thin glass gently and carefully and leaving an open hole where the bubble was.

[kage]

i have no idea what any of you are talking about, but if your blowing bubble trash on your piece, then you are not popping the hole in the flame. what kind of glass are you using and what torch? sounds like your not getting it hot enough.

[Albino Sasquatch]

no hes getting it hot enough ive had this happen to its becuse your blowing it all out at once ive had less problems with it if i just blow it kinda thin then go bak in with the flame on it and pop it really fast this usually makes the piece of slag that wants to fly off and stick be a lot smaller or not there at all

[Riley]

that happens to me too. its usually on the lathe with the national in hand. it tends to happen less if i use a less hot flame for the pick n pop.

worse than anything is when it gets inside the weld and leaves that spot that never seems to even out.

or the ever so fun pop and pick whn the bubble bursts and spreads a thin layer of that reconstituted glass across a larger area, leaving small bubble funk.

good times.

[jello]

Had same issues on the lathe as well... trick i found to use.

Blow out thin without DIRECT heat. its a lathe trick i was tought, flash, blow, flash blow, it will thin out and you can pop the hole without even touching the glass with the flame, keep your flame just above the area where you want the hole. this is how i do seamless GONGs joints. its sounds different but give it a try, it works. (friend of mine worked at ROOR and he showed me how to do the trick, if you ever seen ROOR seams, they are the cleanest ive ever seen)

[Din]

Precicely what David Willis said. The glass breaks down and forms crystobolite, a different sillicate. This is actual devitrification (loss of the glassy state; crystallization). Picking it out is probably your best option.

[ryan-i]

thanks for the replies. I guess I was looking for a scientific explanation(thx David and Din) of what was happening, rather than how to avoid it. I don't have a problem with bubble trash or popping holes, per se - sometimes i just get rushed and work too hot and fast, and as albino mentioned, and I pop it at once rather than puffing out then popping. Except for yesterday, when the stringer stuck to my piece, it;s never affected the piece. It's usually about the size of a poppy seed on the lip of the hole. I just knock it off w/ my tweezers. I just want to understand the process.
btw, i have only noticed this with schott

[Uriel]

Thanks for all the replys too,, tried to rep you again Din,,, but I gotta share the love more...

[neddowerx]

I havnt had this happen in a long time, I don't blow my holes out thin though. I only blow out a small hole and then ream open to size.

[Brian Newman]

I guess I was looking for a scientific explanation(thx David and Din) of what was happening, rather than how to avoid it.

An old thread that may interest you:

www.talkglass.com/forum/showthread.php?1652