Topic: Look what happened to my glass!

[Adam]

I've been offline for a couple of weeks and I've just noticed comments here about bubbles supposedly expanding and causing breakage.  I cannot understand where this one originally came from as it cannot be true.  Consider the moment the bubble was formed.  The glass is still very soft (or the bubble wouldn't be round) and therefore at a very high temperature.  Any gas in the bubble is at that moment at ambient pressure.  The glass is then cooled and the gas contracts resulting in a very low pressure in the bubble by the time the glass is sold.  At any time in the future if the glass and its bubble were heated the temperature rise needed to increase the pressure in the bubble above ambient would be such that the glass would be molten and the house would be well alight!

As a defect in glass, a bubble (unless of course so near the surface as to be easily broken to leave a jagged edge) is of cosmetic significance only.

Adam D.

[krsilber]

I've thought about that, too.  But could it be that the glass isn't completely gas impermeable as it's cooling?  Or that it somehow draws gas from the glass?  Otherwise wouldn't things like hollow candlesticks and stems be under enormous pressure after such a large change in temperature?  Seems like the least weakness or damage would make them implode.

I agree with you that small bubbles in glass are not likely to be the cause of structural failure, even with change in temperature or pressure.

[aa]

I don't know whether this helps but I have heard that Elvis is alive and well and living on the moon. Which leads me to the hypothesis that the bubbles are incubation cells for aliens and at high altitudes they are able to burst out, rather like a chick breaking out of an egg. Of course this results in the glass cracking.

[krsilber]

Good reason not to ship by airmail!

[heartofglass]

I have had this self-destruct phenomenon occur with 2 pieces of glass over the years, the first nearly 20 years ago in my very early collecting days. It was a very thin, almost scientific looking bulbous vessel, & it developed a perfect division between the neck & body/bowl of the item quite spontaneously. It was on a windowsill (sorry, but I was young & foolish then!) & it basically cracked & collapsed. I have no doubt now, in retrospect, that it suffered from extremes of temperature.
Second one was more recent, a Nason style vase black with aventurine spatter. That was less dramatic, however. I had owned it for a couple of years & one day I noticed a crack (which has "held") all the way through it.
It was not on a windowsill, but it was in a room that undergoes severe temperature changes from our greatly overrated climate. That is, variants of up to 35 degrees C. or more between summer & winter. The room has a flat, skillion roof with probably no insulation.
I have bought loads of glass that has been sent via air mail, all of it has survived the long haul flights except for a couple of pieces which suffered more from very poor packaging than altitude stress. In fact I shipped a fair bit of glass back from my 2003 trip to France (a paperweight) & England (several vases & a Murano cigarette lighter) in my hand luggage! No problems there!