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Glass Discussion & Research. No ID requests here please. => Germany => Topic started by: paradisetrader on November 06, 2005, 02:44:38 PM

Title: Conchoidal fracture (bruise) on Greta Vase
Post by: paradisetrader on November 06, 2005, 02:44:38 PM
I think the fault / damage seen on this large Greta Vase is a burst bubble.
I'd like to confirm that and make pics permanently available for future reference at the Glass Queries Gallery generously provided by Anne (Yobunny) http://glassgallery.yobunny.org.uk/thumbnails.php?album=37

Something Frank said in an earlier thread was in the back of my mind when I thought this but reading it again now I am unsure.
In topic Factory Faults (http://www.glassmessages.com/index.php/topic,2240.0.html)Frank said
Quote
Bubbles near the surface easily crack and sometimes a hole to small to see even with a glass. Water has much better eyesight and has no trouble finding its way in where it evaporates when warmer with some of the vapour leaving the way the liquid got in. In doing so it leaves behind a deposit of the heavier minerals giving the whitish frosted appearance."

This bubble is entirely enclosed within the glass. No crack can be felt on the surface only a very very slight bump ...possibly. I guess there may be tiny cracks too small to see or even feel.  The frosty area around the bubble seems to me more to do with internal shattering of the glass rather than mineral deposits. The frosy area is not a perfect circle around the bubble.

Frank also said
Quote
There is no way to tell if a crack in a bubble was caused during cooling, annealing or after the event.   
I'm not sure exactly what it meant by this but if still refering to burst bubbles then I have the stongest feeling that this particular one was done after manufacture ....probably by me, by leaving the vase on a sunny window still, possibly after washing it.

The vase is destined for a place where it will be much appreaciated desipite this burst bubble which only shows from one side.
Title: Conchoidal fracture (bruise) on Greta Vase
Post by: Connie on November 06, 2005, 03:07:38 PM
JMHO Peter - If the bubble is still completely enclosed by glass then it has not burst.  It has the potential to burst as Frank described so moving it where it does not undergo aburpt temperature changes is a good idea.

A burst bubble will either have rough edges - the whole top of the bubble shattered off.  OR - it can have a small hole on 1 surface as previously described.
Title: Conchoidal fracture (bruise) on Greta Vase
Post by: Frank on November 06, 2005, 03:11:08 PM
The hole can be microscopic and undetectable.
Title: Conchoidal fracture (bruise) on Greta Vase
Post by: Connie on November 06, 2005, 03:16:48 PM
Ok Frank  I revise my opinion.  The bubble has not burst in such a way that it is visible to the naked eye  :lol:
Title: Conchoidal fracture (bruise) on Greta Vase
Post by: paradisetrader on November 06, 2005, 03:53:43 PM
So it this is a burst bubble then ?
Title: Conchoidal fracture (bruise) on Greta Vase
Post by: glasswizard on November 06, 2005, 04:20:18 PM
Peter I would have to say if the bubble is entirely enclosed in glass then it has not burst yet. Terry
Title: Conchoidal fracture (bruise) on Greta Vase
Post by: Frank on November 06, 2005, 06:42:16 PM
Quote from: "paradisetrader"
So it this is a burst bubble then ?


Probably. There is a slight possibility that the contaminent that caused the bubble is not one usually used that would vaporise completely, as a result it only partially vaporised and left residue - but I consider that highly, highly unlikely.

You could check it out with a 30x magnifier but that might not be strong enough. Put it back in the window and see if when hot the water forms droplets. Hmm winter.
Title: Conchoidal fracture (bruise) on Greta Vase
Post by: paradisetrader on November 06, 2005, 07:25:38 PM
What I absolutely want to avoid is it getting any worse Frank, as it is already promised, so I won't be trying that
I just want to learn something from it before I pass it along.
Looking again more closely with a jeweler's loop I see the whole thing is fan shaped with several fine lines describing the curve of the fan and parallel to that.
Light is reflected particularly brightly from one spot which I took to be the bubble but maybe not, or perhaps a collapsed bubble.
I am beginning to wonder if it is a "bruise", an internal crack, perhaps focussed on a point where there used to be a bubble.
I shall try to get better pics of if in the next day or two, but it's not easy as I have no macro function on my camera which would require a converter to the lens for that.
Also the fault is only clearly visible from the inside as it lies underneath a thick rib in the pattern which distorts it.
Title: Conchoidal fracture (bruise) on Greta Vase
Post by: Connie on November 06, 2005, 07:55:15 PM
Peter -

Try putting your camera to your loupe over the area. I haven't used theat technique myself but some others on the AB board used that technqiue when they couldn't get a close enough shot on some detail and the results were amazing.   8)
Title: Conchoidal fracture (bruise) on Greta Vase
Post by: Cathy B on November 08, 2005, 06:54:13 AM
Would you be able to take precise measurements, height, across the top and number of ridges in the frosted section?
Title: Conchoidal fracture (bruise) on Greta Vase
Post by: paradisetrader on November 08, 2005, 09:41:15 AM
Cathy thats not a favour at all
Height is 20cm, width is 30cm
Reeds in frosted section =5
Title: Conchoidal fracture (bruise) on Greta Vase
Post by: paradisetrader on November 16, 2005, 03:30:38 PM
New pic with the aid of a magnifying glass
Not very good but the best I can do ...
It measures about 1cm across
(http://glassgallery.yobunny.org.uk/albums/userpics/10006/PB131222.JPG)
and Im now thinking its a "bruise" but still not sure.......
Title: Conchoidal fracture (bruise) on Greta Vase
Post by: Connie on November 17, 2005, 02:48:30 AM
FWIW  - It looks like a bruise to me.
Title: Conchoidal fracture (bruise) on Greta Vase
Post by: Frank on November 17, 2005, 06:05:12 AM
Seconded
Title: Conchoidal fracture (bruise) on Greta Vase
Post by: Ivo on November 17, 2005, 08:06:41 AM
"Three independent forensic experts have confirmed"....
Title: Conchoidal fracture (bruise) on Greta Vase
Post by: paradisetrader on November 17, 2005, 10:59:16 AM
Thank yopu all
The striations can only be seen under magnification - otherwise it just looks frosty - which is what threw me off.
It seems odd that a knock can do this without cracking the surface. Just another of the many mysteries of glass !
Title: Conchoidal fracture (bruise) on Greta Vase
Post by: Frank on November 17, 2005, 07:19:55 PM
Not really, the ripples are a shock wave.
Title: Conchoidal fracture (bruise) on Greta Vase
Post by: KevinH on November 17, 2005, 08:44:09 PM
... and "sub-surface bruises" are often seen in the sides of paperweights.
Title: Conchoidal fracture (bruise) on Greta Vase
Post by: aa on November 18, 2005, 06:27:35 PM
I believe the correct term is conchoidal fracture :D
Title: Conchoidal fracture (bruise) on Greta Vase
Post by: pamela on November 18, 2005, 06:39:37 PM
aa: great post - I LOVE languages and this is reading it square:
conch - Muschel (the most expensive pearls by the way)
bruise - break: Bruch
conchoidal - muschelig
everyone understands German this way - mother of pearl breaks
'muschelig'
Title: Conchoidal fracture (bruise) on Greta Vase
Post by: paradisetrader on November 18, 2005, 07:23:08 PM
Quote
conchoidal fracture

Thank you Adam
Yes that seems to be it alright
Quote
A conchoidal fracture has curved lines, rather like a sea-shell (which is where the word "conchoidal" comes from). Obsidian has conchoidal fractures, as does ordinary glass.
http://www.gwydir.demon.co.uk/jo/minerals/obsidian.htm

I'm glad it translates easily into German for you Pamela  :)
Title: Conchoidal fracture (bruise) on Greta Vase
Post by: pamela on November 18, 2005, 08:55:23 PM
aa:  :D
Peter:  :D
obsidian is glass 8)