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Author Topic: Oily glass - again!  (Read 2881 times)

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Offline Leni

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Oily glass - again!
« on: April 17, 2007, 01:49:49 PM »
I have just had to clean some of my paperweights because I noticed some of them were looking 'cloudy', and I found when I opened the cabinet that they were in fact not just dusty as I had supposed, but were covered with a sort of film!  I also noticed an unpleasant smell (which also got on my hands as I cleaned the weights, and is proving quite difficult to remove >:()

I remembered the subject of 'oily glass' being discussed here previously, and I found this thread in the Archives: http://www.glassmessages.com/index.php/topic,395.msg1934.html#msg1934

What was interesting was the fact that it was only the Chinese weights which were affected!  As well as all my 'dime-a-dozen' Chinese, I have in the cabinet a couple of Caithness flower weights, a Mtarfa, a Murano and a couple of Bohemian - none of these were cloudy at all! 

And the horrible thing is, the surface of the Chinese weights is actually beginning to show damage in a couple of cases!  There appear to be circular marks like the 'bruises' sometimes seen on paperweights which have been knocked or dropped, yet I know these weights have not been damaged in the time I have owned them, and definitely showed no such marks when I first bought them! 

I was particularly interested to read the post in the previous thread on oily glass where Frank gave a reference to a site which talks about the conservation of glass and the causes and effects such damage can have, and it would appear some of these weights are actually suffering a degree of devitrification.  I suspect this is as a result of being kept in a closed, albeit not completely airtight, cabinet. 
http://glassgallery.yobunny.org.uk/albums/userpics/10048/dime-a-dozen_cabinet.jpg

I was interested in the final comment in the thread, where Gareth says he found that proximity to Oak was a factor.  However since my cabinet is a fairly cheap modern (Chinese, again! ::) ) product, I think it more likely that humidity is to blame.  I say this because I have other Chinese paperweights, particularly the ones on the top of the cabinet, which have not shown this problem. 

I am posting this here rather than in the paperweight forum, because I feel it is a glass issue specifically, as it could obviously affect any Chinese (or other cheap, soda-based) glass! 

You have been warned!  :(
Leni


Offline Frank

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Re: Oily glass - again!
« Reply #1 on: April 17, 2007, 02:08:46 PM »
Oh dear. That will certainly sort out a few collections in time. Could you recognise the smell, did you try tasting?
Frank A.
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Offline Leni

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Re: Oily glass - again!
« Reply #2 on: April 17, 2007, 02:35:29 PM »
Could you recognise the smell, did you try tasting?
Youngest son licked one.  He said it tasted slightly salty, and bitter.  He also described the smell as "Horsesh*t" :-[ ::)
Leni


Offline Ivo

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Re: Oily glass - again!
« Reply #3 on: April 17, 2007, 03:21:00 PM »
The smell is vinegar, the taste is salt & the surface is sticky - it must be Chinese, Romanian or Crackle glass!
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Offline taylog1

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Re: Oily glass - again!
« Reply #4 on: April 17, 2007, 06:49:17 PM »
For me the smell is between vinegar and ammonia, surface sticky (haven't tried licking it yet !).
 
I've got two tall Nyman vases side by side, both geniune, and only one is oily - the one right next to the side of the old oak cabinet (which is an original fitted cabinet approx 100 years old). The one next to it (say 9 inches from the side of the cabinet) - no grease.
And thankfully no apparent damage to the glass.

As the cabint is on an outside wall, I can only surmise that the cold glass is causing something to condense on to it, but why only one vase is affected, the other shelves are fine - a complete mystery.

 


Offline Adam

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Re: Oily glass - again!
« Reply #5 on: April 17, 2007, 06:51:47 PM »
At the risk of being thought pedantic, may we please be careful with the use of the word "devitrification"?  This is the effect which can occur if glass is held at a high temperature (normally still in the furnace - much higher than annealing temps) for too long and crystals of various compounds start to form.  Crystals are of course not glass (hence devitrification or "de-glassing" to coin a word!).  This can be a serious defect if the crystals reach the finished article as they have totally different properties to the parent glass and therefore can set up huge stresses which are impossible to anneal out. "Devit" for short in the trade.  Importantly in the context of this thread, I know of no mechanism whereby devit can form at room temperatures - any crystals seen may be forming on the surface from whatever is leaching out of the poor quality glass.

Incidentally, CONTROLLED devitrification is how glass-ceramics are made.

Adam D.


Offline taylog1

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Re: Oily glass - again!
« Reply #6 on: April 17, 2007, 07:27:30 PM »


Offline Leni

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Re: Oily glass - again!
« Reply #7 on: April 17, 2007, 08:40:17 PM »
Wow!  That looks like it is the answer!  So 'Oak' is a bit of a Red Herring perhaps?  It seems as if any wooden cabinet is a possible risk, if the humidity / temperature etc. are right (or should I say wrong :( )   

As far as the smell goes, I wondered if there was possibly a combination of the smell of the chemicals coming off the glass combining with the varnished finish of the cabinet.  That's what it smelled like to me (whatever son may have thought  ::))

Adam; apologies if I used the word devitrification wrongly.  I picked it from the article in Frank's link on conservation of glass, possibly without sufficient care as to its meaning  :-[   
Leni


Offline glasswizard

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Re: Oily glass - again!
« Reply #8 on: April 17, 2007, 09:41:53 PM »
Leni, I have two Gentile paperweights that "sweat" if they are put in the curio cabinet. None of my other weights, including the Chinese ones do that. If I leave the Gentile ones out of the cabinet and just sitting in air, they are fine.
Terry


Offline aa

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Re: Oily glass - again!
« Reply #9 on: April 17, 2007, 10:38:41 PM »
http://www.rsc.org/chemistryworld/News/2005/September/26090501.asp
The article refers among other things to Formaldehyde, which is a constituent of most but not all MDF. If not properly primed, MDF can leach formaldehyde, so perhaps this problem could occur with MDF furniture as well as timber.

Doesn't sound as if licking affected glass is particularly advisable. :P ::)
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