Glass Message Board
Glass Identification - Post here for all ID requests => Glass Paperweights => Topic started by: Leni on January 30, 2009, 06:08:31 PM
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I have a whole cabinet full of Chinese 'Dime-a-Dozen' paperweights, and I have nothing against Chinese glass with regards to style, craftsmanship, whatever. But THIS is what I have against Chinese glass! :o These weights were last washed in warm water and vinegar just 18 months ago, and today I had to do the job again, plus wash the glass door and shelves and the mirror back of the cabinet I keep them in. Incidentally, it seems as if keeping them in the cabinet is what accelerates the reaction, as we have surmised when discussing this previously. (The only film on the ones I keep outside on the top of the cabinet is dust! ::) )
Funnily enough, the 'older' Chinese weights in my second picture were not affected at all, in spite of being in the same cabinet for the same length of time :huh:
However, the worrying thing is that a couple of the worst affected weights have developed bulls-eye 'bruises', in spite of not having been knocked, which would seem to indicate that there is an internal effect as well as the 'cloudyness' on the surface, which washes off easily :-\
I'd love to hear a proper scientific explanation for this!
Anyone?
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Covered in depth in the archive forum under 'Oily glass' I think.
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I've noticed that too Leni but not on all of my 'new' Chinese glass. One of the affected ones is a really neat pond scene with frogs. So far I have not noticed any bullseyes.
My main gripe with Chinese paperweights is when people try to pass them off as something else. I found a new millefiori in the store today. It has some canes that look more like Murano canes but with typical Chinese colours. I'd held off from buying any online because they asked too much. I got a nice deal on this one. It's a nice looking piece.
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Thanks, Frank :) Yes, someone has just pointed out to me that we discussed this at length here http://www.glassmessages.com/index.php/topic,13283.0.html
But I'm afraid I find the chemical information very confusing :spls: Did we decide it was damp in the air, chemicals in the wood, an unstable glass mix, or a combination of all three? :huh: And how does it affect the inside of the glass? :o
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Glasses which are batched with an excess of fluxes are prone to this reaction between the flux and atmospheric water. I have a Gillender Goose weight which has shown the same problem. Figuring I probably had little to lose I tried sealing the surface of the glass by spray painting it with clear Krylon acrylic paint. This has been remarkable effective. I did this years ago and I only recently noticed that the weight is showing a little haze. Previously I had to wipe down the weight every six months or so. This weight is kept in a cabinet in my basement so the humidity level is reasonably high year round.
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... an unstable glass mix...
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OK, I've just read through the previous thread(s) about this problem and found that Tom B from Ohio said, "It's caused by the glass manufacturers putting too much soda ash in the glass. For them, this allows the glass to be worked longer and cooler..."
And Sach said, "Glasses which are batched with an excess of fluxes are prone to this reaction between the flux and atmospheric water."
Can any glass maker or chemist say exactly why this makes the glass mix unstable, and what happens chemically to make it so? (Sach, what are the 'fluxes' you were referring to?) Knowing the actual chemical reaction might help with regard to finding a solution! Has anyone tried the idea previously suggested of moisture-removing silica gel crystals in their cabinets? Did it seem to work? I haven't got any, but would be prepared to try if it might solve the problem!
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Link in this post.
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OK, I've just read through the previous thread(s) about this problem and found that Tom B from Ohio said, "It's caused by the glass manufacturers putting too much soda ash in the glass. For them, this allows the glass to be worked longer and cooler..."
And Sach said, "Glasses which are batched with an excess of fluxes are prone to this reaction between the flux and atmospheric water."
Can any glass maker or chemist say exactly why this makes the glass mix unstable, and what happens chemically to make it so? (Sach, what are the 'fluxes' you were referring to?) Knowing the actual chemical reaction might help with regard to finding a solution! Has anyone tried the idea previously suggested of moisture-removing silica gel crystals in their cabinets? Did it seem to work? I haven't got any, but would be prepared to try if it might solve the problem!
Fluxes are chemicals which allow silica to liquefy / melt at much lower temperatures than it would other wise. In common soda-lime glasses the flux is soda ash (sodium carbonate). Lithium and barium are also sometimes used. Fluxes are highly reactive and corrosive chemicals which do just what Tom said , they make the glass melt at lower temps and they decrease the viscosity of the resulting melt. They also have an effect upon the Linear Expansion Coefficient, commonly referred to as the Coefficient of Expansion (COE). Over do the flux content and you can create a glass that is completely soluble in water.
The flux permeates the entire mass of the glass so no surface treatment will "neutralize" the problem. I'm still amazed the sealing the glass in acrylic paint was as effective has it has been. The only cure for this problem lies in making the glass properly in the first place.
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:D :clap: Thank you so much, Sach! :kissy: That is exactly what I wanted to know all along! And so clearly explained that even I can understand it! ;D :thup:
But how sad that there is nothing we can do to prevent the deterioration of the glass :( Oh well, I guess I'll just keep washing my Chinese paperweights regularly, and see how long it takes before they disintegrate completely! ::) :cry:
Thank you very much again, Sach :-* It's so nice to get a straightforward, uncomplicated explanation from someone really knowledgeable on the subject! :fwr:
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Its interesting to note that this seems to happen more frequently or perhaps is more noticable with paperweights than other forms. Interesting also that it's not just Chinese glass it happens with.
In previous discussions it was noticed that yellow colours are often involved when this occurs. I am interested in yellow glass of all shades and have one thick walled item which is oily and rather cloudy. How might yellow colour(s) tie in with the chemicals mentioned above ?
In yet another discussion, I seem to remember that the development of a very pale yellow colour in pressed glass over time could be associated with an excess of arsenic, ironically, originally used as a clearing agent.
Thanks
Pete
PS Incidentally, I can attest that Leni's home enjoys the benefits of central heating and double glazing which ensures that its warm and not at all damp, despite the English winter.
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this problem is not just with the Chinese. I was in a large showroom at a factory in West Virginia a few years ago and all their wares were suffering from this. Lots of stemware and assorted items, not paperweights. I have some paperweights from some American factories that have had this same problem. If the batch isn't right you can have lots of problems. A lot of the European factories have been buying batch from a couple of good sources for a quite a few years and have not been plagued with this problem. Batchmasters were always a very important part of the manufacturing "puzzle".
Many companies don't bother to keep their chemicals stored where they don't absorb moisture, hence when they batch the chemicals and they weigh it out they are off because of the moisture content in the chemicals that they don't calculate for when they are mixing their batch. Some suppliers of chemicals have higher moisture contents than others and can throw off formulations as well.
I heard Dominick Labino lecture on this to a group of studio glass artists about 25 years ago. He emphasized to make "good "glass. He was an extremely good glass chemist.
Tom Fuhrman