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Author Topic: Iridisation of glass - can it occur naturally?  (Read 1642 times)

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Offline Pinkspoons

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Re: Iridisation of glass - can it occur naturally?
« Reply #10 on: September 20, 2012, 11:18:24 AM »
Long-term storage in dusty places prone to condensation seems to have a knack of causing iridescence to the surface of glass - I've bought old, but ostensibly 'new', glass from closed down retailers in Italy and Denmark in the past, and iridescence was present on quite a few pieces that had been left to their own devices for 30+ years.

I assume the dust makes water in the air stick to the glass longer than it otherwise would - items in more sheltered areas were unaffected. Also, being wrapped in paper exacerbates iridescence far more than glass left in the open - presumably as a result of the paper being more absorbent than dust.

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Offline Lustrousstone

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Re: Iridisation of glass - can it occur naturally?
« Reply #11 on: September 20, 2012, 11:25:45 AM »
Possibly because paper is quite acidic; acidic free paper is what conservators specify

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Offline Pinkspoons

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Re: Iridisation of glass - can it occur naturally?
« Reply #12 on: September 20, 2012, 11:30:20 AM »
This would also account for it.

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Offline David E

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Re: Iridisation of glass - can it occur naturally?
« Reply #13 on: September 20, 2012, 12:32:57 PM »
I've seen the combination of very light iridescence and gilding in Polish tableware.
That's interesting, except it is British glass :D

Thanks Nic for that thought, which could quite possibly be the answer. Old newspaper would certainly account for this and I suspect that's what was used. The iridescence is right up to the rim, so unlikely to be a liquid so, again, the wrapping could be the reason. I can't determine whether there is iridising on the inside though - very difficult to tell.

BTW, what are the metallic salts used to iridise glass?
David
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Offline chopin-liszt

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Re: Iridisation of glass - can it occur naturally?
« Reply #14 on: September 20, 2012, 12:41:51 PM »
I would strongly suspect different metals are used for different finishes - but I know that IoWSG sprays a lustre finish on using Stannous Chloride. (Tin)
This isn't an overly mirror-like shiny surface as some are, but somewhat matt.

I've got a "Balloon" vase, which has a layer of stannous chloride sprayed inbetween casings - it gives a subtle, slightly glittery, rainbowy effect inside.

In Wedgwood Fairyland lustre, the lustre can be a gold or green shade, Carltonware used a goldy red (on Rouge Royale), Zsolnay use an eosin glaze with a gold coloured lustre.....
Cheers, Sue (M)

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