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Offline krsilber

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Re: lead glass
« Reply #50 on: February 24, 2010, 08:04:10 PM »
Thanks, David, for that snapshot in time of the development of lead glass and the part that Ravenscroft played in it.  Very interesting.

The sun-colored light block on that page look like they are of a bunch of different colors!  Blues and greens, not just purple or yellow.  Hmmmm.

I hadn't seen prisms used in a wall like that before.  Interesting.  I wonder how economical that would be to do today.

The Whitefriars bud vase you mentioned that glowed red - what color is it in normal light?

I wondered "aloud" in one of my posts about how the spectra of fluoro bulbs might vary.  This site shows examples of a few.  Particularly interesting is the CFB spectrum (which I think corresponds to what they call CFL) http://ioannis.virtualcomposer2000.com/spectroscope/amici.html#1daylightp

Quote
In a lead glass melt Mn color is very sensitive to oxygen concentration....

I suppose this would be an issue in any highly oxidizing melt, and its sensitivity to the redox conditions is why Mn was difficult to use.  Presumably the iron would be kept in an oxidized state, and the Mn3+ would have nothing to donate its electrons to, so it would make purple.  And being in the oxidized state, the coloring effects of the iron would be minimal, so there would be much to balance out the purple of the Mn.

"Manganese is
employed as an oxidizer to hold iron in the ferric state and as a physical decolorizer that absorbs
light very nearly complementary to that of iron, especially in conjunction with a trace of cobalt
oxide." (http://www.cwc.org/glass/gl965rpt.pdf)  Pages 29-29 further describe the decolorant actions of antimony, cobalt and selenium, and the role nitre plays, as well.

It must have been a real pain to change materials suppliers and as a result have to figure out the correct combination of decolorants to nullify the effects of whatever impurities were in them.
Kristi


"The most beautiful thing we can experience is the mysterious. It is the source of all true art and all science."

- Albert Einstein


Offline sph@ngw

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Re: lead glass
« Reply #51 on: April 06, 2015, 10:07:37 AM »
An addendum. 24% is the minimum level, as suggested, and Ivo's book (Glass Fact File A-Z, Miller's) mentions 65% content for glass used as radiation shielding.

Memo to oneself - always consult Ivo's book first. ;D

May I put this into a correct context?
In UK and EU law there is a legal limit defining "Crystal Glass" known as UK British Standard BS 3828  (1973)
Standard Number   BS 3828:1973
Title   Specification for crystal glass
Status   Confirmed, Current
Publication Date   28 February 1973  http://shop.bsigroup.com/ProductDetail/?pid=000000000000096400
Confirm Date   01 January 2012

You can buy a copy for 45 online from the BSI shop.

In it there are 4 categories of crystal glass (note in the US this does not apply. The term "crystal glass" means any glass that is crystal clear!)
1.Category 1. Full lead crystal containing over 30% lead oxide and meeting a density limit and a light limit.
2. Category 2. Lead crystal which must contain over 24% lead (except German pressed lead (Bleicrystal gepressd., which can contain 18% - I will explain later)
3.Category 3. Crystal glass containing potash, barium, zinc or lead alone or together of at least 10%
4. Category 4. Plain glass or verre sonore.

I need to get  the EU paper in front of me to give fuller details, but there is still an outdated legal definition.

Now there are many "lead free" crystal formulae on the mrket which mostly fall into category 3.
We have invented and patented a "non toxic lead free crystal glass", lighter than lead with no arsenic or antimony which "pings" just like lead crystal and can be cut and acid polished!


Offline Anne

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Re: lead glass
« Reply #52 on: April 22, 2015, 03:39:00 PM »
Does anyone have a copy of Neri's Art of Glass? I don't think I've ever seen a copy of it.Tenn. Tom

Still trying to find an affordable copy of that

Just picked up these two references to Neri's Art of Glass book, and wondered if you were aware that it's available as a scanned copy PDF download from the Rakow Library at Corning Museum of Glass? http://www.cmog.org/research/library-search


Offline KevinH

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Re: lead glass
« Reply #53 on: April 22, 2015, 08:32:54 PM »
If anyone wants a reference lookup from the Neri book, I have a copy.
KevinH


Offline sph@ngw

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Re: lead glass The Art of Glassmaking By Neri
« Reply #54 on: April 25, 2015, 02:02:44 PM »
Dr David Watts of the website Glass making in London has done a new translation of it and you can buy a copy for 15 +5 postage contact him via his website http://www.glassmaking-in-london.co.uk/

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