Topic: lead glass

[krsilber]

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

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.

[sph@ngw]

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.

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!

[Anne]

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

[KevinH]

If anyone wants a reference lookup from the Neri book, I have a copy.

[sph@ngw]

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/

Mod: email address removed to prevent spam harvesting and replaced by site link

[oldglassman]

Hi ,
             I have just been re reading this interresting thread and thought that this article may be of interrest to those who have commented here on the subject of  lead glass development in England , (scroll down to read full article)

http://www.academia.edu/7121691/Late_17th-Century_Crystal_Glass_An_Analytical_Investigation_Dungworth_and_Brain_

I am told by Colin Brain that more publications are in the pipeline but not yet available for public viewing.

cheers ,

Peter

[rabugheida]

The way that i can be fairly sure that the glass is crystal is because of the work that was done on it

I believe that the addition of the lead greatly increases  the time one can work on a piece

so if there are intricate cuts it is most probably crystal

anyone?

[sph@ngw]

Hi,  Another way to tell is by " pinging it "  ...........  Vases , bowls and drinking glasses have a sustained bell like ring.
 Regards Patrick

I have to disagree.
Our new World First glass, non toxic, totally lead free, has a wonderful ring if you "ping it"!
The shape of teh glass bowl also counts for much of the ring-sonority.
The only real way is a chemical analysis using professional techniques to analyse a tiny sample.

[sph@ngw]

None so queer as folk. The recognised inventor of lead crystal glass stemware is George Ravenscroft, a (GR)s proved by Dr David Watts, who analysed several Ravenscroft glasses, and found that he gradually added more and more lead until around 35%! there is a chart showing this somewhere in the Glass Circle records
he was NOT the first to add lead to glass, to soften the batch and make it easier to use.
GR was financed by the Worshipful Company of Glass Sellers Co of London who paid for two chairs of makers in Henley on Thames, easy to ship to London, according to my copy of Hartshorne's "Old English Glasses" p 240.
His patent is dated 16th may 1674 (Andy please note) but he probably had made it a year earlier in 1673! The glass Sellers were establish in 1664 so celebrated 350 years in 2014!
Even the Portland Vase overlay (Roman 1st century) has a very small amount of lead that allows easier cameo carving!

[sph@ngw]

The way that i can be fairly sure that the glass is crystal is because of the work that was done on it

I believe that the addition of the lead greatly increases  the time one can work on a piece

so if there are intricate cuts it is most probably crystal

anyone?

"work on the piece", in fact means working hot glass for up to 3 minutes, without it going solid on you. Soda lime glass goes solid after about 1 min 10 secs!

The cutting is usually only done on lead glass as it is softer to cut, and to "brush polish" or more recently "acid polish"!

Also lead crystal has the refractive index of over 2.45 so it sparkles like a diamond when cut and polished well Just wanted to clear that up.

Mod: Edited to lift the response out of the quote.