Glass Message Board
Glass Identification - Post here for all ID requests => Glass => Topic started by: kazmusic on March 05, 2007, 05:41:31 PM
-
Can anyone tell me an easy way to tell lead crystal glass from regular glass?
-
Welcome to GMB.
Weight is one of the first indicators! 8)
Sometimes it has a very, very light grey tinge - barely detectable. I believe 24% is the minimum acceptable quantity to properly qualify it as "lead crystal", but many companies would add much more than this. Not sure what the top limit is, but 35%, perhaps?
-
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
-
33% always used to be the UK "full lead crystal" norm, with the 24% used on the Continent rather disdainfully called "semi-crystal". All figures are expressed as the oxide, PbO.
I have seen 92% reported, with a density the same as cast iron. Specialised optical use, I believe, and I think has a brownish tint - not very attractive no doubt!
Adam D.
-
Hi, Another way to tell is by " pinging it " ........... Vases , bowls and drinking glasses have a sustained bell like ring.
Regards Patrick
-
Hi
And also the colour.....
it gets very complicated but in simplist form
lower lead more yellow
higher lead more blue
not unlike the difference between standard artificial light and flourescent
cheers
Mike
-
'Pinging' a glass will only tell you about its pinginess - due to shape and thickness of the glass.
-
Being serious this time!
A couple of facts found at random, Lead-oxide glass invented in 1673 by George Ravenscroft,
used the addition of red lead(lead oxide) increased the working life and density of glass.
Main ingredients are 3 parts silica 2 parts red lead and 1 part potash, plus saltpetre, arsenic
and borax.
Lead glass sometimes referred to as flint glass because early example used silicaa derived
from English flints, rather than Venetian pebbles. It has a distinctive Grey tone and is much
heavier than soda glass.
Hope this helps a bit.
Andy :)
-
Flint is also used as a term for soda glass... so never assume.
Soda glass of fine quality will also ring. Monart which is know for its thunk, also throws up the occasional melodious chime. Again, all such hints are part of the arsenal of the collector, none of them are definitive....
-
See also this message from Sept 2004:
http://www.glassmessages.com/index.php/topic,342.0.html
Regarding the Ravenscroft "invention", there are some folk who suggest that the "glass of lead" of those times was "invented" by another person! Also, lead oxide was, apparently, used in glass long before the time of Ravenscroft. It was the amount of lead oxide included that was the crucial factor.
I am fascinated by Mike's comments: "lower lead more yellow; higher lead more blue". I can understand that this may well be true. But, bearing in mind the different colour perceptions of peoples' eyes (or brain), and the fact that women and men generally see colour slighlty differently, how many of us can actually see, or make sense of, the difference in shades of glass with lead oxide? Or is it only in the extremes of "yellow" and "blue" that we could all agree on a difference? Could we be in danger of getting into discussions akin to the "blue tint of Irish glass" as happened in the 1920s :)
-
Lead glass was developed at Nijmegen in Holland by John Odacio Formica (Italian), John Baptiste da Costa and Jean Guillaume Reinier.
Da Costa later 1673 set up a glassworks in England he shared his knowledge with Ravenscroft and two workers went to Scotland and produced lead glass from 1687. Formica wento Ireland where lead glass was made in Dublin in 1675 under Lloyd's patent. Reinier went to Sweden.
See Peter Francis, The Development of Lead Glass, Apollo February 2000, pages 47 to 53
From those earliest times it was known as Flint Glass when it was distinguished from Crystall that did not contain lead. The white lead being derived from Flint.
-
Just to"muddy the waters" a little. Mckearin in his book American Glass states that in 1611 Neri wrote in his treatise on glass: stated that glass of lead was known to few but was the fairest and noblest glass of all others at that day made in the furnace. Neri"s Art of Glass was supposedly translated into English in 1662.
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
Only thorough way to absolutely determine if it is a lead based glass is with a mass spectrometer. Corning labs offer a service that they will run an analysis of any glass you send to them if you're willing to pay the fee.
I think weight can sometimes fool you if it is a barium based glass as it can be very heavy as well.
-
Still trying to find an affordable copy of that but I was aware it mentioned the use of lead. I had not noted the translation date and that certainly ties in well with what Francis says is the 'development' as opposed to the discovery. The speed of take up is interesting too, I am often surprised at the speed which ideas travelled in those days. Presumably as Reinier went to Sweden that country also started producing lead glass at that time?
-
Just to"muddy the waters" a little. Mckearin in his book American Glass states that in 1611 Neri wrote in his treatise on glass: stated that glass of lead was known to few but was the fairest and noblest glass of all others at that day made in the furnace. Neri"s Art of Glass was supposedly translated into English in 1662.
I've just been reading Guttery's From Broad Glass to Cut Crystal, The History of the Stourbridge Glass Industry (1956). He talks about Neri's book (translated, BTW, but Christopher Merret) and a couple paragraphs later there's a quote, "Glass of Lead, beyond doubt the fairest and noblest Glass; if this Glass were as tough as Crystal it would surpass it in beauty...a perticuler sort of Christaline Glasse resembling Rock Christall not formerly exercised or used in this Kingdome" (italics mine). This quotation doesn't have a reference, but strikes me as quite similar to the one Tom talks about, so is it Neri? And what Kingdom? The next sentence in Guttery says, "But glass of lead was not something new; the Lorrainers here had used oxide of lead as a flux in attempts to obtain a more readily fusible mixture when they were forced to cover their pots on the first use of coal as fuel....The technical difficulties which caused Ananias Henzey such troube in Ireland in the sixteen-fifties were probably encountered in attempts to make a successful lead glass." And "W.A. Thorpe, historian of English glass-maiking, asserts very confidently that it was an invention ín the stricter sense of the word, the result of an attempt conceived deliberately and carried out experimentally to provide a sound commercial substitute for rock crystal.'"
...SO, it appears lead was used in a variety of places before Ravenscroft did his thing, but he went down in history for perfecting a high-lead glass.
The Neri bit still confuses me - were they using it in Italy by 1611? It sure would be nice to have that book. Must cost a small fortune.
...I wrote something like this in the Flint Glass thread, but will repeat it here. "The white lead being derived from Flint." Has this been substantiated? It seems unlikely, since flint didn't have much in the way of impurities, it's HARD, and not all that heavy. Would lead have been extracted from it before use, and if not, it seems like it would be hard to control the amount added.
Another quote from Guttery: "At first Ravenscroft had used flints, but the glass which he handed over to English glass-makers when he made no attempt to renew his patent in 1681, was glass of lead." I don't understand why they would be mutually exclusive, doesn't make sense. Flint was just another source of silica. In 1696 John Houghton wrote, "Our glassmen for making the best flint glass use instead of powdered flints a very fine white sand," which could be interpreted as saying that the glassmen used flint still for not-best glass.
-
That might be misleading as the usage of flint seems to have been applied to more than one type of stone. That part of the info is unclear so best ignored.
The record should change so that Ravenscroft was the first patentee in England. Patents were different in those days to what we understand today and were basically gotten via the king/privy council - no doubt in exchange for a fee. If someone came along with more money or more influence the first patent could be annulled and someone else issued with it. Seems to have gone on a lot. So in Scotland the patent went to Sir James Standsfield and Sir Phillip Lloyd in Ireland 1675. Certainly in Scotland the patentee was very close to the king. I have my feelers out for a copy of the Francis's research... so if anyone has a copy. Also if someone knows if there is a picture or text of any of the patents to see if any of the names of the trio appear on it.
Anyway it will be a while before I come back to this as it is just a side issue of my current project.
-
"'W.A. Thorpe, historian of English glass-maiking, asserts very confidently that it was an invention ín the stricter sense of the word, the result of an attempt conceived deliberately and carried out experimentally to provide a sound commercial substitute for rock crystal.'"
Just reread my earlier post. I didn't make it clear that it's Ravenscroft's work he's talking about here. Not that it matters, I just wanted to clarify the quotation.
-
Several pages on hebrew glass history but one also confirms a DaCosta as introducing lead-glass to
Mansell correction Ravenscroft. It refers to ancient lead glass as being a Hebrew invention - outside my sphere of interest.
http://www.hebrewhistory.info/factpapers/fp006-3_glass.htm
Odd how my present research keeps bumping into Lead glass... On they same page also credit Dagnia as introducing soda-glass to Scotland some 50 years after glassmaking started in Scotland - so treat their assertions with respect but caution.
-
We discussed that info on Hebrew glassmaking some time ago (but I can't find it through Search). The general consensus on the Board at that time was that the details seemed to be "tweaked" to suit the author's aims.
However, there was indeed a DaCosta, as mentiond by Hartshorne, Angus-Butterworth, Klein & Lloyd etc. But i think they mentioned him in connection with Ravenscroft, not Mansell. Dagnia (or Dagnias - same person / family??) is also mentioned by those authors.
I have not revisited the texts in detail, so I don't know whether my recollections are fully correct.
-
There was quite a large Dagnia family presence in England, appearing in Scotland during the 1660's.
-
Found a reference discussing some WAY early lead glass, ca. 1550-1307 BC Egypt. Pg 27 in this Google book preview: Julian Henderson's The Science and Archaeology of Materials. http://books.google.com/books?id=p9xJ-VpUuNkC&pg=PA24&source=gbs_toc_r&cad=0_0&sig=ACfU3U16ZtJu-J6Ytel89Memw94beCtrmg#PPA38,M1 (http://books.google.com/books?id=p9xJ-VpUuNkC&pg=PA24&source=gbs_toc_r&cad=0_0&sig=ACfU3U16ZtJu-J6Ytel89Memw94beCtrmg#PPA38,M1)
He also talks about some later uses of lead glass and a variety of other interesting things.
-
It was the use of white lead that was developed by Da Costa and co. It is interesting that this other lead compound was used to cloud glasss.
-
It was the use of white lead that was developed by Da Costa and co. It is interesting that this other lead compound was used to cloud glasss.
I didn't see where it specifically said lead antimonate was used for opacification, though it did say it was used in opaque glasses, but maybe I missed something.
I think it's important to keep in mind that the form of a glass ingredient before it's added and after it has become part of the batch are two different things. The lead compound of the Da Costa white lead and the Egyptian lead antimonate may have been indistinguishable once in the metal.
The question of the development of the use of lead in glass seems to be highly complex. Without the original documentation to refer to I start to wonder about way people have interpreted the data over the years. For instance, was lead used by X for its effects on clarity or color, as a flux, or for some other reason? Was it intentionally added, or was it an impurity in a mineral added for some other constituent?
Is it possible Ravenscroft was working on lead glass before DaCosta or someone else came along and shared his knowledge?
And now I find that something I thought so straightforward, the use of flint as a source of silica, is also being questioned. The development of colorless lead crystal may be one of those topics that I'll leave to the historians.
-
I just found an interesting tidbit in a Google Book (http://books.google.com/books?id=8XdjAAAAIAAJ&pg=RA10-PA8-IA6&dq=english+%22cut+glass%22&lr=&as_brr=3#PRA10-PA8-IA6,M1). It's a quote from a paper read by Harry Powell at Whitefriars. The Google page numbering is a little wacky. The actual page I'm quoting from is 778 in the June 16, 1906 volume, Journal of the Society of the Arts.
The credit of the discovery of lead-potash glass, which is now known as English flint glass, is given to Thomas Tilson, a merchant of London, who, "knowing the glory and beauty of glass of lead, found means to increase the charge of lead." According to the Domestic State Papers of 1663, Tilson applied for and obtained a grant of the sole use and benefit of his invention of making crystal glass.
-
In H. J. Powell's book Glass-Making in England, published 1923, there are a few references to "Tilston (Tilson)" [pages 32, 34, 37, 122].
The first two are commenting on a point that,
The total replacement of carbonate of lime by oxide of lead ... was not, as claimed by Mr. Hartshorne, the result of a sudden invention by Plowden, or Tilston, or Ravenscroft, but of successive tentative experiments to make a more readily fusible glass.
The reference on page 37 covers an entry in a list of "Contemporary Records" and gives:
1663. Warrent for a patent to Thomas Tilston, merchant of London, of sole making of crystal glass and looking glass plates, on surrender of a grant made to Martin Clifford and Th. Powlden the inventers. Patent to Thomas Tilston for fourteen years of the invention of making crystal and other glasses. S. P. Dom.
The page 122 reference is in regard to "Cast Plate-Glass" where comment is made on "the monopolies or patents" granted to Mansell, Buckingham and Tilston.
Harry Powell's book post-dates the 'paper read at Whitefriars' and the S.P. Dom. reference shows that the "grant for sole use" was for future use of a surrendered grant for use of a patent that already existed, not as a grant for an invention by Tilston (Tilson).
-
I noticed later last night as I was cruising Google Books that the paper was the basis for a chapter on cut glass in Powell's book. I didn't read the whole chapter (I doubt it was all available), but saw that it was somewhat different; evidently he gathered more info about Tilston and lead glass in the meantime that I didn't see. I just thought it interesting that there was apparently an English patent for lead glass that predated Ravenscroft's. It's clear that there was a long history of use of lead in glass. Makes me wonder what characteristics Ravenscroft's had that others lacked - why did he get so famous?
-
Patent's at that time had more to do with Royal favour... who you know not what you know.
I would be more interested in the more recent research, just no time to track it down... any Glass Circle members?
-
Makes me wonder what characteristics Ravenscroft's had that others lacked - why did he get so famous?
The list of Contemporary Records listed in Powell's book (see above) includes an entry: 1674. Petition of George Ravenscroft to the King for patent for seven years for his invention of manufacturing a sort of crystalline glass ... ... The Attorney-General ... reported that Ravenscorft's glass was made of ingredients other than those used in other glass-houses in England and the invention may be of considerable use as the glasses made thereby equalise if not excel those imported from Venice ... S.P. Dom.
Also, from The Art of Glass (Nerri / Merrett ) (2006 printing by The Society of Glass Technology), page 3 gives a general insight with: ... and a lead-containing glass suitable for making crystal vessels. This last-named development is usually ascribed to George Ravenscroft and the date of its realization as 1675.
Frank's point about patents in those days is important. They were not quite as we understand them now. And those granted to such as Clifford, Powlden, Tilston, and Ravenscroft were very likely for improvements on a generally known idea. Also, the meaning of "invention" as used in the 17th century was seemingly not as "tight" as many of us would prefer it to be these days!
The fact that Ravenscroft did get a seven year patent and certainly produced glass that successfully rivalled the Venetian products, at least in its stability, would seem to be the reason for his "fame".
But as mentioned before (some time ago) "glass of lead" is now known to have also been made in Holland and perhaps pre-dating Ravenscroft and the other English makers.
-
None of that really answers my question about what characteristics Ravenscroft's had that the previous ones didn't. Stability? Workability? Clarity? Durability? Ravenscroft went down in history for prefecting lead glass somehow, producing a metal that revolutionized the industry. Obviously he was building on a long history of its use in glass, but it seems like if those before him had produced an good formula for blown crystal, it would have spread earlier.
There are a couple articles about Ravenscroft in The Glass Circle 2 (avail. for 10 GBP here (http://www.studiobookshop.co.uk/?page=shop/flypage&product_id=1528906&keyword=glass+circle&searchby=title&offset=0&fs=1&CLSN_1491=12294828311491d1f204eedc477f2126), incidentally) - is that why you asked about members, Frank? Or different reason? I'm not familiar with the organization.
-
Sorry! I read the question as asking about a combination of "general characteristics together with the fame of Ravenscroft". I did not see it is a question of specifics of what the glass had that others did not, as I thought that point had been covered elsewhere and was known by most who had an interest in "glass of lead" ... the issue being that Ravenscroft's "difference" was mainly a progressive increase in red lead which gave rise to a more stable glass than had previously been obtained (as I tried to indicate with my comment, "... successfully rivalled the Venetian products, at least in its stability ...").
Amazingly, I had entirely forgotten about my first reading(s), a few years ago, of the articles about Ravenscroft in "The Glass Circle 2". Perhaps I just interpreted things as being "more technical" than in the general literature but not adding any new info in a general sense. I'll have to take another look at them soon. :)
-
The author is a member of the glass circle and members may have contact detaielos...
See Peter Francis, The Development of Lead Glass, Apollo February 2000, pages 47 to 53
Ravenscroft is regarded as the inventor due to repetition in glass books that did not look deeper, just like Edison is commonly regarded as the inventor of the light bulb.
-
Not sure what the date of this (http://74.125.95.132/search?q=cache:Vw2KEeQxw9gJ:www.cbrain.mistral.co.uk/17gtech4.doc+%22peter+francis%22+ravenscroft&hl=en&ct=clnk&cd=3&gl=us) is, but it's after Francis's paper. Interesting bit about furnace technology playing a role.
Ravenscroft is regarded as the inventor due to repetition in glass books that did not look deeper
I think this is true to some extent. The books oversimplify the picture by using "invented" or "discovered" to describe his work. Still, I'm inclined to think that Ravenscroft did something new that made his glass particularly successful, and the formula the basis of much lead glass after that. But maybe not - perhaps the purity of materials or some technological factor played just as important a role, and he just lucked out.
Kev, I did actually notice what you said about stability a few posts ago. I don't know why I didn't just accept that as the key. Apparently crizzling was a problem in previous glasses. There's also the bit from Powell's book about "successive tentative experiments to make a more readily fusible glass." The paper in the link talks about color issues. So I guess there were a few problems to be worked out.
-
All of what Kristi has surmised in the post immediately above is true to some degree in the complex issue of what Ravenscroft did, and why. I have had another look at the articles in The Glass Cirlce 2 and I am also reviewing again the details that R. J. Charleston gave in his 1984 book English Glass .... I will also re-read various sections of the 2006 edition of The Society of Glass Technology book on the 17th century writings of Neri / Merritt.
For clarification, I will then attempt a brief summary of things, based on those sources, hopefully including relevant points about what was in the glass batches at the time.
-
Hi Being new to the glass message board and having a look at previous posts ,I think the basic answer to this initial post was lost in the discussion of lead glass and its origins ,today the most reliable method of determining the presence of lead in a 17th or 18th century clear glass vessel is to use an ultra violet lamp (blacklight),soda glass will fluoresce yellowish,sometimes very vividly , lead glass will show as bluey grey, the higher the lead content they more bluey/grey it will look ,before UV was available ,and with lead content of early glass being a determining factor of value and origin ,hydrofluoric acid was used , (not recommended today , very dangerous stuff).a small drop was placed on the pontil area and then quickly neutralized and washed off , the mark left by the reaction to the acid by the glass if white indicated soda glass and if Black indicated lead glass,thankfully UV is much easier and less deadly to use .
-
Peter (oldglassman) has made a good point about the basic answer to the original question perhaps getting lost in the detailed discusssion in this thread. The question, of course, was simply; "Can anyone tell me an easy way to tell lead crystal glass from regular glass?"
Peter's observation regarding the presence of lead in 17th & 18th century glasses confirms my own observations with the very small collection of drinking glasses I have and which I believe are 18th century.
However, for lots of items after the 18th century, the uv reactions can vary considerably. Especially for mid 20th century to modern day glass the longwave uv reaction may not show as any shade of blue at all, therefore raising doubts about the presence of lead. But checking the same items under shortwave uv will invariably show a clear blue reaction if lead was present in the mix.
An interesting point about Whitefriars paperweights (but not those made after Caithness bought the rights etc.), and probably, therefore, other Whitefriars glassware from the same time, is that they show a blue uv reaction under both the longwave and shortwave. Most other items I have checked from a similar period show the blue reaction only under the shortwave, with the longwave uv usually giving a weak (or "watery") orange / pink / lavendar colour.
UV tests are very useful, but only in conjunction with other knowledge and uv alone should not be used as a 'simple answer' to the basic question of how to tell lead crystal from ordinary glass, especially across the centuries of glass production.
-
In recent weeks, I have picked up two Kosta Boda Snowball votive (designed by Ann Warff). The other day I was randomly waving my UV light over my glass only to discover one had a nice blue glow and the other nothing. I weighed the glowing one and discovered it weighed 100g more than the other. I checked my lead crystal thoughts by more light waving in the glass cupboard. My conclusion was that the glowing one was older based on the thought that less lead is cheaper.
-
Peter, were you using a shortwave or longwave UV light?
But checking the same items under shortwave uv will invariably show a clear blue reaction if lead was present in the mix.
Kev, is this the case with all lead glass, or just from mid-20th C onwards? Checking with SWUV (if one happens to have one) might be a good indicator.
I don't know about 17th and 18th C glass, but agree that in general there can be great variability in color under LWUV. I have lead glass from about 1890-1925 that shows yellow, lime, light apple green, blue, grey or no response under LWUV, and have heard of pinkish purple examples. Among American cut glass collectors the color is used as a clue to whether a piece (or at least the blank) is American Brilliant Period; those that aren't yellowish green are often thought to be European, though there is debate about this.
-
Hi ,
As far as I am aware , its shortwave UVA, more commonly used for checking bank notes etc,i have no experience in testing post 1800 glass but find it very reliable for 17thc and 18thc , till the batteries run down a little then everything glows yellow,
cheers ,
Peter.
-
Kev, is this the case with all lead glass, or just from mid-20th C onwards? Checking with SWUV (if one happens to have one) might be a good indicator.
The short answer is, "I don't know". But a technical booklet from the 1950s (I can't remember the title right now, but a search through the Board for "UV" might unearth it) had a chapter on UV testing of glass and mentioned that shortwave uv gave a blue reaction for glass with lead. It also said that if the proportion of lead was increased to a [very] high level then the blue reaction disappeared - but I imagine the level for that was higher than would be found in the regular glass we are talking about in this Board.
I suspect that Peter's uv light is actually longwave.
My uv lamp is a "Mineral Lamp" [from the UVP company in California) with both longwave and shortwave bulbs. (There is now also version with a medium wavelength.) I think that the vast majority of single-bulb units, especially battery powered ones, will be longwave ("blacklight") ones.
-
This is an interesting article about fluorescence of different minerals in glass:
http://www.cbrain.mistral.co.uk/home.htm
"The blue fluorescence of lead glass under ‘Hg’ UV lamps is one of the most commonly known responses." However, the paper also suggests how hard it can be to interpret results based on a test by a single light of any sort. For example, iron absorbs light at some spectra, and manganese may emit or absorb light (or neither) depending on its valency and other glass constituents. The fluorescence of lead is more complex than shown here; the paper in the link in the paragraph about lead goes into more depth. One thing that paper suggests is that lead may show different emission peaks depending on how it was added to the batch. It also says that components may show different colors depending on whether they are joined with other atoms or not. The take-home message seems to be that determining the content of glass through emission spectra is in its infancy, and certainly not for amateurs.
One illuminating line from the second paper: "lead, calcium, antimony, chromium, cobalt, boron potash and soda can be detected directly with this system [GABEL: Glass Analysis By Emitted Light] and iron, aluminium, manganese, magnesium and phosphorous can be detected indirectly due to absorption effects." Note that the graphs in the first paper suggest most of these were detected by shortwave UV, and some of them had non-visible emission spectra.
-
Sorry to be late on the scene but this query contains two topics suitable for the glass Olympics, determining lead in glass and the question of Ravenscroft’s discovery?
1. Determining lead.
My experience over some 40 years is that blue fluorescence in the far UV is a virtually infallible way of establishing lead in glass.
I have no evidence that the intensity of colour relates to the amount of lead in the glass. The only sealed Ravenscroft I have been able to test gave a much deeper (Oxford) blue than the more Cambridge shade that is usually seen.
With a near UV lamp (the cheap sort without a filter) lead glass may give a pure light blue, a pinkish blue or even a yellow/green colour with what appear to be 19th century specimens. The yellow/green colour (to my eye) is normally associated with a non-lead glass (usually soda) containing manganese as a decoloriser.
A couple of mid-19th century fairly heavy sugar bowls with a partly matted surface (probably of Manchester origin) ring like lead glass but give a whitish fluorescence in the UV. I do not know why this is.
Soda-type glasses (usually bottles and poor quality glass) often give no fluorescence probably due to the absence of a decoloriser.
Borosilicate glass may give a pink colour but I have not studied this.
All the above relates to essentially colourless glasses. Coloured glasses often quench fluorescence which makes the method impracticable.
2. How much lead?
The simplest way of determining the amount of lead in the glass is density measurement.
With a balance sensitive to 0.1% (or better) of the weight of the object, weigh it in air and then suspended by a fine thread (e.g. button twist) in water. (put something soft in the bottom of the bucket in case the thread breaks!)
Density = wt. in air/wt. in air - wt. in water. Unless ultimate accuracy is required corrections for temperature difference can be ignored but aim for 20 degrees C.
Some 60 or so 18th century English glasses I have measured all had densities of above 2.9 or at least 30% lead in the glass. Non-lead glass has a density below 2.5 and demi-crystal about 2.7 – 2.8 although I have not made many measurements on this. My work on 18th century English glass is published in Paper no. 162 (1973) of The Glass Circle entitled Understanding the Colour of Old Glass. See also E.M. Elvillle (1951) English Table Glass, Pub. Country Life.
Later barium glasses may give high density values but will not fluoresce blue.
I hope this is of some help.
The Ravenscroft question I will deal with separately.
-
This is a favorite topic of mine.
The blue fluorescence under shortwave UV seems to be a pretty good indicator of lead. I now personally believe that it's hard to say much at all about composition under longwave UV for either lead or non-lead, though it's possible that intense yellow green indicates manganese. However, a different color or absence of color doesn't necessarily mean the glass lacks manganese. As the link in my last reply says, "Manganese is one of the most difficult ions to deal with, because it absorbs and emits in the visible region. Previous workers have reported both green and red fluorescence and absorbtion peaks have been reported for the Mn2 ion at 355, 412, 418, 425, 430, 470 & 520 nm depending on the other glass constituents [2],[3],[4]. Fuxi reports Mn2 ion fluorescence at 526 & 606 nm. The Mn2 ion is only present in some glasses if they have been prepared under reducing conditions. The Mn3 ion has not been reported to fluoresce." (Italics mine.)
Soda-type glasses (usually bottles and poor quality glass) often give no fluorescence probably due to the absence of a decoloriser.
Even cheap glass, if it doesn't have a greenish cast, most likely contains some kind of decolorant. There are many besides manganese: cerium, neodymium, cobalt, lead, arsenic, nickel and selenium are some of them, and sometimes they are used in combination. For instance, even lead glass may contain a decolorant besides lead. Choice depends on quantity and type of impurity, and conditions of the batch (e.g. whether it's reducing or oxidizing).
-
krsilber
I agree with your general contentions regarding lead fluorescence and the role of manganese although I have never seen a red fluorescence. The Manganic ion (Mn3) may well not fluoresce as you suggest since lead glasses generally require oxidising conditions. For this reason, arsenic and antimony oxides seem to be the usual decolorising additions to lead glasses, probably from about the middle of the 18th century. Incidentally, I found that Ravenscroft’s perfectly clear uncoloured crystal was made without added decoloriser due to the purity of his materials.
Re your statement: " There are many besides manganese: cerium, neodymium, cobalt, lead, arsenic, nickel and selenium are some of them, and sometimes they are used in combination."
The list of decolorisers you mention need to be considered on a time scale.
Manganese seems to have reigned supreme in both non-lead and lead glasses at least up to the end of the 18th century.
Antimony was certainly used as a decoloriser in antiquity and seems to have emerged, with arsenic, for decolorising lead glass in the 18th century and eventually replaced manganese for this purpose. In the 20th century their use has been kept secret in the UK apparently because of their poisonous nature affecting public opinion.
According to R. Wilkinson The Hallmarks of Antique Glass, 1968, nickel was used from c.1735 although I only ever found one later 18th century glass that might have been decolorised in this way. Cobalt (added in very small amounts on the “blue bag for washing” principle), found some use from the beginning of the 19th century. Both could be used in either type of glass.
Cerium and selenium were discovered by Berzelius in 1803 and 1817 respectively. I would be interested to know if either was much used before the 20th century. Cerium seems to have found its main use in blocking UV radiation in glasses for aircraft and solar cells etc. as well as a glass polish.
Selenium on the other hand has, I understand, been much used in decolorising window glass and bottles of which there are classic American examples. Selenium is limited to non-lead glasses as its pink colour requires reducing conditions in the melt. At least in the early days, a problem with selenium was its low melting point with as much as 90% of the amount added to the batch being lost as toxic selenium vapour before completion of the founding process. I think this problem was eventually overcome by developing more stable selenium salts. Does anyone know the answer?
I suppose that, in theory, anything giving a pink colour could be used to balance the green colour of the ferrous (Fe2) iron. Neodymium would therefore quality, as would praseodymium, but neither was used in glass until 1923 when Moser first used neodymium to colour his non-lead glass pink. Due to its expense I doubt if it has ever found serious use as a decoloriser although perhaps you can tell me otherwise.
Erbium, discovered by Carl Gustaf Mosander in 1843, was until recently just a curiosity. However, it has become a commercially viable colorizer for glass due to its use in mobile phone components bringing down the price. It does give a pretty pink colour; but as a decoloriser . . .?
[/quote]
-
This topic is getting interesting again.
To do a quote, click the quote button on a message to quote it, then type your stuff outside the quote tags. It is advisable to remover superfluous text from inside the quote tags.
To add another quote while editing, just hit the quote button and the quote tags appear, type or past your content there.
Now waiting to read your Ravenscroft :) bit as I never got to see See Peter Francis, The Development of Lead Glass, Apollo February 2000, pages 47 to 53
e.g. of above quote in edit mode
Now waiting to read your Ravenscroft :) bit as I never got to see [quote] See Peter Francis, The Development of Lead Glass, Apollo February 2000, pages 47 to 53[/quote]
-
Very interesting, David!
Do you happen to know when manganese was phased out in Europe? It was used well into the 20th C here. I've seen purple glass that glows red, perhaps from manganese. Kind of odd, since the purple is from Mn3+. I imagine it might be due to the addition of another constituent. Mn is a strong modifier of fluorescence in many minerals. Cadmium + Mn perhaps? Or in this case, the orange glow could be from cadmium alone, rather than Mn, as suggested by the writer: http://reviews.ebay.com/FLUORESCENT-Glowing-MANGANESE-Glass-similar-to-Vaseline_W0QQugidZ10000000000103952
I wonder if sun-purple glass fluoresces less?
Neodymium was used quite extensively in Heisey glass, presumably as a decolorant. Quantities were small. Cost/benefit ratio would depend on how effective each decolorant is.
Hey, I just found an abstract saying that lead reduces the discoloration of glass due to light. http://www3.interscience.wiley.com/journal/119795596/abstract?CRETRY=1&SRETRY=0 I've wondered before Why lead glass doesn’t turn purple. I believe Mn was used in American lead glass (well, I know it was used in some, but don’t know how general it was).
And here’s the beginning of an article that talks about Mn fluorescing red in phosphate glasses. http://www.springerlink.com/content/g34gq6300v5357r8/
-
Thanks to Frank for explaining Quotes I will try it out sometime.
krsilber asks a lot of questions which I will try to answer.
1. Regarding the demise of the use of Mn as a decoloriser I think (without hard evidence) that it continued in use well into the 20th century for non-lead glass. The following 1876 quote from Prof. Fredk. S. Barff, M.A. in British Manufacturing Industries, Ed G. Phillips Bevan F.G.S is interesting.:-
“ ...The material employed was black oxide of manganese. This is still used in certain glass-works, but from its injurious action on the fire-clay pots, arsenious acid or common white arsenic is employed to the same effect.” It then goes on to describe the effect of sunlight on plate glass windows causing them to turn purple. This phenomenon is still visible in many banks of pavement lights around London, particularly when it has been raining and the new clear ones are clearly distinguishable.
Do you remember the scandal some years back caused by “purpling” colorless Lalique car mascots using old hospital X-ray machines. It resulted in a big expensive court case in London.
2. The pictures on the first link do not look to me like Mn fluorescence but typical of cadmium/selenium much used in American red/yellow shaded glass. They may contain Mn as well but I do not think it is the cause of the fluorescence.
3. Sorry, I do not know about sun-purple glass in this respect. If you mean glass purplised by the sun I shall have to go out on a dark night and inspect a few pavements. My guess is not.
I read that neodymium is not a strong coloriser and would be required in some amount to act as a decoloriser. My guess is that this is an advertising ploy. Neodymium gives two strong black bands in the orange red region of the spectrum so you might be able to detect its presence with a hand spectroscope. I have just one piece of Heisey and that is 150 miles away at present!
Re neodymium; when I was in WheatonArts Glass Museum last spring I bought a large glass diamond with a pink colour. The label states that it is Tanznite glass but it shows the neodymium spectrum with my hand spectroscope. The interesting thing is that it turns a clear pale blue by our new light bulbs. In the UK we have just been made to abandon our old tungsten bulbs for new-style, long-life low-energy bulbs said to last 8 years!!! These look like tiny folded fluorescent tubes and have a complex spectrum with strong absorption at the red end. This change in the Tanznite diamond color does not occur with either a near or far UV lamp and, from its weight, I feel sure Tanznite is also a lead glass. This is different again from neodymium in (non-lead) Moser glass which does go from pink to blue under UV light.
Do you have these new-type bulbs in the US or elsewhere in the world?
4. I have looked up the effect of light on glass abstract and it says first “This study was restricted to soda-lime-silica glasses which contain various agents used as decolorizers in glass...” and then goes on to say ... “Glasses which contain antimony discolor less readily than similar arsenic-bearing glasses.” I could not find anything about lead glass. I presume that the stated distinction reflects the different redox properties of antimony and arsenic but don't ask me to explain that.
In a lead glass melt Mn color is very sensitive to oxygen concentration. Phelps Warren in "Irish Glass" cites a mid 18th century reference to color control by adding oxidising or reducing agents. A later reference that I cannot lay my hand on states that (my words) “ In the recent strike (1912) the glass left in the pots for several days turned pink.” This was attributed to the uptake of oxygen as the glass cooled. I have no experience of a direct sunlight effect on lead glass. See also my book "Glassmaking in London" for a more detailed explanaton.
5. The only thing I know about phosphate glasses is that they are slowly soluble inside a cow and therefore useful for the long term administration of drugs – sorry.
-
Hi David,
Fascinating discussion! I have a few pieces of orange Davidson Cloud which fluoresce an impressive orange/yellow under blacklight, due no doubt to the selenium/cadmium cullet used.
On point 3, it's a well known property of neodymium glass that it looks blue under fluorescent light and pink or purple under incandescent or sun light. If you search the board on neodymium or dichroic, you'll find more examples (and some great photographs illustrating the difference.) And in answer to your question, yes, we do have compact fluorescent lights in places other than Britain.
-
David, you have a hand spectroscope?! Wow, I'm envious. That would be fun to play with.
1. Mn was commonly used in the US at least into the 1950s. I hadn't heard about the Lalique case, but sunpurple glass has been an ongoing issue here: some people collect it, so there's a market and a lot of it comes out of the southwest US, where people put it on their roofs or elsewhere outside to intentionally purple it. Many Early American Pattern Glass collectors think it a tragedy and a travesty (understandably, in my opinion).
I have a book of Heisey glass formulas that also has formulas from some other companies in it, and have gleaned much interesting info from that. Heisey used Mn in some of their lead and many lime glass formulas (though the amount of lead would not qualify it as "crystal" as defined in Europe). Neodymium was a common Heisey constituent in later years, found only in their colorless glasses (besides Alexandrite). It is also mentioned as a decolorant in the second link in my last reply, and I've seen it elsewhere. Its effects may have nothing to do with its coloring capacity, just as Mn isn't used as a decolorant because it can make purple.
2. I agree. I guess I wasn't clear enough about that before. So is the glow from selenium or cadmium or both? I thought it was the cadmium, but I suppose if selenium does it too, that might account for the orange glow seen in some colorless glass (especially Bohemian) if selenium was the decolorant. Pure speculation there.
3. We have CFBs, too. They come in regular and a more daylight-like spectrum. Makes me wonder how neodymium glass looks under different types of fluorescent bulbs
4. From that abstract: "Glasses which contain antimony discolor less readily than similar arsenic-bearing glasses, and cerium, lead, and iron oxides in sufficient amounts minimize the discoloration due to light"
I have to think more about electron exchange, color, Mn and Fe in a lead glass melt before saying anything here, or I’ll just make a fool of myself. Chemistry was always my least intuitive science. But I’m interested in this stuff, so it would be worthwhile to look into it more, and I appreciate your comments about it.
-
Glad to hear that there are one or two others besides the UK helping to save the world by using these new bulbs!
Hi Cathy and krsilber, I have a small size Art Deco type orange Davidson vase which also glows as you say. And I have only just realised that it has a circuit of nine panels – how odd!
Anyway, from testing a few other pieces I find that it is the orangey-yellow regions that fluoresce so I guess that cadmium is the culprit.
Glasses with the deep selenium red colour seems to vary under UV. Some have no response at all to either UV while others look as though they have a coating of dust on the surface. But a BIG discovery for me is that a 7-inch Whitefriars bud vase (with original label) does, in fact, have a clear red fluorescence. I had never thought to look at it before.
I suspect that these variations reflect the differing compositions of the batch used for selenium glass that, according to Weyl’s “Coloured glasses”, pub. Society of Glass Technology, can be very complex.
I have had my hand spectroscope for about 30 years. It is like a small telescope with a sliding focus but with a prism and variable slit replacing the objective lens (i.e. the one furthest from the eye). You can buy one on the web for UK£29, probably less in $. There are numerous sites on the web explaining how to make one from a CD although I think that is more difficult than it sounds. Looking out a cheap prism that gives a good spectrum would be a better bet.
I first learned about neodymium from Gary Baldwin’s book on Moser. The point I was trying to make is that while Moser’s neodymium Alexandrit does go from pink to blue under UV light the Tanznite diamond does not although it gives the neodymium spectrum. I have one other neodymium piece, Bohemian or Scandanavian, and that behaves like Tanznite. The common feature appears to be that both contain lead which Moser glass does not. More research is needed on this.
Kristi,
In 1897 Kipling wrote “In makes me feel mysterious to pass that butler’s pantry place.” My wife’s kitchen had the same effect on me!
-
Herewith, in outline, my entirely new explanation of how Ravenscroft discovered English Lead Crystal Glass.
Lead in glass has a long history going back to antiquity. The earliest clear account after the Black Death of 1339 is a mid 16th century recipe book, possibly by Angelo Barovier, described by Moretti & Toninato, 2001, Ricette vetrarie del Rinascimento (translated by me from the Italian). Lead glass at that time was made by founding a mixture of lead oxide with ground flints.The resulting lead silicate was then used as the basis for other lead glasses, particularly false jewels, tesserae and enamels, but was generally too heavy for table ware, and it also had a yellow cast. This remained the basic lead glass on the continent up to and through the 17th century.
Peter Francis , in Apollo, tells us that in 1665 three glassmakers, da Costa, de Regnier and Odacio Formica worked together in Nijmegen (Holland) although there is no positive evidence that Formica was involved as he suggests. Da Costa probably made lead glass there as he emerges as a specialist in false jewels and bijouterie requiring high quality ingredients. There is no evidence that English lead crystal was invented there at that time as Francis suggests. His idea that a special new furnace was essential for the purpose is nonsense.
The three separated in 1668; five years later da Costa ends up in London where he has banker relatives. There is no evidence for an English lead crystal being made in the meantime. Francis tells us that da Costa built a furnace at the Savoy, in London and began making English lead crystal glass.
On the contrary, documentary evidence proves that George Ravenscroft set up the furnace for da Costa in 1673 and Robert Hooke , on a visit with Sir Christopher Wren, tells us that he was not making English lead crystal but “calcedonio”, described by Neri under the English name of “agates” because of its swirling colours.
Calcedonio is made by adding a complex prepared mixture of metal oxides etc. to best Venetian crystal further improved by the addition of the continental-style lead glass, all of which is described in detail in the above mid 16th century recipe book. Crucially, this addition of metal oxides is made not at the preparatory batch level but is stirred into the molten crystal glass to produce the swirling colours.
Working in England, da Costa used powdered flints because Hooke describes them among other materials. However he must have used some alternative ingredients as the Syrian soda, a monopoly in Venice, was not available. Also, following English practice to manage the new coal-fired furnace he would have included saltpetre (potassium nitrate) to protect the melt from smoke and fumes. Ravenscroft would have seen the proofs of the crystal taken to assess the readiness of the melt for the addition of the metallic salts and recognised that here was a glass of such quality as had never been seen before. Calcedonio was forgotten and he took out the well known patent on what was surely the crystal glass itself.
The problem with lead in glass is that under non-oxidising conditions molten metallic lead is formed and attacks and breaks the melting pots (See Neri). Ravenscroft was lucky in that the addition of saltpetre provided the oxidising conditions that prevented this happening. He was unlucky in that although da Costa’s modified lead crystal glass approximated to that of English lead crystal the amount of lead present (9% -15%) was not sufficient to prevent the glass from crizzling without the added metallic salts. It took a further two years, including the trial period, to overcome this problem, revealed in 1676 by the ring of the glass when struck and addition of his seal guarantee.
These events, and the time scale, prove that da Costa did not know in advance how to make English lead crystal glass. Francis and, possibly, Colin Brain (see Glass of the Alchemists, 2007, Corning Museum of Glass), nevertheless support the idea that English lead crystal was “invented” in Nijmegen. One reason for this is that a year after Ravenscroft had been awarded his patent in 1674 Formica applied for, and got, the same patent in Ireland. The most likely explanation is that he was told how to do it by his colleague, da Costa.
These are the facts and bones of the story as I believe them because they fit all the facts without exception. As always seemed unlikely for a merchant, Ravenscroft never undertook experiments to “invent” English lead crystal (stated without evidence for almost a century) at a time (1673) when the crystal glasshouse at Greenwich was said by John Evelyn to be making crystal glass as good if not better than that in Venice. It was a genuine case of “Chance favouring the prepared mind.” The key to the supreme quality of English lead crystal glass was that da Costa was using the very best batch materials available as used by makers of jewels, bijouterie etc.
Ravenscroft did not initially use his invention to make tableware but indulged in the more profitable market of making mirrors. He gave up his patent about the time that his partner in making mirror glasses, John Baker, died. The tableware industry seems to have been taken over by Hawley Bishopp in association with the Glass Sellers.
You will find the full intriguing story in my book; See LINK (http://www.glassmaking-in-london.co.uk)
-
Re Purplised pavement lights:- my reply #52
One of the truly great things about London is that there are people there who collect absolutely everything. One such site is Ghost London which has a section with fine illustrations of purplised pavement lights. With great authority we are even told that the purplisation is caused by ultraviolet light.
To enjoy a quick browse of the site click Purple Pavement Lights (http://www.faded-london.blogspot.com/search/label/lightwells)
From that site you can link to the British Luxfer Prism Syndicate Limited, Founded in 1898 with an address at 16 Hill Street, Finsbury, London, E.C.2. Who apparently made or marketed at least some of these pavement lights.
Other firms are also mentioned including T. Hyatt & Co., 9 Farringdon Road, London, J.A. King & Co, 181 Queen Victoria Street, EC4., and a history of Hayward Bros. that had a factory in Southwark and, later Enfield. Pavement lights may have been a sidekick as it was apparently a foundry that made coal hole covers.
Regarding the origin of pavement lights a strong contender must be Professor Michael Faraday working at the Pellatt and Green factory in Southwark. It would seem that they were first invented to improve the internal lighting of ships. Ackerman's Repository, 1809 vol.1. relating to patent No. 3058 quotes two letters from ship's captains confirming the usefulness of the invention. I have not seen the patent so more info on this would be useful.
-
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.
-
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!
-
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
-
If anyone wants a reference lookup from the Neri book, I have a copy.
-
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
-
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
-
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?
-
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.
-
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!
-
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.
-
Going back to the original question I was pondering recently whether you could identify lead glass by its density in gms./cm3. So looking it up I found soda glass is anything up to 2.4gm./cm3 and lead glass is anything from 3.19gm./cm3 usually up to 4.00gm./cm3 and even 5.9gm./cm3. It's easy enough with a regular solid object to work out its volume in cm3 and divide it by its weight in grams but something like a glass is more difficult. If you can part fill a container with water, mark the level and then submerge the piece in the water and mark the new level. The amount of water displaced gives the object's volume which can then be divided by its weight to give its density. Although it's difficult to do this accurately I tried this with something that was marked as lead crystal and it seemed to work but I'm prepared to be shot down in flames!
-
Hi again :). As you say, measuring the volume of displaced water directly can be a bit difficult to do accurately. I think a better way is to do it entirely by weight.
You suspend the item you are investigating from scales by wire or similar and read the weight when suspended in air. You then lower the item, still suspended from the scales, into water until its entirely submerged and then read the weight again.
If for example it weighs 1000g in air, and 600g in water, then it has displaced 400g of water or 0.4l volume (in fresh water). Obviously you have to be careful of bubbles in the glass and trapped air. I used this method to determine the density of a glass elephant and it worked quite well (although I had to estimate the volume of a large internal cavity).
-
That is another good method, it avoids trying to measure the small differences in water height which might only be a few millimetres.
-
Weight is really the key factor, and the real way ( not simple) is to do specific gravity test.
The normal method of determining specific gravity is to weigh the specimen dry (DW), then to suspend the specimen in water on a string, and to measure the weight pulling on the string (WW) (specimen weight suspended in water). Then you subtract WW from DW, and divide the difference into DW.
Lead is a heavy metal, and lead glasses weight more, by up to 30% for a similar size and
-
Kindly forgive me for my ignorance, but I own a beautiful German flower vase, 24% lead, and I was ordered to throw it away due to the concern of lead poisoning.
Is it safe to have my vase as a decorative object in my living room or should I be concerned?
PS: of course, I will not drink water from the vase and I assume that nobody would do such thing.
(https://i.postimg.cc/vHzFDPn3/IMG-5415.jpg) (https://postimg.cc/ykkrbyvZ)
Amaris by Nachtmann
-
4theloveofmurano, from what I have read, as long as you don't put an acidic drink in it, leave it for a week or more, then drink it, you will be OK :)
-
Anyone knows about this one ?
Thanks
Maky