Glass Message Board
Glass Identification - Post here for all ID requests => Glass => Topic started by: Glen on June 24, 2005, 09:21:01 PM
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Referring to the thread on "French or Canadian" there is a question revolving around what is "flint glass". I feel this has been discussed in the past. To me, a UK reference to flint glass refers to soda-lime glass.....
Thoughts?
Glen
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This is my understanding of the use of flint glass in the U.S.
Flint glass is glass with some lead content achieved by adding "flint" rock or stone. The lead was not added as elemental lead but as a component of the sand or crushed stone.
Here is a link to the supposed "father of US flint glass"
http://www.findarticles.com/p/articles/mi_m1026/is_2_167/ai_n10017231
Flint Glass was a product of the early to mid-1800s. You will see many EAPG (Early American Pattern Glass) patterns differeniated by flint vs. non-flint. The flint glass examples of the same pattern are generally older and more valuble.
Later in the 1800's glass companies learned how to make a more refined true lead crystal.
What is called flint glass here in the US is a gray tint with various tonal qualities when tapped vs. the dull sound of soda lime glass. (Remember my thunking experiences :wink: )
At least that is my understanding of the term here in the US.
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Glen,
Soda-ash, flint is definitely NOT a PbO glass.
Le Casson
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Hi everyone,
Since I was still awake in the early hours of a fine English morning, I checked a few books (as you do). It seems to me that the question of what is meant by "Flint Glass" is actually a relatively modern thing, possibly arising from a change in regular terminolgy to the now current (?) "Lead glass", or as I often, and perhaps incorrectly, call it, "lead-based glass".
Please forgive my lack of brevity in what follows, but I thought certain quotes would be useful in this context. All bold type is my own emphasis.
From the 1977 book, An Illustrated Dictionary of Glass, by Harold Newman:
Flint. An impure variety of quartz which, after being heated to C.4000, can be easily crumbled and powdered. It was used in England from c.1647 in making FLINT GLASS.
Flint glass. A misnomer for English LEAD GLASS, probably given currency because the evolution of lead glass occurred at a time when calcined or ground flint was substituted for Venetian pebbles as the source of SILICA for making the glass. Later, sand replaced the flint, but the name 'flint glass' has persisted and is still sometimes used to refer to all English lead glass. Flint glass has been classified since 1682 as (1) 'single flint' or 'thin flint', and (2) 'double flint' or 'thick flint'. It has been said that both types were of the same composition, with equal lead content, but that the 'double flint', made to remedy the lightness and fragility of 'single flint', was produced by a double GATHERING of METAL, resulting in a sturdier and more popular (though costlier) glass. A modem name for 'flint glass' is 'lead crystal'.
I can find no distinction in Newman’s book between English and American usage of the word “Flint”. Although there are no source references for the dictionary entries, Newman was (is) a well-respected author on “many aspects of the decorative arts”.
An Introduction for the Dictionary of Glass was written by R. J. Charleston (formerly keeper of the Department of Ceramics and Glass in the Victoria and Albert Museum) whose 1984 book, English Glass and the glass used in England, c.400-1940, covers a lot of research detail that corroborates what Newman wrote.
From pages 114 & 115 of Charleston’s book, these extracts help to put the “Flint / Lead Glass” question into historical context:
25 July 1673 is the date given for the start of Ravenscroft's activities at the Savoy, …. About this time the normal 'English crystal' is replaced in trade descriptions, first (April 1674) by 'fine flint Christalline glasses' and then (from November 1675 onwards) by simply 'flint glasses'.
This is the expression used in the Glass- Sellers' letter to Ravenscroft dated 18 September 1675. Ravenscroft's patent, dated 16 May 1674, bears the marginal annotation 'Flint and Pebble Glass', and we may reasonably detect in this the essential nature of his 'invention' at this date. When later he added lead oxide to his batch, the process began by which 'flint glass' gradually came to be synonymous with lead-glass.
There are many references in older books covering English glass that use the term “Flint glass” or “New Flint glass” or just “Flint” when describing what must surely be what we now call “lead crystal” (or even “Glass of Lead” to use Ravenscroft’s 18th century terminolgy).
Apsley Pellatt, in his 1849 book Curiosities of Glafs Making, stated:
Highly pellucid and transparent Flint Glass requires –
Carbonate of Potash ……………….. 1 cwt.
Red Lead or Litharge ……………… 2 cwt.
Sand washed and burnt ……………. 3 cwt.
Saltpetre …………………………… 14lbs. to 28lbs.
Oxide of Manganese ………………. 4 oz. to 12 oz.
And, in Harry Powel’s, Glass-Making in England, published 1923, he said (page 32):
It may be suggested that the dome-shaped, covered, crucibles were introduced to protect the mirror-plate glass mixture from the reducing action of the fire, and that the loss of heat due to the substitution of covered for open crucibles led first to the use of increased proportions of lead flux to increase the fusibility of the glass mixture and to the gradual development of the glass now known as English flint-glass. … The use of the carbonate or oxide of lead as a glass flux is referred to … in 1611 but the perfected flint-glass, composed of sand, lead and potash, probably only dates form the middle of the eighteenth century.
So, it does look as if "Flint glass" was a regular term used for "Lead glass" from the latter part of the 17th century until at least the early 20th century, but that it was probably just a carry-over from the "non-lead glass" days, perhaps as a convenience for the trade literature of the 1670s and later.
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This is turning into a most useful piece of international research. I am particularly amazed by and grateful for the work that Kevin has put in — it must have taken him hours, particularly if he is, like me, a two-finger typist.
I suspect that the answer will be dependent on context, or time and location, and recall the following:
May I please qualify my remark many times repeated and now described by Bernard as "important". I said that "flint" in Sunderland (i.e. Jobling) meant anything which wasn't Pyrex.
Jobling referred to what other people would call Departments as "factories" even if they were on the same site. Their old, non-Pyrex section was always referred to as the Flint Factory, hence my comment.
Now I only arrived on the scene at Jobling in March 1961, which was a few months after the Flint Factory closed down. I have therefore no first-hand (or, so far as I can remember, second-hand) info as to what they called their individual colours etc. For example I would be very surprised if they called a blue colour "flint". I suppose it MIGHT have been called "blue flint", but I doubt it as there was no blue Pyrex (then) with which to confuse it. I always assumed that they would have called their colourless soda-lime "flint", as we did in Gateshead, but with 20/20 hindsight I now see that I might have been wrong.
How's that for muddying the waters?
Adam
How's that for muddying the waters?
Bernard C. 8)
ps — for readers not familiar with Adam's distinguished career, his reference to Gateshead included his previous employment at Davidson, and even earlier at Sowerby. Adam does not make it clear here whether he was thinking of just Davidson or of both the Gateshead glassworks — I suspect the latter.
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Yes Bernard, Adam is THE guru (and most certainly my guru) when it comes to English pressed glass making.
Kev, thanks so much for your wonderful early morning research. The thing is though, I don't think the glass workers spent a lot of time reading those books, and hence we have the term flint glass meaning very different things depending on the context.
When using the term flint glass in reference to English pressed glass it refers to colourless soda-lime glass. A quick browse through Sowerby's catalogues shows "flint glass" (their term).
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Glen — Adam is my Angel of the North. I have one abiding picture of Adam, in the early sixties, reminiscing with the driver of the old Davidson lorry over his memories of it, on the occasion when it came to Jobling's works to collect all the old "flint" moulds.
Bernard C. 8)
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Bernard - great reply. "Angel of the North" is wonderful. I also refer to him as an Absolute Treasure and most certainly The Guru. :D To be able to hear, first hand, from someone with such a wealth of experience as Adam, is a privilege indeed. I'll sing the praises of another Guru of mine too, Howard Seufer. He is, to me, the US version of Adam. :D He has a wealth of experience at Fenton. I have learnt much from him too.
Glen
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Adam is THE guru
Adam is my Angel of the North. Bernard C. 8)
For recent members of the board, who may not be familiar with the fact that there are a number of Adams on the board from time to time, perhaps I should make it clear that these well deserved plaudits refer to Adam Dodds (Adam D) sometimes described as Adam of York! Or to use the convention that we adopt when referring to each other..."the other Adam"! :D
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But you are wonderful too Adam A :wink:
Glen
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A few recipes for glass may be found here:
http://www.sharelynx.net/web/cyclopedia/glass.html
Judging by the somewhat archaic use of language, these are old recipes.
Regards,
Marcus
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But you are wonderful too Adam A :wink:
Glen
Thanks Glen, but are you sure you're not confusing me with this Adam Aaronson:
http://www.nowplayingmag.com/content/view/1629/47/
We hear a lot about identity theft these days, but this takes the biscuit!
:D
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Illinois Glass co used the term flint in their 1903 catalogue for all clear glass bottles. They often used the term in association - Flint, Green or Amber Glass. Some other colours are also mentioned - Blue, Clear (light green)
Also, c1900 in the US there was the Eastern & Western Flint Bottle Manufacturers (Association)
Cannot find the term in any European catalogues where the distinguishments are more commonly: Crystal, Lead Crystal and Full Lead Crystal.
In Decorative Glass Processes, A L Duthie 1908 New York. Has a chapter describing many types of glass in use throughout US & Europe - not once is the term flint used. However, in the introduction it refers to the fundamental compositions used and here we find flint glass as being made with Sand, Red Lead, Potassium carbonate and Nitre.
Charleston clarifies the use of flint in English Glass. Earliest reference being 1674. Then in 1676 in The Natural History of Oxfordshire "The blackest flints calcined and white crytsalline sand. But then white pebbles from the river Po in Italy which are later suggested to be pyrites. In fact the formulas discussed later state that they do not contain lead but in fact produce BOROSILICATE GLASS. (Needed that for another thread). By 1700 commonly used was litharge (protoxide of lead). Ravenscroft used no lead in his 1674 patent, which was referred to as Flint and Pebble Glass then "When later he added lead oxide to his batch, the process by which 'flint glass'gradually came to be synonymous with lead-crystal."
So in summary flint is used to decribe clear glass and probably for most of history, clear glas with lead content of one form or another.
Can anyone say if red lead = lead oxide?
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Adam said:
Thanks Glen, but are you sure you're not confusing me with this Adam Aaronson:
http://www.nowplayingmag.com/content/view/1629/47/
We hear a lot about identity theft these days, but this takes the biscuit!
LOL! That made me laugh! Adam-Android-Aaronson! :lol: :lol:
Just as an aside, in this technical conversation that's far above my head; Whitefriars call their clear glass items 'Flint'.
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I'm getting embarrassed now! Thank you all, anyway. My wife, by the way hates the (real) Angel of the North.
Now this flint business. My piece which Bernard quoted was in reply to some specific question, now forgotten but it doesn't matter. I may know a thing or two about the practical side of pressing glass but I don't claim any authority on the word "flint". I thought I did, when I first reappeared on the glass scene about the time this Board began. What I said then, based on what I had learned when in the industry, to anyone who would listen, was something like this:-
"There seem to be umpteen definitions of the word 'flint' so far as glass is concerned. In the Stourbridge area it means something which contains no lead. In the optical glass industry it means something which contains a lot of lead. In Gateshead (i.e. Sowerby and Davidson) it means colourless as against blue, green etc. In that case it happened not to contain lead but that is irrelevant because that was all we made. In Sunderland (i.e. Jobling) it means anything which isn't 'Pyrex'".
I explained the last sentence in Bernard's quote. I have just remembered that in the bottle industry some of them talked about "white flint" to mean colourless.
I regarded all that as an amusing irrelevance but when I wrote it, first to Angela and then to others everything went quiet. I later understood why!!
I have first hand knowledge of the Gateshead and Sunderland bits only. The optical glass bit is text book stuff. The rest was more or less hearsay. I did often wonder about the title "Edinburgh and Leith Flint Glass Works" (now Edinburgh Crystal) who are and were, all the time I knew them, distinguished makers of full lead crystal. I assumed at the time that they had started out making non-lead glass - perhaps a good example of bending the facts to suit the theory!
To sum up, I know what "flint" meant locally half a century ago. What it meant then and now, world-wide, I haven't a clue! Anyone quoting me in the future, please include that!
I am so glad that I am only a technical type and not a semanticist or whatever they are called!!
Adam D
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Thanks, Adam, for putting us right in so eloquent a way.
I will, of course, refrain from that analogy forthwith. ... and, I always believed Sem an' Tics was a famous Australian tennis doubles partnership.
Bernard C. 8)
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Can anyone say if red lead = lead oxide?
A quick google proved them to be one and the same.
So since about 1700 flint became the preferred term to differentiate the earlier non lead containing English Crystal which used soda or lime instead of lead. As stated by Hadjamach. It was actually Lead Monoxide or Red Lead.
In the US the name was Red Lead and again it was a component of flint glass at least by bottlers.
Flint is chemically different being Quartz Microcrystalline, greyish black in colour and found in chalk. However it is still an alkali and could in theory have been used as it has been commonly known since antiquity.
Collins English dictionary:
Mentions its use as a component of glass and specifically mentions Flint Glass and White Flint as colourless glass other than plate glass - which certainly supports the notion that those types of glass might not contain flint!
AND
Optical flint is ONE type of optical glass that contains lead oxide.
WIKIPEDIA
With respect to glass, the term "flint" derives from the flint nodules found in the chalk deposits of southeast England that were used as a source of high purity silica by George Ravenscroft, circa 1662, to produce a potash lead glass that was the predecessor to English lead crystal.
with the source quoted as "Kurkjian, Charles R. and Prindle, William R. (1998). Perspectives on the History of Glass Composition. Journal of the American Ceramic Society, 81 (4), 795-813."
This confuses the statements by Hadjamach and lead one to ask both of these sources to qualify their source. However, it does at least show exactly how flint had a use in glassmaking.
TRANSLATIONS OF FLINT (In case anyone can provide info from other countries):
Dutch: vuursteen, iets wat zo hard als vuursteen is
French: silex, éclat de silex, pierre à briquet, pierre à feu, allumage, feu
German: n. - Feuerstein, v. - mit einem Feuerstein ausstatten
Greek: n. πυρόλιθος, τσακμακόπετρα v. βάζω πέτρα στον αναπτήρα
Italian: silice, pietrina, pietra focaia
Portuguese: n. - pedra (f) de isqueiro
Russian: кремень, скряга
Spanish: n. - pedernal, piedra de chispa, piedra de lumbre, piedra de mechero/encendedor, v. tr. - abastecer con piedra de lumbre
Swedish: n. - flinta, stift (i tändare) v. - förse med flinta
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Hello all
Yes, comparing flint vs. soda-lime 'clear' glass is much muddier than the glass! I have always understood that any glass made prior to 1863 in the US was 'flint' (with lead oxide content). 1863 was the date that Wm. Leighton at Hobbs, Brockunier & Co. invented soda-lime as a cheap alternative to the more expensive lead-based formula. The lead-based formula persisted for a while, especially with some of the more traditional glass houses, but they could not compete, price-wise, with the glass companies that made soda-lime formulas. If it has a high-pitched ring when flicked, it is generally considered to have lead in it. Yes, I know, not a good idea to flick glass and some prefer to just rub a finger across the top rim (works fine for goblets, but not spooners!). Some of the elegant glass houses continued with lead in their formulas into later years.
An example:
A few years ago, a chemist's book from Fostoria was sold on eBay. It went to a private buyer for $500. This was the book that was always locked in the safe as 'trade secrets'. In that book, on a page dated 4/2/1928, was the following formula in chemist's handwriting (using chemistry abbreviations from the periodical chart of elements). It just so happened that one of the pages shown in the auction included a formula for uranium/vaseline/canary glass! I got permission from the seller to re-use his photo in my book. I then had Frank Fenton and Jim Measell help me to decipher that page. This was for one batch of metal. The page indicated it was from Pot #8, and it was labeled '305' at the top center of the page.
SAND: 3000 LB.
POTASH: 1825 LB.
LEAD OXIDE: 1630 LB. (labled as red lead)
NITRATE: 240 LB.
TITANIUM COMPOUND 280 LB.
CERIUM COMPOUND 300 LB.
CADMIUM (300 LISTED, THEN CROSSED OUT WITH 'NONE' WRITTEN ABOVE IT - PROBABLY INDICATED THAT IT WAS TRIED BUT LEFT OUT)
URANIUM OXIDE: 100 LB.
comments were listed below the formula: "RESULT: BEST YELLOW YET. STILL HAS SLIGHT GREENISH FLUORESCENCE. NOT SO GOOD WHEN MADE INTO A CUP"
The percentage of uranium oxide as compared to the entire formula is 1,35%, which is about what usually goes into the making of uranium/vaseline/canary glass (1 - 2% of total batch weight). The percentage of lead? 22% for the entire batch.
I found the inclusion of that much lead in the formula to be just as big a surprise as finding the formula in the first place!
Dave
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SUMMATION
Flint was used as a source af silica dioxide and used as an alkali for glassmaking. (It is likely to be shown in more modern recipes as SiO2 or Silicon Dioxide or just Quartz).
It appears to have been largely displaced by Lead Oxide and other alkalis.
The word flint glass was then adopted as a replacement for the term Crystal Glass c1700 but in more recent times glass made with lead has again become commonly referred to as Crystal.
It has been widely used in US and UK to refer to colourless glass and in particular with bottlemaking.
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It is interesting the way that a word with a specific meaning gets adapted, presumably for marketting purposes to become almost meaningless (effectively).
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Checking my reference material, Sowerby, Davidson, Jobling and Bagley all used the term "flint" around the 1930s to '60s to describe standard uncoloured glass, i.e. except special glass such as Jobling's Pyrex and Davidson's equivalent, Silbo. In this context, "flint" is not at all confusing or ambiguous.
Bagley, to a much lesser extent Davidson, and possibly the other two glassworks used the term "white" as an alternative. At first I found this really confusing, as I think of white as a colour, in a similar way to black, blue, green and red. I met the term on Tyneside when I first stood at fairs and markets there some years ago. It was in common use by older dealers and members of the public. I suspect that it may originate from bottlemaking or, perhaps, glasses for the licensed trade.
Bernard C. 8)
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Moved back from Archive for further discussion
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Thanks for that, Anne. The matter has been discussed quite extensively above, but confusion still remains. Flint is 1/ a technical term for early lead glass and 2/ used as a term for clear glass by some glassmakers. Different things to different people - I think that is where the confusion starts. @1 we have sodalime, semicrystal, lead crystal and superior crystal @2 we have the term "clear".
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Yes, thanks, Anne.
First I want to address the main reason I wanted to bring this thread up again. In Frank's summation he says,
"Flint was used as a source af silica dioxide and used as an alkali for glassmaking. (It is likely to be shown in more modern recipes as SiO2 or Silicon Dioxide or just Quartz).
It appears to have been largely displaced by Lead Oxide and other alkalis."
I don't think this is totally correct. Flint was used for silica, correct, but it was replaced by sand. Neither flint nor lead is an alkali, and flint had nothing to do with the use of lead except for the fact that Ravenscroft's first lead glass incidentally used flint as the source of silica.
Now a few questions for Ivo - why would flint be technical term for early lead glass when the earliest true flint glass was lead-free? It doesn't strike me as a technical term at all (though I guess it depends on one's definition of "technical term"!). I agree wholeheartedly it means different things to different people.
Is the "sodalime...superior crystal" a progression of more and more lead added to the batch? What is superior crystal?
Is "clear" the common name for colorless glass in the UK? That's worse than our use of the word "crystal" for it! ;D
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Soda-ash, flint is definitely NOT a PbO glass.
Seeminly not neccesarily:
Continuing alternate points of reference from a French source 1894, analysis by M. Dumas
| | | Flint |
| Cristal | vs. | Glass |
| Silice | 56,00 | | 42,50 |
| Potase | 8,90 | | 11,70 |
| Chaux | 2,60 | | 0,50 |
| Alumine | - | | 1,80 |
| Oxyde de plomb | 32,50 | | 43,50 |
The table includes four types of non-lead glass: Verre à bouteilles, Verre à vitres, Verre à glaces, Verre à gobleterie.
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Since last reading this thread I've come across multiple texts that treat "flint" ambiguously in terms of whether it has lead. Just a couple days ago:
"Under the caption of flint, or crystal glass, many varieties of glass may be properly classed...Such titles as 'lead flint,' 'lime flint,' 'tank flint,' 'German flint,' etc. are applied to glasses graded according to materials used and circumstances contingent to their manufacture."
(Elements of Glass and Glass Making, Benjamin Biser, 1899)
(The same book has a brief discussion of..."Guano seems to be the only substance which will impart a white opacity to glass, and yet be economical in cost and effect on pots.")
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BirdsInit makes white glass, yes I kno-ow ;) we have skylights :spls:, it's the cleaning costs!
booo beat the s**t censor on a quick edit >:D
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Final confirmation of Ivo that it was originally lead glass, sort of poetic to discover it was first developed in Holland:
http://www.glassmessages.com/index.php/topic,10321.msg124233.html#msg124233
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Hmmm, I'd like to read that and see what his references are. Why does everyone else believe that Ravenscroft developed it "working in London in great secrecy" (Short History of Glass, Zerwick)?
The idea that the lead was derived from flint...well, I'm no geologist, but that seems a little fishy. Flint is silica with not a lot of impurities, which is why it was used. And it's HARD, and not that heavy. Was the lead extracted from it beforehand, and if not, how could the amount of lead be controlled?
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Final confirmation of Ivo that it was originally lead glass, sort of poetic to discover it was first developed in Holland:
hey leave me out of this I have nothing to do with it, it is WAY beyond my cutoff dates.
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Flint is 1/ a technical term for early lead glass and 2/ used as a term for clear glass by some glassmakers.
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Flint is 1/ a technical term for early lead glass and 2/ used as a term for clear glass by some glassmakers.
A very fair description. But while no 2 is correct, it is not really in common usage among artists and collectors these days. With the exception of Whitefriars collectors I have only heard one or two people use the term in the last 20 years. :) However its use is still widespread in industry: http://www.britglass.org.uk/search.asp?searchTerm=flint&imageField.x=0&imageField.y=0
You would be unlikely to hear the term in the glass department at Harrods, these days.