Glass Message Board
Glass Identification - Post here for all ID requests => Glass => Topic started by: krsilber on July 09, 2008, 09:43:07 PM
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I think I finally figured out the idea behind frit, and the fact that the ingredients are only partly fused (you glassmakers know this already, I'm sure). Read a bit about it in Cummings's History of Glassforming yesterday. Before gas furnaces it was hard to keep the batch at the right temperatures long enough to "cook" the ingredients to remove impurities and fuse them properly, then make it workable. So it was done in a two-stage process, first sintering the ingredients in a tray to cook off nasty bits and partially fuse the ingredients. Then it was cooled and ground, and when reheated was far enough along in the process that they could melt it to a lower temperature and work it right away. That's my understanding, anyway. In today's use, the fact that frit is only partially fused, rather than simply ground glass, means that when it's used for coloring you aren't reheating actual glass, with all the pitfalls that can entail. More or less right?
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sintering
Using terms such as this..... ::) ::)
Please Kristi, whilst I admire your desire to engage with the subject, do you have any idea, just how daunting you may appear to people?
To throw up terms, without explanation, may make many readers run for the hills, and even seasoned old farts like me, ask...
What is frit, what is its role in the glass-making process, when is it used, how often would it be used and why, what physical properties does it lend to glass, and what exactly is sintering, when applied to items other than press-moulded architectural glass bricks?
regards,
Marcus
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Me, daunting??? I'm kind of flattered!
Sorry, I must unconsciously assume that the only people interested in a thread titled "frit" would be those who knew at least as much as I about glassmaking. But we all know different aspects of it, I suppose, which is why it's so interesting to talk to you all about it.
Kind of embarrassing, really, since I had to try to find a decent definition myself - a good reason not to use the word in the first place! The Wiktionary definition is, "to compact and heat a powder to form a solid mass." I'm not sure whether the ingredients for frit are compacted as they're heated, or what. I thought it was just a way of heating it to a certain point, I didn't know anything about compacting it.
Another definition I came across was on this site (which has a million glassmaking definitions, BTW):
http://www.museumoflondonarchaeology.org.uk/NR/rdonlyres/FCBB7609-4C5A-48A1-9082-F42EBA062F4B/0/post92molglass_glos.pdf
"sintered glass, fritted glass
A porous glass made for filtration and
other purposes by heating graded glass
powder."
And this definition of "frit":
"frit
Calcined or partly fused materials from
which glass is made"
Calcined, as I understand it, is when materials are heated to burn off organic substances. This was sometimes done with sand before adding it to a batch. Sometime you'll see "burnt sand" in glass formulas.
What is frit, what is its role in the glass-making process, when is it used, how often would it be used and why, what physical properties does it lend to glass
As for frit in general (once again, as I understand it), these days it is most often used as a colorant of clear glass, to create layers of differing colors, or for other forms of hot decoration. It's ground, partially-fused glass, and comes in a range of grit sizes. Hot glass can be rolled in it at any point in the production of an item; a blob of glass can have frit applied to add general color, or a shaped piece can have just the surface (or part of it) of it colored. As a silly little illustration, I'm adding a photo of something I know for certain how it was made - the one piece of hot glass I've ever done had a hand in making. It started with a blob of clear, and was rolled in three different colors of frit before being shaped.
Perhaps frit is also added to batches (glass ingredients) when first making them, I don't know. As I mentioned in my first post, apparently frit itself was used to make a batch.
So! That's my brief take on frit, sintering, etc., and I'd be very thankful if anyone out there would correct my inevitable inaccuracies, or expand on what I've said.
Marcus - your reference to sintering architectural glass brick was intriguing. Do you know why they were sintered (and what does it mean in that context)? Was compaction part of the process? And are they porous?
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I am confused by your use of the term "partially fused". I don't doubt that Cummings has a defined explanation for this in certain circumstances, but it does not apply in common parlance to the type of colour used in your flower, so far as I can see. Different people describe the state of those colours, before added to the clear glass, as grains, powders, frits and even enamels, but I have never come across anybody who would describe them as partially fused in this context and to do so could be quite misleading, in my view.
http://www.glassmessages.com/index.php/topic,6269.0.html I think that in this thread frit has been adequately defined, but in the meantime
this link takes you to a page where there is an interesting use of the term, and it just shows how easy it is for a term to be taken out of context!!
http://yespleasenothankyoudropdead.blogspot.com/2005/09/wherein-i-establish-my-devotion-to.html
:)
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There seem to be few different definitions. The Corning one quoted by Frank is more along the lines of what I've read than how you define frit in that thread.
Corning:
"Batch ingredients such as sand and alkali, which have been partially reacted by heating, but not completely melted. After cooling, frit is ground to a powder and melted. Fritting (or sintering) is the process of making frit."
Yours:
"Generally frit is made by immersing hot glass in water. Rapid cooling and thermal shock causes the glass to harden and crumble.There are two ways this can be done.
1. Run molten glass from the furnace into a bucket of water.
2 Heat up broken glass (cullet) to about 500 degrees Celsius and drop into a bucket of water."
Newman's:
"Some of the ingredients used in making glass, such as sand and alkali, pre-heated in a calcar but not completely melted or fused, and when cooled ground into a powder, to be added to the final ingredients that went into the pot (crucible) to be melted into glass."
What Cummings had to say about frit:
"The overriding ingredient for the production of glass from its raw constituents is, of course, heat: to achieve this synthesis directly requires a temperature of 11-1200 C (2012-2192 F), and modern furnaces can work at 1500 C (2732 F). Yet until the 17th century furnaces could rarely reach and hold a temperature of 1000 C. In order to melt glass without the necessary heat to fully synthesise the ingredients an intermediate stage was added. This fritting process continued to be a necessary part of glassmaking until recently in some circumstances. Fritting involved the part melting of the ingredients in shallow pans, which allowed the presentation of a large surface area to the heat source. This burned off potentially contamination residues and created a partial and intermediate form of glass. This was pulverised and formed the basis of the batch for the actual glass melt."
Perhaps the historical definition of frit is different from the definition of the stuff glassmakers use today. But doesn't it sort of, kind of, make sense that the frit used in that glass thing in the photo would be not fully-formed glass, if one wants to avoid the pitfalls of reheating, such as color changes? Just an idea.
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Like all terms that originally passed from mouth to mouth they get re-assigned in the process, often taken from other languages as masters moved to different countries to teach their skills.
It is perhaps backwards to describe processes using industry terminology with all its variability. Communicating processes outside the glass-making world is best done using common language that everyone understands. As whenever any of use our 'learned' terminology, someone always comes up with completely different uses of the term.
So, a 'small' ball of glass gets taken from a pot of molten glass on a length of metal pipe. The cooler metal cooling the glass in contact with the pipe so that is sticks. By blowing down this it inflates like a balloon and by using moulds, bits of wood or other 'tools' the item is shaped. Colours can be added to the outer surface by various methods
1. Rolling the hot ball in crushed coloured glass that has been previously spread out on a metal plate. This colour can be patterned by use of tools. The whole can be covered in clear glass by dipping into the molten glass again or it can be left on the surface. Depending on the amount of reheating an afterwork this material on the surface can be left textured or smooth.
2. etcetera...
Glassmakers use various terminolgy to describe these processes and the terms used vary from location to location, terms such as etcetera
At the next level more details of the glass technologies involved can also be interesting for some of us :), but it is getting to esoteric for most at that stage.
Notice how the topic I started on parison has had little response yet but already the variety is clear.
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Communicating processes outside the glass-making world is best done using common language that everyone understands.
I agree, which is why I made a fuss about "enamel" before.
When I started this thread, my mind was full of what I'd just read in Cummings. I'd always wondered why the definitions I'd seen of frit said it wasn't totally fused; that sort of explained it, and I extrapolated about the rest. I was thinking more about the reason (some) frit was made that way, more than about the definition.
A year ago I would have said frit was ground glass. It's these references that confuse me!
I did run across a patent yesterday for frit that talked about the high concentration of colorants in it; that made me wonder again whether the different chemistry of frit may be a reason it (sometimes) wasn't carried to full melt when it was made.
(Maybe I'll go back to school and become a glass chemist! Ha Ha.)
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I think ther is a mention of how its made in that 1880 report by Colné
... I bet it was I that used enamels that you first picked up on :spls: but then knowing a 'best' way to communicate doesn't mean I always do. As I am immersed in a variety of technical terms all done long I tend to use that language here. Plus, I sort of like those discussions as it helps me to question what I have learned.
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http://www.kugler.co.uk/prod01.htm
http://www.gafferglass.co.uk/
Here are two sites where you can find references to the type of colour used in the making of your flower, which I think was made with what most glassmakers would call grains or grits and not frits.
http://www.gafferglass.co.uk/technical/casting.htm
The link above shows an image entitled frit which is not partially melted glass.
I think you need to be careful of confusing historical terms, which may be correct in a certain context, with common usage.
On the Gaffer glass site, you will find a wealth of technical information, which I am sure you will find fascinating. :)
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I think you need to be careful of confusing historical terms, which may be correct in a certain context, with common usage.
Don't we all!
It would help if someone would tell me, then, what frit is used for nowadays, what its properties are, how it differs from grains and grits, etc. Adam, you say how it was made in that other thread, but not how it's used. It's very difficult to get all this straight when the references say something different from the glassmakers. And didn't Mt Paul talk about rolling glass in frit? Maybe there's a geographic difference in the way the term is used.
I noticed this on the first site:
"Transforming temperature: 480°- 520°C
Annealing point: 500°C"
"Transforming"? What does that mean? Melting? Isn't that considerably lower than a normal batch? And I don't understand how the annealing point could be within that range. Sigh, there are so many things I don't understand, but I do understand people not having the time (or patience!) to explain it all to me. My problem is insatiable curiosity.
I should really get a MODERN book on glassblowing!
I bet it was I that used enamels that you first picked up on
Oh, Frank, I hope you don't feel like I was picking on you!
I make many mistakes, say many wrong things in this forum, it seems. On one hand, that's OK with me because it (often) gives me a chance to learn - with help from you all. Sometimes I wonder, though, whether my credibility is shot as a result, and I just sound ignorant. Oh, well, I'm learning, that's for sure.
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Frit used simply as batch colorant? Better way of adding the materials than separately? Been looking at patents.
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Frit - glass in fine granular form, often made by heating and then dropping glass
into cold water to aid in its break down into fine granules.
Transformation temperature - is actually a narrow temperature range above which
glass behaves like a liquid. It is a result of raising the temperature of the
glass to the point where its tendency to flow is dramatically increased.
(Source: Glossary from "Mixing with the Best" written and edited by Angela Thwaites. 2002 Published on CD-Rom. ISBN 1 874 175 84 5)
Angela is a leading contemporary glass-maker, and the only British artist in glass to have studied with Stanislav Libensky.
Another good source giving contemporary usage of terms is Charles (Charlie) Bray's "Dictionary of Glass: Materials and Techniques" 1995, 2001, ISBN 0812233573 published in the UK by A&C Black, and in the US by University of Pennsylvania Press 1995.
regards,
Marcus
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Thanks, Marcus, for the additional definitions and references. I just bought 3 or 4 glass books; maybe I'll see if my library system has these for now (or the Bray, anyway). Does Thwaites mention what frit is used for?
I just found another definition, this one in Julian Henderson's The Science and Archaeology of Materials. It is on page 38 in one of the Google books "previews" that shows much, but not quite all, the book; there are some other interesting parts that are shown besides this one. 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)
"The basic procedures of glass-making can involve five main steps: (1) the selection and preparation of raw materials; (2) making the glass involving fritting the raw materials; (3) mixing the 'batch' and melting the glass; (4) working the glass to form the glass objects; and (5) annealing the objects....The most enduring ancient glass chemical composition was soda-lime-silica...The alkali (soda), a silica source and a lime-rich raw material are heated together initially to form a 'frit', a semi-fused granular material. True frit is defined as the semi-fused primary raw materials of glass-making (Henderson 1995: 99), in which the formulation of glass has been arrested; it occurs at relatively low temperatures (see Figure 3.12). ...The hot frit may be thrown into cold water where it breaks apart. This procedure may be repeated several times. The main reason for fritting glass raw materials is in order to rmove any impurities, especially gases which are derived from the breakdown of carbonates (releasing carbon dioxide) and sulphates/sulphides (releasing sulphur dioxide or trioxide); another reason is to reduce the number of gas bubbles in the glass-melt."
Of course, I don't offer this definition because it is somehow more correct than others, it's just an alternate one. I don't know what is meant by semi-fused. A patent I just read talks about fritting as simply putting glass in water to break it up (discussing a low-fire glass enamel/glaze). There are enough of both types of definitions that they must both be correct; the more elaborate one seems to be based more on historical procedures.
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Just a couple notes to follow up on the frit business.
A while ago there was discussion of Pyrex on the board, and while I was looking at the Corning site for info about it, I came across some references to fritted glassware. This page is about selecting and using it:
http://www.corning.com/Lifesciences/technical_information/techDocs/frittedglass.asp?region=na&language=en
Apparently it is used in filtration (a use I'd come across before); perhaps that's because it's not totally fused? Still a little con-fused about that.
Then there is this patent:
http://v3.espacenet.com/textdes?DB=EPODOC&IDX=WO2007087125&F=0&QPN=WO2007087125
part of which reads,
"[0044] The batch materials shown in Table 2 were weighed out, mixed thoroughly and placed in a 4 inch platinum crucible in an electric resistance furnace set to a temperature of 2,600<0>F (1,427[deg.]C) and heated for 2 hours. The glass melt was then poured into water at room temperature (referred to as "glass fritting" in the art) to produce a glass frit. The glass frit was dried in an annealing oven set to a temperature of 1,100<0>F (593[deg.]C) for 20 minutes. The glass frit was placed back into a crucible, and the crucible was placed in an oven set to a temperature of 2,600<0>F (1,427[deg.]C) for 2 hours. The glass melt was cast on a metal table"
I wonder why the double melting, same ingredients, same method. Any ideas? (Whew, platinum crucibles! Those must cost a pretty penny!)
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Was just reading bits and pieces of this online book, A Treatise on the Progressive Improvement, and Present State of the Manufacture of Porcelain and Glass (http://www.archive.org/details/treatiseonprogre00portrich) (1832, George Richardson Porter) and came across a passage about fritting that tells nicely what the process did (page 154):
In the first place, it expels all moisture from the materials, the presence of which would hazard the destruction of the glass-pots. Next it drives off either wholly or in great part, the carbonic acid gas from the chalk and alkalies employed, by which means the swelling of ingredients in the pots is either prevented, or moderated within safe limits. This calcination has the further advantage of destroying all carbonaceous matters that may be present in the materials. But the principal object of previous calcination is, that a chemical union may be effected, or at least commenced, between the silex, the alkali, and the metallic oxides. Otherwise, at the heat of the working furnace, the alkali would fuse, and its comparative levity would cause it to take its station at the surface, while the other ingredients would suside towards the bottom. The uncombined alkali would, in this case, after acting upon and injuring the substance of the crucibles, be, in great part, volatilised and lost; and a portion of the sand would remain unvitrified, while the glass actually produced would contain an excessive quantify of silica.
Thes observations do not apply to the preparation of materials for making flint glass, the fusibility of which is much greater than that of other descriptions, owing to the presence of its large proportion of lead.
Perhaps these days the ingredients are refined enough that fritting isn't necessary, and the term has come to mean something else?
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Interesting re-reading this thread and getting it all in one dose, the evolution of the words usage is clearer. That other term Transformation temperature sounds to me like an invention for a specific scientific term (I forget) that was used to describe when a material changes state at a specific temperature. I recall we did experiments in the Physics lab with various materials including water in order to measure the temperature at which the material goes through changes... solid to liquid, liquid to gas and vice versa. But the scientific term has got trapped in those fritting grey cells. :D
Also partly fused can certainly apply to at least much modern art pate-de-verre as well as the sintered glass used for filtering. The end result being a porous material that I have found to be the most effective material for filtering fish tank water. It comes as either coarse granules or short lengths of tubing and is usually an off white colour - the tube makes a highly efficient 'fine' nail-file too.
But defining which is the correct version of the meaning is not possible without the context. To translate terminology to that used in a different context is only going to lead to confusion... so in other words it is better to use the term as it would apply to the period or area of discussion. Dictionaries deal with this by just listing all the different usages and we should follow that establish guideline. Having all the different refereces as above is thus very useful.
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Phase change?
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Thanks Cathy. Just looked that up, and the term I tried to recall was latent temperature. I guess that the term Phase transition/change was not around when I was at school. What I mostly remembered was that the latent temperature of water was fractionally below boiling point and that it a 'strange' state when the water is neither liquid nor gas.
Reading up on it today, it also has strange optical effect... but to take that discussion further would be a cafe topic.
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I think the transformation temp. is that at which molecules change their structure, with a simultaneous change in volume, and heat is either evolved or absorbed. I don't think there's necessarily a phase change though.
What I mostly remembered was that the latent temperature of water was fractionally below boiling point and that it a 'strange' state when the water is neither liquid nor gas.
Reading up on it today, it also has strange optical effect...
That's sounds interesting!
"the sintered glass used for filtering." This is what I was talking about when I mentioned the Corning info about fritted glass.
"Also partly fused can certainly apply to at least much modern art pate-de-verre " Is that before or after it's been "cooked"? (I should know this!)
I agree that the meaning of frit is these days context-dependent. It doesn't seem to be a strictly historical term though, based on the many modern definitions describing frit as partially fused glass ingredients. I still don't know just how the term is applied by glassblowers these days, since Adam said that ground glass is more often called grains and powders than frit (in the UK, anyway). Incidentally, there's something called "pebbles" on the Kugler site (http://www.kugler.co.uk/new_page_1.htm) that looks more like it could be partially fused glass than it does like regular glass, but I don't know if that reflects reality.
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::)
Sorry, I really can't read all that, but my tuppence worth is that I thought it mostly referred to unwanted bits of stuff which contaminate a gather, either from impurities within, or even bits of stuff accidentally picked up from the marver.
It's also a useful, clean swear word, as in ""Fritting prunts!"
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I can't get too technical about this but, when visiting "Escol" (manufacturers of architectural enamel panels in the late 1970's), frit was explained to me as the powder used to impart the colour to the vitreous enanel panels. Escol held recipes for lots of different colours that, in the powdered form, gave you no inkling of what the finished colour would be after firing. Escol were the principal supplier for vitreous enamelled panels used on London Underground at that time and their skills were so good that they could virtually replicate anything in vitreous enamel - illustrations, paintings, you name it. The recipes for achieving particular colours would obviously be achieved through trial and error.
Since vitreous enamel is glass fused to a steel body I suggest that, at that time, frit was the colourant certainly used in the production of vitreous enamel and that the term may also have been applied in the production of decorative glass.
Hope that helps the discussion along.
Ron
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Thanks for the comment, Ron. Interesting that the color of the powder didn't reflect the final coloring. That might suggest that the metal oxides used weren't yet a part of the glass powder component (or it wasn't fully fused??).