Topic: frit

[krsilber]

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?

[Sklounion]

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

[krsilber]

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?

[aa]

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
 

[krsilber]

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.

[Frank]

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.

[krsilber]

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.)

[Frank]

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.

[aa]

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.

[krsilber]

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.