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Marc Leva 04-02-2005 10:51 AM

Re: (blah blah blah continues….)

Originally posted by Lani McGregor
I originally asked this question (started in the prior post) because I honestly don’t know for sure whether Glass Fusing Book One is the original source of this bad science. But from what I’m reading on this board, this (early 1980s in the fusing sector) is where the measured COE as a synonym for compatibility first showed up in studio glass.

Glassforming;glassmaking for the craftsman by Frederic and Lilli Schuler ©1970 pp.97-98
"When glasses are mixed, it is important that they have the same coefficients of expansion, so that stress is not set up at the interfaces between the different glasses after cooling."

Tom Littleton 04-02-2005 11:08 AM

I asked HKL if he ever talked about COE in his seminar. He said that he did not. He indicated he did know about caculating COE even before he got into glass but seemed to have considered it superfluous. He said he used the empirical (trial and error) approach and knew about making things "fit" from his years as a potter before he got into glass.

An interesting aside is that he did say that he knew both Scholes and Green and that Green had lived in Corning and had worked for his father (J T Littleton) at Corning. Also some years ago HKL told me that he used to play poker with Labino in Toledo when he taught at the Toledo Museum. That would have been in 1950 and 1951 before he moved to Wisc.

I asked when he first knew about Kugler and he said he visited Herr Kugler in Olenburg sp? before he moved to Kaubeuren-Neugablonz but couldn't say what year.

The Wooley data is from his book "Glass Technology for the Studio". I believe that the tests were done in the Corning Labs.

Just to confuse the issues
From Robert Stephen in 1996 come these results (done at Corning Experimental Labratories I believe). These tests were done to the ASTM C336 standard. Annealing Point-499 degrees C (930 degrees F) and Strain Point-461 degrees C (861 degrees F)

We originally got an 890 annealing point from Nick Labino and that is what we put in our literature.

Anybody who asks me about annealing point and annealing gets a whole "song and dance". I tell about how inaccurate thermocouples can be. I then tell them to calibate their annealers using the sag test and mention Henry's book (so that I can tell him how I'm promoting him and stay on his good side). I also mention the need for some kind of polariscope to check for strain.

Some of you may remember the old Wiesenthal sp?. It had the expansions printed on the bars. The first stuff that was availible was just under a 100 COE.

Steven O'Day 04-02-2005 11:47 AM

Peter - I agree, expansion was widley taught in the ceramics programs at the time.

Lani - My recolection is this: I worked at Bendheim for a short while and went back to studio work. Therese was at CR Loo and I distinctly remember having conversations with her about them testing some clear glasses and how expensive it was and being surprised how far off the tested numbers were from the calculated. I don't have the catalogs either, but the glasses probably were Gabbert/Louise, SP and maybe East Bay (though this may have come latter). I think there was a Schott in there too.

I don't remember any specific reference in Scholes and am not inclined to go looking having had a hard enough time with it the first time.

But what exactly was that "same thing"?
When the question of fit came up in a workshop the only thing I remember being discussed was expansion. There always was talk about how even if the expansion was the same, sometimes the glasses would still not fit. You are correct in stateing that glassblowers should have known about viscosity being a factor and of course we did, having to deal with it in every piece that has two different types of glass. But no one that I know of knew how to measure it.

My working strategy was to ask around about color fit first. Pull a cane test, if it was way off return the color. Fuse some chips to a rondel and look at through the polariscope, if way off return the color. Maybe make a paperweight with the color and a lot of crystal and look at that. I would sometimes do the ring test, mainly if I wanted to show off. I think this was more testing than a lot of studios did, but not as much as some.

fusing Bullseye (that famous "90" glass) to Desag Artista and because most of it isn't cracking wildly, dealers are listing Desag as a "90" glass - contrary to what the manufacture lists as their measured COE
Copy writers, the bane of truth everywhere.

I doubt that you will ever get a definitive answer to your question.

Lani McGregor 04-02-2005 12:38 PM


Originally posted by Tom Littleton
From Robert Stephen in 1996 come these results (done at Corning Experimental Labratories I believe). These tests were done to the ASTM C336 standard. Annealing Point-499 degrees C (930 degrees F) and Strain Point-461 degrees C (861 degrees F)
Tom, thanks for this! Great info
Why were these tests done?

Was a COE measured at this time? If not, why not?

Did Robert's tests pre-date Woolley's?

Lani McGregor 04-02-2005 12:45 PM

Re: Dan & Boyce are innocent! Arrest this couple...

Originally posted by Marc Leva
Glassforming;glassmaking for the craftsman by Frederic and Lilli Schuler ©1970 pp.97-98
"When glasses are mixed, it is important that they have the same coefficients of expansion, so that stress is not set up at the interfaces between the different glasses after cooling."

Well, thank GOD!

But who were the Schulers? Flameworkers?

Again, I think this is "popular" science (with its typical half-truth).

Does the book mention what glasses they were mixing?

Lani McGregor 04-02-2005 12:56 PM


Originally posted by Steven O'Day
You are correct in stateing that glassblowers should have known about viscosity being a factor and of course we did, having to deal with it in every piece that has two different types of glass. But no one that I know of knew how to measure it.
But you DID know, you just didn't know you knew:


... Pull a cane test... Fuse some chips to a rondel and look at through the polariscope.... Maybe make a paperweight with the color and a lot of crystal and look at that. the ring test,
These are all tests that measure the combined results of COE & viscosity (you can't separate the two). None of these tests measure COE. You DID know how to measure viscosity.


Copy writers, the bane of truth everywhere.


I doubt that you will ever get a definitive answer to your question.
I don't need a definitive answer. I'm just looking for extenuating circumstances to get my husband's sentence reduced for aiding and abetting Bad Glass Science.

Marc Leva 04-02-2005 01:31 PM

It started on Mt. Palomar
Here's my convoluted theory.

Dr. Schuler (Ph.D U Wisconsin'49) was senior research associate of the Fundamental Chemistry Group, Corning Glass Works from '53-'56 and administrator of the Scientific Research Program, Corning Museum of Glass from '56-'58. While with the museum he met F. Carder and had a chance to work on casting in his workshop. His wife also worked at Corning in a scientific capacity.(from the dust cover)
He did other types of art (drawing, clay, etc.) for several years and the started doing flamework in '67 which led to him writing a book on flameworking. Then he started doing casting again. Also in '67 at Corning 2 large cast disc were made. 1 - 157 inches dia. X 25 inches thick, 1 - 144 inches dia. X 20 inches thick. The first weighed 18 tons; the second , about 12 3/4 tons. They made them from smaller pieces of glassy (not crystalline) silica that were preshaped, arranged in the mold and fused together. Glassy silica was used, among other qualities, for its low expansion. Its expansion is 4 and I think the Palomar was boro at about 30.
The book has many qualifiers when it talks about COE. Its mostly in the context of enameling on glass or casting. It also has charts and grafts and comparisons of all kinds of different things until it starts to take on a bibilical effect. If you take a passage from the front and pair it with an unrelated graph in the appendicies and then confirm it with a paragraph from the back on a different technique, well hell, things start to make a weird kind of sense. Different qualities take on strange proportions. And I think for Schuler, at least, he was impressed with the whole glassy silica lenses low COE and its in his book alot.
Living down here 240 miles south of bum****, I didn't get this book until it was recommended to me by James Broadwell at Ruthglass. That was in '81. There just wasn't any information for casters and this was an incredibly helpful book. I don't know when David Ruth started making glass but the book was there in '70 and Schuler was living in Santa Barbara, Ca.
Just a guess.

Lani McGregor 04-02-2005 02:31 PM

Marc, Oh good, Mr & Mrs Schuler weren’t bongmakers by trade. Whew!

But the earlier statement "When glasses are mixed, it is important that they have the same coefficients of expansion, so that stress is not set up at the interfaces between the different glasses after cooling" is still without enough qualifiers to be applicable to all studio glass situations.

Primary missing info here is:

1. What glass were the Schuler’s working? Were they mixing glasses with the same annealing points (i.e., the same viscosity)? If so, the statement is undeniably true.

2. Does Schuler mention which COE he’s talking about? 0-300C? Or a COE for instance in the 500-530C range?

So much of the problem today, as has come up earlier in this thread, is with the mixing of color where the viscosities – which are indicated by the AP - are often so different. Finding any reference in the technical literature to compatibility issues in mixing colored glasses of different base compositions is close to impossible.

The other problem with part of this discussion is a semantic one: the mismatch of glasses is commonly referred to as an “expansion” problem, but the term “expansion” used this way refers to the strain between the glass, NOT to the LEC of either or both glasses. This expansion difference (or strain) is not solely the result of LEC differences.


PS. Marc, I don't mean for you to have to spend your Saturday copying passages out of this (great reference, thanks!) book. I'll go track it down and add it to our library....

Marc Leva 04-02-2005 03:40 PM

The book is not really technical. I does have charts and graph and tables but they don't all have the same information. It has a graph of viscousity coefficient verses temps for "several" glasses against "ordinary material (300C-1000-1200C), next page the same for Corning Code 8391, PPG Pennvernon and LOF Colburn glasses. Then a table with COE of fused silica, boro and soda-lime glass. Then a graph showing a generalized expansion of glass colors with a substrate glass that ranges from 0C to 510C. Individually they don't mean much. But if you mix and match the info anything is possible. I didn't mean to deflect the origins towards Schuler or David. I'm just saying that the book was on the W coast and so was Schuler. If your a young guy wanting to make sheet glass, like several people were attempting at the time, wouldn't you ask around? If some guy who'd worked at Corning was available wouldn't somebody talk to him?


But the earlier statement "When glasses are mixed, it is important that they have the same coefficients of expansion, so that stress is not set up at the interfaces between the different glasses after cooling" is still without enough qualifiers to be applicable to all studio glass situations.
Thats the only sentence in the whole book that doesn't have qualifiers within the sentence. And it actually refers to striae in a clear glass body.

I should be working on my taxes. I'm just working down my procrastination list. I had a very small triumph in the studio yesterday and I'm not set up for any failures till tomorrow so, I'm staying out of there to bask briefly. Its this or taxes respond faster, please!

04-03-2005 07:04 AM

OMG!! Total Flasback!

Waay back I did Stained Glass and the Ruth Glass -End of Day sheet glass was Totally AWESOME..amazing colors the glass cut like butter.. !!

I went into my secret stash and found I still had several End of Day Ruth Glass Sheets !! yippee!! I had forgotten about them !!

In 1980 Tony Parker came up to Alaska and did a fusing glass workshop.. that was my first exposure to fusing and the first time I heard of COE..
followed by Doug Hansen, (fuser and caster ! ) Ruth Brockman Richard LaLonde,Liz Mapelli , Boyce , (your little buddie..just loved when he pitched his dinner fork at Cathy during dinner... thank G-d his aim sucked ! ) they were all big into teaching compatibality..expansion and COE ..and "TOUTING" B/E Tested Compatible Glass!

my first exposure to issues of COE and "fit" was with fusing and Bulleseye. Glass.. Looks like yur company may be guilty after all Lani.. of "spreading the word" in the 80's Fusng Book# I was a "bible" / manual / guide to fusing.. original book had graphs and charts on testing.. and COE.. !! Followed by Gil Reynolds book..

Therez at CR Loo did do COE charts.. ( I hate to clean !!) and then they were picked up by OCR in their catalog..

Bad Science or not.. seems that Bulleseye Tested Compatible put the concept of COE 'out there' in a huge way.. and it is still out there.. sorta like a Jeannie outta the bottle...too late to put the cork in it.. and yu want to put the cork in the bottle why??

mmmm.. seems that COMPRESSION and TENSION HAVE NOT been mentioned in this discussion, and they are very important to the way a 'blower" uses color bars and base clear!


someone check my memory. on this...

was not the "standard" base glass , for blowers, back in the 80"s, and early 90's Louie cullett??
I seem to remember 'everyone 'used Louie until the day that Louie "changed " their formula and forgot to tell their customers!! and all hell broke loose.. glassblowers lost huge amounts of work as it sat in the just blew/flew apart!

was this not the time when Spruce Pine Batch took hold among glassblowers in a large way?

Lani McGregor 04-03-2005 01:08 PM

Dammit! the snake oil bottle is leaking...

Originally posted by CynthiaEngland

… they were all big into teaching compatibality..expansion and COE ..and "TOUTING" B/E Tested Compatible Glass! … my first exposure to issues of COE and "fit" was with fusing and Bulleseye...

I’d agree. “Touting B/E”. Boyce was a Salesman and COE = compatibility certainly made fusing easier to grasp for the hobby market. And “easy” is more saleable. But that doesn’t make it correct. But Boyce left Bullseye 20 years ago. And in spite of all the qualifiers that Dan tried to put into GFB1, the demon-child of COE & Compatibility lives on.


Looks like yur company may be guilty after all Lani.. of "spreading the word" in the 80's Fusng Book# I was a "bible" / manual / guide to fusing.. original book had graphs and charts on testing.. and COE.. !!
Yes, but read the qualifiers in that book about how glasses with the same COE may not fit and how COE is only a “starting point”. Seems like our entire market just zipped over that. How come people weren’t screaming “why not?” IMO, because it’s easier to SELL if it’s SIMPLE. Screw ACCURATE.


Therez at CR Loo did do COE charts… and then they were picked up by OCR in their catalog..
We still don’t seem to know HOW Therese came up with her numbers. But you just gave me another piece of the puzzle. I’d wondered where OCR got the numbers on their charts. They are interesting:

How come there’s no “Measured COE” for Gaffer on that chart?

Why, instead, is there this statement from Croucher:

“Gaffer Color range will show very little retardation and thus very little measurable strain, when fused to a typical soda lime glass that measures at 96 x 10-7 (20-300C) and has an annealing range between 450-520C (840-970F).” -John Croucher

Because Croucher knows full well that a COE without the qualifier of viscosity can be very misleading information. So he suggests the viscosities (annealing points) AND the additional qualifier “typical soda-lime glass” needed for the COE to work.

And the other data, according to you, was just lifted off the C & R Loo charts. Well, that information (“90 COE”) is wrong for Bullseye. Why should anyone think it’s right for the other color makers?


Bad Science or not.. seems that Bulleseye Tested Compatible put the concept of COE 'out there' in a huge way.. and it is still out there.. sorta like a Jeannie outta the bottle...too late to put the cork in it.. and yu want to put the cork in the bottle why??
We just want to let the “Jeannie” of viscosity OUT of the bottle and clear up some of the rampant – and increasingly problematic – half-truths that the Salesmen (yes, Boyce was one of the pioneers) have brought into studio glass. This industry – I guess it’s a sign of growth – has gotten rampant with Salesmen. And the users seem perfectly content to accept marketing as technical information.

I may be hyper-sensitive on this issue – having been bashed for years by David W. who believes that every piece of technical data that comes out of Bullseye is a sinister PLOT to control the market – but why would you even ask why we want to “put the cork in the bottle”?

OK, truth is , we’re drilling for Viscosity in the Arctic National Wildlife Refuge and if we can convince the studio glass community that it’s got value, VISCO-BULL, LLC. is gonna make us richer than King Fahd.

Shit, Cynthia, I knew it would take a blond to figure it out.

Pete VanderLaan 04-03-2005 01:45 PM

jeez, I just had to get away from this and do something fun, SO I just did an alchohol intervention, flying from Santa Fe to Denver to LA to Denver and back to Santa Fe in 24 hours. On the way back, I sat next to a valley girl who watched MTV , giggled incessantly and who keep applying a lip gloss that smelled exactly like the little cake in a men's urinal.

Anyway, I did some testing for CR LOO but it wasn't that far back.. I think I did it in about 1996 or whenever Croucher was bringing Gaffer into the market. I do recall asking for formulations on various glasses and getting most of them with the exception of GLASMA who would only supply a stupid pie chart that was useless. My recollection of Theresa's efforts was that she simply collated the responses from various manufacturers. and believed them. ( I mean crap, she believed me,)

I don't have the article right in front of me but my distinct recollection of the 1.5 ten thousandths difference was mentioned specifically in Manner's article.

If you really think about it Paul could take the blame for all of this and get Dan off of his invisible hook, especially since none of us know where Paul is: His article only talked about expansion and never about viscosity as being an issue.

When I say "mention viscosity and eyes glaze over", They do. I wish they didn't but they do. Glassblowers by and large really take no responsibility at all for their materials.They want to be told "It fits" which is essentially what Bullseye tells them. When I mention that the expansion of a certain clear glass being imported wanders all of the time when I test it, I suspect that the viscosity does too, I have no motivation to check it. Even so, glassblowers buy the stuff by the ton and scoff at problems until they inexplicably have them and then it's almost always someone elses fault.. With many of the clear cullets, they are not designed for handblowing but are designed to go thru gob feeders and never have to be mated to another glass type. They were never intended to be used in small shops or matched to "Isotoner" color rods. People want to be lulled into complacency and they really really want to believe that weight gain isn't their fault and that you can lose weight sitting on the couch eating Pizza if you just take Cortisol. Eyes glaze over because being responsible involves real work.

I actually think people would be happier with Heidi Broderbund's 15 percent rule that the beadmakers used to hold up as the first of the ten commandments. Grrr....

The part of the puzzle that never gets answered for me is why German color rods, with their 45 percent lead and their clearly wildly different viscosities will fit ( meaning they don't actually explode) the bulk of clear glasses marketed today in blownware. The expansions aren't far off but the viscosities are and you can visibly see it in the bleeding that occurs when any german stick is applied to the surface of ant clear glass. It's like an ink stain on a white carpet. It fails when you saw it so guess what? People don't saw it and say it fits. Would you stand under a chandelier made with Spruce pine and Kugler's bright yellow opaque? I wouldn't. ( and I know it's not a lead rod.)

04-03-2005 05:48 PM

Being only interested in confusion rather than in answering Lani's question, I want to add a question to the viscosity discussion. Why does anyone think that measuring viscosity in the 17 to 300C range tells the story of what happens over the entire annealing range? Do all glasses remain linear above that temp up to their annealing point? And isn't a 40 or 50 degree difference in annealing points (or strain points) sufficient to create a fairly large difference in the total contraction that each glass experiences? I favor the behavioral tests over the theoretical because all of the factors that we can or can't measure are included. The ball test is one that no one has mentioned. Take your color and gather a clear layer over it. Shape and anneal. Observe cracking if any. Look at through a polariscope. Most problems will show up at this point. If you want lots more evidence or reassurance do the following. Saw it in half. Observe. Saw a slice. Observe. Look at through a polariscope again. Polish one face (this micro-heating can set off latent strain). If there are problems, compare to a pull test tt determine what the problem is. I think Lani hit one thing right on the head. There is skill in doing a good pull test and they should be repeatable. And there are limits to what they mean, but a dilitometer test of expansion over the lower and of the cooling range doesn't tell the whole story either.

Pete VanderLaan 04-03-2005 06:36 PM

well, the curiosity I run into, and I agree that neither a pull test or a dilatometer test tell the definitive story BUT when I do a ring test and I get a slight gap, it tells me that the inner glass needs a higher expansion. If in 100 lbs of the inner glass, I add about 100 grams of sodium, or another of the alkaline fluxes, the gap usually closes. That is true in either opaques or in transparants. What it doesn't say as a test again applies to viscosity and it is grossly obvious that the viscosity of a soda lime clear is way way higher than it is in a fluorine opal. My opals actually melt at about 1975-2000F which really tells the viscosity difference in a heartbeat. Now I can get these two totally dissimilar glasses to do great in a ring test, to give me a consistent readout in a dilatometer, give me terrible pull tests have totally different softening point but saw like a dream and grind like a dream, never break in blownware, but check if there is too much of the opaque in relation to the transparant soda lime present. That is as in 2 inches thick or so. At one point I was making some weights that were about four inches across. I would take two big gathers of the fluorine cased in clear and they would crack. If I used a gather of clear, then the fluorine and then the clear, they were perfect and never gave any trouble. If I blew those glasses together, they never gavwe me any trouble. I could grind and I could saw and they never gave me any trouble. I varied annealing schedules and it never affected a thing. I don't know what the deal was.

Now I know that the fluorine crystals are growing, collapsing and regrowing as the glass ages but it's viscosity doesn't seem empirically to be changing much. I suppose I could continually check it each day for differences, I just never have. I am simply observing that as the density of the opacity goes away, the viscosity doesn't seem to go along with the density loss.. When I make color rod or frit, I capture the density of it usually about ten hours after the melt and I have not had occasion to watch its characteristics deteriorate in a measurable way/ ( nor do I care to)

Chuck Savoie used to say to me, and it really applied to cad sel opaques particularly when we were screwing with some of the old Thuringen formulas,, "Sometimes it's so far out, it's in." The information is so conflicting.

Cold comfort.

John Croucher 04-03-2005 09:07 PM

When Gaffer was started in the early 90's the biggest headache was what expansion/viscosity standard was out there for glassblowers. Whereas the fused glass manufacturers could totally control compatibility in-house, color bar makers had to somehow fit with a myriad of clear batches around the world. In Australasia alone we were faced with 20 odd recipes with widely varying LEC's and viscosities. The Germans were no help, since their pallet was all over the map.

The other problem was what was the best test to check compatibility in-house. Industry standard dilatometers offered no better than +/- 1-2% accuracy and cost upwards of $20,000 and the info was useless unless the respective strain or set points were concerned.

I have to thank Frank Woolley at Corning for pointing us in the right direction, a direction that the fusing manufacturers had been pursuing for years. Measure the mismatch with polarised light and a trident seal. The fusers use flat glass -cane makes more sense for hot glass workers. The trident seal takes care of differing viscosities up to the respective strain points of the glasses, as well as differing Youngs modulii, emissivities, surface tensions and of course LEC's. The strain, whether in tension or compression can be read very accurately with a polarimeter. After a while the retardation can be interpreted chemically when adjusting a batch. We can look at the results and know something needs adjusting up or down by what we call LEC on our spreadsheets.

That still left the question of what to be compatible with. Looking at what was potentially our biggest market globally, there was an obvious Titanic out there -Spruce Pine 87 batch. Even though we felt it's contraction was a little high compared to most of the German glasses (we didn't want to be in our own universe) we adopted it as our standard. We then created Gaffer Batch which was compatible with SP87. That is now our standard.

We are still totally at the mercy though of peoples melting practice, length of time their clear is in a pot or tank, whether the clear batch has been mixed correctly etc. In Europe we are up against widespread use of Glasma batches which are far too high. The same goes for Japan. Vast numbers of glassblowers think a thread test tells them everything when it doesn't, unless the two glasses are very close re LEC and viscosity. It's time we caught up with the fusing scene, which had all this stuff figured out 20 odd years ago. I agree with Lani -measured COE's have become a lazy way of descibing a glasses compatibility. We are guilty of it ourselves. Unfortunately there isn't a quick way of resolving this problem, because there isn't a standard glass. If there was, then one could compare all the studio recipes to it by quoting +/- retardation variances as nanometres/centimeter

Jordan Kube 04-03-2005 10:06 PM

So your weights were breaking because of a viscosity mismatch. While the outside set up the inside was still hot. This is how things cool down. By the time your flourine was ready to set up the clear wasn't going to give at all creating tension within the piece. Does your flourine set realy fast once it reaches a certian temperature? My thought is that the glass may be good at creating stress within itself if it's thick enough and then adding the clear over it just makes it worse. Maybe you could have slow cooled it by flashing the thing in the glory hole for ten minutes. Who's got time for that? The clear flourine clear arangement probably helps sandwich that tension a bit. I think the blown ware is structurally stronger at distributing the stress evenly throughout the piece provided that it's round. There isn't such a difference in the rate of cooling from the outside in with blown ware either. I think you gave the best example about what this is all about.

Jordan Kube 04-03-2005 10:13 PM

Would the same shape and size weight made entirely of the flourine glass hold up to the saw?

Pete VanderLaan 04-03-2005 11:25 PM

the term "set-up" is not a good one to use really. The dfferences here are ones of viscosity and annealing point which go hand in glove. I was simply trying to demonstrate how one can have most of their ducks in a row in most instances but there will still be exceptions that will give you trouble..

John knows that while I really respect the trident seal that I think it is so sensitive that the sample breaks very easily unless it is damn close in the first place. A lot of what I am looking for is methodology that lets a studio glassmaker analyze their process in a variety of approachable ways. The polarimeters that John uses run a couple grand and while I don't deny the accuracy of the system, I don't think many private studios are going to be willing to make that investment It is where I think the ring test is a very good indicator for not a lot of cash. I think the trident makes sense for major manuafacturers like John but I don't think it's necessary for people who want to make their own colors in house. It is really still the case that if a piece survives the diamond saw while making the ring, the piece is effectively compatible. The ring gives the very fine tuning indicators in the same sense that John's trident seal does the same, or at least that's my opinion.

As to the fusers, I think that bullseye effectively guarantees compatibility within a closed system and that makes perfect sense. Spectrum apparantly does the same thing but by calling their product system 96, the implication is there that any glass hawked as a 96 L.E.C. is going to fit right in. It won't. The fact remains though that the bulk of glasses being produced today have to acknowledge what John calls the Titannic in the room which is SP87 which I think still has a clear majority of market share in commercial batches in this country. Even if it doesn't, the other manufacturers are still shooting at 96 and their annealing points and viscosities are really not far away from Spruce Pine. If they were, we would really be hearing about compatibility issues all of the time and we aren't. The cullets are another story.

And yes the weight survives grinding and sawing just fine.

Jordan Kube 04-03-2005 11:46 PM

<-------- is not affraid to ask stupid questions. lol

Pete VanderLaan 04-04-2005 12:00 AM

There are very few stupid questions here Jordan but there are different levels of experience . John Croucher and Lani know tons more than I do and even so, I know a lot. It gets good when all of those experience levels come together looking for something everyone wants and can do it without a lot of ego.

Jordan Kube 04-04-2005 12:30 AM

From what you say about your process it seems like you could get along quite well without your dilatometer. You've got a series of tests that can lead you to a conclusion about a particular color in relation to another glass. You then make adjustments based on what you see yes? So how do you quantify viscosity in a glass? Does it need to be?

04-04-2005 12:31 AM

I think that both the ring test and trident seal are behavioral, in that they take into consideration the behavior of the glass in a process including the method of annealing used. What is hard here is that they require annealing which is hard to wait for when you have a tank of glass and color to use. I also agree that the pull test makes the most sense with the least variables, which is the case a lot of the time when adding color to batch. You have limited things to change. Who knows what the variable are when the bar formula is inknown? Survival is the test. The ring test is probably the quickest test of survival.
So Pete, what is the quickest ring test method? If the wall thickness is less that some measure, can it be cooled in say an hour or two and still be meaningful. This does not reproduce the actual annealing that might be used but gives you something to look at before lunch. Can we get down to what you call a useable methodology?

Jordan Kube 04-04-2005 12:49 AM

When I worked for the venerable Ed Skeels he had a pretty good method. Blow a thin cylinder, anneal, score with a diamond point and watch to see if there was a gap or an overlap. Ed would measure the thickness of the cylinder and the gap or overlap with a micrometer and record the measurements. They were pretty thin and I think he annealed them pretty quick.

John Croucher 04-04-2005 04:41 AM

Hugh, the trident seal test takes no longer than a ring test .In the case of a paper weight created for the saw test much more. Both need to be annealed, but if the samples are thin -ie around 2 mm or 1/10th of an inch or less, its all over in under 90 minutes. The trident seal advantage is that it is easier for a neophyte to get more acccurate results. Getting the ring test to have equal thicknesses of both glasses is quite difficult and equal thicknesses of both glasses are critical for an accurate outcome. The fusers all have a reasonably equal sheet glass thickness to work with.

The trident seal test allows a quiet and unhurried measurement to take place with the accuracy of a micrometer before fusing the respective glasses, whilst overlays circling around a glory hole don't. Ed Skeels or Lino or Peter V may be able to do overlay ring tests with the respective glasses thicknesses within 0.1mm of each other, but I would wager most glass blowers can't. Pete V rails against the trident seal test as being too sensitive, but in our experience it can accommodate a difference of 200nm/cm, which for most glasses is around a 4-5 point difference. That's a wide enough gap to test for and make adjustments. Some glass formulations are really peculiar. For instance, a fluorine opal glass with around a 20% PbO content is unbelievably unresponsive to react to an alkaline addition or subtraction re nm/cm. What we thought would require a chemical addition of 1-2 points LEC required an 8 point addition on our chemical spreadsheets. Some glass families adjust really rapidly to minor alkaline additions or subtractions, others require major alterations. Actually, outside of our measured clear glass parent families, I don't care what the measured LEC'c are of our 9 glass matrices are. All we care about is whether all the glasses fit each other. within an annealing range of 470oC -5202oC.

The other thing I forgot to mention in my earlier post is how critical the temperature range is when LEC measurements are concerned. Theoretical comparisons are useless when comparing English and Turners factors with Appen or when real world actual measurements are concerned. Most of the C&R Loo published results are either theoretical or voodoo nonsense. E&T worked everything out over the range 25-90oC. Appen calculated all his factors over 20-400oC. In Woolley's invaluable monograph, SP87 measured 94.9 over 0-300oC and 97.8 over 25-300oC. The E&T numbers come up at somewhere around 88-99. Quite a big difference. Corning uses a US$50,000 Theta dilatometer that has no better than +/- 1 LEC point accuracy, so even there the numbers are vague. That's why we say AROUND 96 x 10-7 over 0-300oC with our standard with an annealing temp of AROUND about 490oC . It's in the ball park but no more.

Dave Bross 04-04-2005 10:20 AM

Along the lines of suggested simple and quick in studio "ballpark"sorts of tests, here's a little back yard/shade tree upgrade for the thread pull test that has done good things for me in helping repeatability.

I've been using approx. 1/4' wide strips of sheet glass that match the expansion (and are pretty close on viscosity because they're the same general sort of glass) of what I'm shooting for, Spectrum 96 for 96, Bullseye for 90, Moretti for 104.

With a torch, I can easily heat, apply, and flatten out with tweezers, an equal amount of the mystery glass to the glass that is below it in the strip of known expansion. From there, heat it until it balls up and pull. I shoot for the same length of pull to also help consistency. I'll also pull a thread test between the actual glasses I'll be using because even though glass A may fit glass B, and glass C will fit glass B, it doesn't mean that glass A will fit glass C for all the reasons we have been discussing in this thread.

I've got it to where with my spreadsheet results, this technique, and whatever other dark of the moon factors reside locally, I can pretty reliably say that 1mm of bend in 200 mm of thread is just about .6 to .65 in expansion in my spreadsheet, which is conveniently just about what a pound of sand (in a 100 # initial recipe) will move the expansion in a basic soda lime sort of glass. Your mileage may vary.

Final check is a homemade polariscope (two polarizing lenses from cameras, cost $20 from Ebay) used on a section of glass containing the two glasses cut from whatever application they are destined for.

I've come to know from experience how much stress will pass in which application and I'm always working to dispose of even small stresses in the next go-around. There's an article over at the warm glass board on compatibility that has pictures of a chip and bar test in various stages of stress. This was what I initially used to "calibrate" my eye as to what I was looking at in terms of stress levels.

I can't get good results with this if one of the glasses is lead. I'm trying to wean myself from lead anyway, so not terribly critical for me.

I can get pretty good results in the striking glasses if I simulate all the strikes that will happen in the course of working out the glass by reheating the sample as many times as it will strike in the particular process where it will be used, including one for the anneal.

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