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Tips, Techniques, and Questions -- Technical questions or tips

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  #1  
Old 2013-11-13, 3:56am
kmd kmd is offline
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Default COE question

I was just wondering........what determines the manufacturer's choice to make their glass of a particular COE?

Is there any perceived difference between the way different COEs behave?

Yes,I know you can't mix COEs. But , dream on, wouldn't it be great if ALL soft glass had the same COE and we could use ALL those yummy colours?

So, is this likely to happen in our lifetime?
KMD
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  #2  
Old 2013-11-13, 6:49am
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Originally Posted by kmd View Post
So, is this likely to happen in our lifetime?
KMD
No. The only way to use all those colors is to stock up a variety of each COE. Most glass is manufactured for other purposes than lampwork. There is no motivation for them to change.
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  #3  
Old 2013-11-13, 1:49pm
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Well, there's never going to be one COE for all glasses. But if you're really clever I bet you can come up with ways to make things out of different glasses and put them together - they don't necessarily need to fused together. Graded seals can be used between glasses that are close together like 96 and 104 if it absolutely needs to be a continuous piece.
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  #4  
Old 2013-11-13, 3:23pm
28676bhe 28676bhe is offline
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What is a graded seal?
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  #5  
Old 2013-11-13, 3:36pm
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It's a part of a glass piece that's made with mixing two glasses of different COEs gradually, to bridge the gap between the two glasses. The way I've seen it done is by layering the two glasses in several layers, pull into a rod and use to make the seal.
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  #6  
Old 2013-11-13, 5:05pm
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Thanks, Anne!
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  #7  
Old 2013-11-18, 3:26am
kmd kmd is offline
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Default Different COEs

Still curious to know. WHY does soft glass come in different COEs?
Are some colours easier ? Do different soft glass COEs behave differently?
Is there a glassy guru who understands the chemistry who can explain?
KMD
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  #8  
Old 2013-11-18, 12:50pm
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It starts with the basics soda lime and borosilicate. Do some research on each product and you will then understand because it is all about chemicals and compounds and the info is extensive.
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  #9  
Old 2013-11-18, 2:17pm
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Not a glass guru, but in nutshell the different chemicals that go into the makeup of the glass affect its expansion rate. Even glass rated at the same COE can be incompatible. Take a look here for a more detailed explanation: http://www.santasbling.com/index.php...stry&Itemid=53

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  #10  
Old 2013-11-18, 4:04pm
De Anza Art Glass Club De Anza Art Glass Club is offline
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I lost my original post, so I'll try again, more briefly:

The different COEs probably originated by region and purpose.

The Romans worked with glass after bringing the technology from the Middle East. A glass with COE 96 ended up being used for furnace work and COE 104 for lampwork. Originally lampworking torches/burners were some fuel and air, so perhaps the glass with a lower melting point was a later development. There is a book, The chemical history of glass that explains how the different raw materials available affected the composition of glass. (I don't remember the author, but the publisher is Springer.)

Bullseye manufactured stained glass, and worked with glass artists to develop a line of glass that fused together reliably. Their formulations ended up with a COE of about 90. Bullseye doesn't prefer to talk about matching COE, but rather about compatibility, which takes into account the coefficient of expansion, viscosity, and other characteristics of the glass.

Spectrum and Uroboros also made stained glass. Spectrum also made furnace glass, so when fusing became popular, they probably chose to continue with COE 96. Later, Spectrum and Uroboros came up with the "System 96" standard.

I can't find a history of Satake glass (COE 113-120), but I suspect it is a later development to make flamework easier to accomplish with the Japanese air-gas burners. I believe the lower melting point is achieved by a greater percentage of lead in the flux.

I have not found why Schott chose to use a formulation with COE 91. It was probably developed for laboratory glassware, before the development of borosilicate glass.

Last edited by De Anza Art Glass Club; 2013-11-18 at 4:29pm.
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  #11  
Old 2013-11-18, 6:38pm
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Why wouldn't there be glass with different COE's seems to be a better question. Yes, they have different working characteristics, and lampwork is a tiny segment of the glass world - there is industrial, scientific, decorative, household, fusing, casting, commercial, etc. etc., and a lot of it can be used to make beads. The subject is complex, too much so to really cover in a forum post. There is a ton of literature to explain it out there, technical, academic and art based, if you want to really pursue an answer.
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  #12  
Old 2013-11-19, 3:38am
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Thank you for some fascinating reading which has certainly fed the brain and broadened the horizons. Much appreciated.
KMD
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  #13  
Old 2013-11-19, 2:06pm
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I know many of the 96 COE's are made into very large rods primarily for the glass blowers. The colors, especially the transparents, are very saturated because blowing them into larger items dilutes the intensity of the color. Some are nice enough to also offer smaller rods for lampworking, thank goodness
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  #14  
Old 2013-11-21, 1:08pm
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Quote:
Originally Posted by echeveria View Post
Why wouldn't there be glass with different COE's seems to be a better question. Yes, they have different working characteristics, and lampwork is a tiny segment of the glass world - there is industrial, scientific, decorative, household, fusing, casting, commercial, etc. etc., and a lot of it can be used to make beads. The subject is complex, too much so to really cover in a forum post. There is a ton of literature to explain it out there, technical, academic and art based, if you want to really pursue an answer.
Basically, yes, what Kathy said.

With the exception of the 33 COE borosilicate glass used for making laboratory apparatus, it has primarily been the explosion of the art glass market over the last 30 - 40 years, and specifically the market for different colored glasses, that has prompted the present COE "standards". The main reason being that if you make your own glass you can adjust the compatibility however you need to. But if you have to buy your glass from different sources - as the vast majority of glass artists do now - it helps a great deal if those different glasses fit together. If enough potential customers pressure a manufacturer to conform to a certain standard, and the market is large enough that the manufacturer feels it's in their financial interest to do so, they will usually will. That pressure is pretty much why we now have the COE "standards" we do. (Which is a misnomer in itself, because COE isn't the only important issue in compatibility. Strain point - AKA: viscosity - is nearly as important. An example of this is the 90 COE "standard" commonly quoted for Bullseye "Tested Compatible" glasses. In reality, these glasses are not all 90 COE. Some of their COEs are intentionally higher or lower in order for the various colors to be compatible with each other.)

33 COE happens to be the expansion of Corning's code 7740 Pyrex that has been used by laboratory glassblowers for 100 years. Because 7740 was the first widely used borosilicate to market, it became a standard. (Although Schott actually came up with low expansion borosilicate first.) The various boro color manufacturers that have blossomed over the last 30 years have naturally conformed to this existing standard. It would be financially stupid not to.

90 COE glass has been around for a very long time. It is the approximate expansion necessary to make the glass to metal seals required for light bulbs and vacuum tubes. It is also roughly the expansion of window glass and container glass, and a point where there is good compromise between meltability and chemical durability. It has become an art glass standard primarily due to Bullseye developing their Tested Compatible glass at roughly this COE. Like the boro makers, in order to conform to the existing market, subsequent fusing glass manufacturers followed suit with their own glasses in this range.

96 COE as a standard has a more recent history that can be traced to the widespread availability of pre-mixed glass batch for use by studio glassblowers. Somewhere around 1980, as studio glass was becoming very popular, Spruce Pine Batch began selling a glass batch to studios that was developed by glass chemist Dominic Labino. Although they actually make the batch in three standard expansions, it was their 96 COE one (called SP87) that caught on, probably because it fit the widest range of European color bar. (The "87" designation is the calculated COE when using the popular English & Turner expansion factors.) Once again, because it was first to market, and thus held the widest market, it has become a de facto standard, even if a lot of the color manufacturers that were already in business have been late to the party.

104 COE? I'm not sure, except that this happens to be roughly the expansion of Moretti lampworking glass, which has been around for a very long time. As was surmised earlier, this higher expansion was probably settled upon due to it's easy melting in a torch flame. Most lampworking torches in the past were gas/air, rather than the higher temperature gas/oxygen we now use.

In reality, glass expansions run the gamut from zero (titanium silicate glass/ceramic) to over 120 (Sataki).

So that's my glass history contribution for today. Time for me to go do some actual work before my studio becomes history because I can't pay the bills...

Brad
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Last edited by glassmaker; 2013-11-22 at 2:55am. Reason: Fixed typo, changing code 7730 to 7740.
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  #15  
Old 2013-11-21, 1:58pm
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Bravo Brad! Nice summary.
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  #16  
Old 2013-11-22, 6:47am
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Thanks for the info.
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  #17  
Old 2013-11-22, 7:48am
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It took me so long to answer Kristin's first question yesterday, that by the time I was finished I forgot about the others. Here are the answers to those as well.

Q: "Is there any perceived difference between the way different COEs behave?"

Yes. Generally speaking, the lower the COE the stiffer the glass, i.e., the higher the working temperature. That isn't universal, but it is usually the case.

Q: "I know you can't mix COEs. But , dream on, wouldn't it be great if ALL soft glass had the same COE and we could use ALL those yummy colours? So, is this likely to happen in our lifetime?"

Not a chance.
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  #18  
Old 2013-11-23, 11:08am
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Wow--I've learned a lot in this thread. Thanks!
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  #19  
Old 2015-05-10, 11:55am
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Default Graded Seals

OK you can get away with a difference of 4 coe's. In other words 92 is compatable with 96. When a glass company calls their glass 96 coe they
actually mean 92 to 96 it's not a rigid 96 depending on the color etc. To seal a 33 coe boro to an 8 coe quartz glass you need an intermediary or several between both the glasses that will work with either on either end. Graded seals are used mostly in scientific glass blowing for apparatus manufacture. A scientific glass blower would add this technique to his resume. For instance a 33 boro pyrex is rated as 7740 but there are other ratings as well including 7736 and so on down until the correct number is reached to join the two.

There are other problems that may hinder you in joining two glasses together as well. One would be the viscosity of the two glasses. If one melts and flows easily and the other not they may not work together. If you are unsure just do a simple test by joining the two together overlapping the ends and stretching that part of the mix out to a stinger. if parts flake off or the stringer coils up or forms curve they are not going to fuse well. If the stringer stays intact and stays straight then there is a good chance they will.
Or you can just have fun and forget all this tech brew ha ha,Wayne

P.S. Pyrex 7740 was actually invented for railroad train lanterns as it was not subject to thermal shock when being struck by rain.

Last edited by hyperT; 2015-05-10 at 12:01pm.
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Old 2015-05-10, 12:45pm
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Quote:
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OK you can get away with a difference of 4 coe's. In other words 92 is compatable with 96. When a glass company calls their glass 96 coe they
actually mean 92 to 96 it's not a rigid 96 depending on the color etc. To seal a 33 coe boro to an 8 coe quartz glass you need an intermediary or several between both the glasses that will work with either on either end. Graded seals are used mostly in scientific glass blowing for apparatus manufacture. A scientific glass blower would add this technique to his resume. For instance a 33 boro pyrex is rated as 7740 but there are other ratings as well including 7736 and so on down until the correct number is reached to join the two.

There are other problems that may hinder you in joining two glasses together as well. One would be the viscosity of the two glasses. If one melts and flows easily and the other not they may not work together. If you are unsure just do a simple test by joining the two together overlapping the ends and stretching that part of the mix out to a stinger. if parts flake off or the stringer coils up or forms curve they are not going to fuse well. If the stringer stays intact and stays straight then there is a good chance they will.
Or you can just have fun and forget all this tech brew ha ha,Wayne

P.S. Pyrex 7740 was actually invented for railroad train lanterns as it was not subject to thermal shock when being struck by rain.
Good stuff here. In my experience though, when color manufacturers talk about 96 COE there is a +- tolerance so 92 - 100 is possible. I think this is why there can be issues within a given mfgrs pallette.
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Old 2015-05-10, 2:09pm
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For me it is an issue of first, recipes and second - marketing. Or may be vice versa. But anyway - if, say, Spectrum is successfull in fusing glass with their system 96 for fusing it is much easier (and reasonable) to add rods to the assortment than to go into competition with Bullseye or Uroboros in 90, where BE is very good as well. Both companies produce glass of high quality but the buyer will stick to one of them or pay both - no other way out. 104 comes from Italy - probably there was different sand, additives, the development of the craft in general. But the competition in 104 makes me guess that this issue heavily depends on the colour pallete and cost of introducing new or unique colours. COE is not an absolute value anyway, it is approximate always, compatibility is what really matters.
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Old 2015-05-10, 2:43pm
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Quote:
Originally Posted by Katia View Post
For me it is an issue of first, recipes and second - marketing. Or may be vice versa. But anyway - if, say, Spectrum is successfull in fusing glass with their system 96 for fusing it is much easier (and reasonable) to add rods to the assortment than to go into competition with Bullseye or Uroboros in 90, where BE is very good as well. Both companies produce glass of high quality but the buyer will stick to one of them or pay both - no other way out. 104 comes from Italy - probably there was different sand, additives, the development of the craft in general. But the competition in 104 makes me guess that this issue heavily depends on the colour pallete and cost of introducing new or unique colours. COE is not an absolute value anyway, it is approximate always, compatibility is what really matters.
All of the Spectrum glasses are 92 to 96, tested compatible or not. It's just another way to help you spend your money, as far as lampwork goes anyway. LOL
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  #23  
Old 2015-05-10, 3:22pm
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The traditional blowing color like reichenbach and Kugler are +-. Gaffer seems to be tighter with better quality control. Boro seems to be all over the place
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