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Jabos And Coe Issues

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Thanks for showing sincere interest in the subject Lou, I think this is something that really needs to be understood.

Lou asked for more info on glass compatibility issues so I will do my best to help.

To better understand compatibility, let’s consider what happens when glass gets heated in a kiln. Like many other substances, glass expands when it gets hot and contracts when it cools. This change in density, which occurs at the molecular level, can be measured in a laboratory. A typical one inch piece of Bullseye brand glass, for example, will expand 0.0000090 inches for each 1 degree Centigrade increase in temperature.

This rate, which is commonly known as the Coefficient of Expansion (COE), is usually expressed as a whole number, rather than as a long decimal figure. Most Bullseye glass, for example, is said to have a Coefficient of Expansion of 90, and you will often hear glass artists refer to it as COE90 glass. Spectrum, another common glass, has a COE of around 96, while Corning’s Pyrex glassware has a 32 COE. Standard window glass, referred to as "float" glass by the glassmaking community, has a COE that is usually around 84-87, while Effetre (Moretti) glass, commonly used for lampworking, has a 104 COE.

These differences in expansion and contraction may not sound like much, but they are very significant on the molecular level. A 10 inch length of Bullseye glass, for example, will shrink about 0.046 inches (about 1 mm) in cooling from around 950 degrees Fahrenheit to room temperature. By contrast, a 10-inch piece of Spectrum glass will shrink about 0.049 inches over the same temperature range. That difference - .003, or three thousandths of an inch - sounds trivial, but it’s enough to ensure that you can’t fuse Bullseye and Spectrum together.

You can sometimes get away with using two different glasses where the COE is only one or two apart (say, a 90 with a 91), but not always. Sometimes even two glasses with the same Coefficient of Expansion can not be fused together. That’s because the laboratory test that determines COE takes place at a different temperature than the one the warm glass artist often uses.

There are really only two ways to know if your glass is compatible:

• Use glass that has already been "Tested Compatible" by the manufacturer.

• Conduct compatibility testing on your own. This is a matter of fusing small squares of the glass to be tested to a base glass of known COE, then examining the fused strip by sandwiching it between two strips of polarized film, this will show signs of stress and tension within the glass itself and between the incompatible glasses.

Some of this info was taken from text books on art glass and websites, no intent to infringe on copyrighted materials, this is simply my best effort to educate those who actualy care about what can happen and in fact what is happening to some of the modern Jabos esp. the aces and those containing gold aventurine.

As a professional glass artist I can't help but speak my mind when it comes to good glass vs. bad glass, a slight example of "bad" glass would be a series Blenko wanted to make, they wanted to apply a blue thread on their amber glass, even though the items produced looked stunning at first, they soon showed compatibility issues and the idea was scrapped, not one piece of that glass was sold, Blenko being wise enough to know that if that product hit the market there would surely be serious backlash and legal issues.

I do not know exactly what colors were used, all glass color makers such as Reichenbach, Gaffer, Kugler and Zimmerman all have detailed info on the colors they make, Bullseye, Morretti and Spectrum glass also have this info available for good reason.

Gold aventurine is probably one of the most troublesome colors, used carefully it will shine bright and last forever, if used in excess it will surely cause failures, I have tryed just about every color cobination possible in my 20+ years of glass, every failure is logged and I refrain from making the same mistake twice.

I currently use 149 different colors including 5 different aventurines, I know what I can mix and what I can not.

I have also used marble cullet from all but one manufacturer (Peltier) to blow small vases etc. even though the color may be from the same factory does not mean the glass is compatible.

I hope this info is helpful and the makers/investors and sellers start to show some responsibility for the product they produced.

I hope anyone who has bought "bad" glass stands up and demands their money back or file due complaints with the proper authorities.

The world has become a sad mess of greed vs. profit, as an idividual I can do little, as a group we can make changes to protect ourselves from those who want our money.

In the end I will say this............. Don't be blinded by beauty!


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I got a set of ACES from Marblealan. When I opened the box, one of the JABO's was split in half and smooth. It was a simple one, sort of like Stephs avatar shot. This is a compatibility issue for sure.

Hopefully there is some sort of testing done before everything was thrown into the pot.

Let's keep this thread civil, as this is very important to the longevity of the later multi-colored JABO marbles.


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Another thing to consider is the fact that the marbles have not been properly annealed, in effect you are "tempering" the glass by removing the tempurature stresses of different colors and glasses, slowly cooling it past the strain points to a stable structure. To do this the glass must be placed in an oven before it falls below 850 degrees, this is nearly imposible as marble screws typicaly cool the glass below 850 even when the screws are preheated, I know this as I have rebuilt and used a 1934 Vitro marble machine, I have experienced what happens in a controled environment.

Marble manufacturers do not actualy anneal the product, they simply let a bin or bucket fill up and put it away to cool on its own, this method has it's flaws as some of the marbles in every bucket or bin will fracture due to cooling too fast, this is totaly acceptable as this is the method used for many years and evident by the amounts of "cull" found at every marble site, cull being the marbles that didn't pass QC and were NOT TO BE SOLD.

The only way to prevent annealing issues is to properly anneal each and every piece of glass, any piece of glass that has not been cooled correctly can and in most cases will fracture when all the atmospheric conditions are right.

Has anyone ever had a paperweight suddenly pop in two? Paperweights made in the glass factories by workers on their breaktimes etc have been typicaly cooled in vermiculite and sometimes even warm sand or other insulating materials with the intent of slowing the cooling rate, this is sometimes effective depending on the conditions, however, if you take one of those paperweights made 50 years ago and look at it under labratory equipment will shows signs of heavy stress just waiting to be released.

Again I'd like to say the new Jabos sure are pretty, just be aware that some factors are taking effect.


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Not to add to the confusion but rather to help explain it a little more....

Lots of times you will see folks "sculpting" glass on the streets making various items.

Roses, wizards, sun catcher's, etc.

Typically EVERY time they are using borosilicate or pyrex glass, which as Scott explained fairly well is a specific COE.

This glass, (the same stuff you use in your kitchen pans) is VERY hard and can take a LOT of stress.

That is why you can see many of the glass artist make a glass item and leave it to cool down on their graphite slab that they work on.

It is NOT annealled, however, normally if the temperature is not too cold, it will be ok and will never show fractures because it has cooled down slowely enough to not stress the glass to the point that it will break.

One of the main reasons is the thickness being made. It is normally not that thick and can cool down rather evenly.

However, a marble on the other hand is really thick in comparison, even a 3/4" size probably will fracture if not cooled down evenly and slowely

as Scott has previously said.

The compatibality issue especially with the aventurines and goldstone (Lutz) is that it is normally so soft that it is virtually impossible to anneal evenly.

Here again a main consideration being thickness as it is used sparingly (due to cost) and even if just on the surface will cause too much stress in the glass for some fracturing, or "checking" of the glass not to occur.

It can be said that it is the effect the artist was looking for. I would have to say that is what was decided to say after the fact when the fracturing or checking showed up and they did not want to throw it away due to losing too much money.

As I am not a glass artist, but a hobbyist I get to play with the glass. I do not have to make glass that will sell.

I get to make LOTS of tests and mistakes and like Scott I catalog them so when we do start to make marbles we want to sell, we know what glass we can use, normally how thick we can get away with its use, even if we can use it on the surface and not the interior or vice versa.

Fractures are BAD glass.

If you pay for "broken" glass, (except crackle glass, which is A highly refined technique) you are buying someones mistakes.

Either bad compability or not enough annealling. Regardless, it is still bad glass.


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Thanks Bo, John and Lou.

It's good to see some people do understand the point I was trying to make. I was not trying to make enemies nor was I saying they intentionaly did any wrong, mistakes happen, deal with it like an adult, accept the facts given to you and handle them in a responsible manner.

They did a fine job at making pretty little glass balls and I don't doubt it was fun doing it, I would do it too if given the oportunity. but, if there became a problem, I would simply deal with it and not sweep it under the rug, it's called responsibility.


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