Archive for the ‘Types of Glass’ Category
What is Glass COE?
So what is glass COE? You see it listed in auctions and Etsy, you hear references to COE, but what does it mean? Let's talk about it, and why it's important.
What is Glass COE?
COE, when talking about glass, stands for coefficient of thermal expansion. In other words, how much and how fast glass expands and contracts, based on its makup. Since different kinds of glasses do use different ingredients, each rod of glass has its own rate.
In general, you'll most often see the following COE numbers:
- 104 -- soft glasses like Effetre, Vetrofond, Lauscha, Double Helix, CIM, Precision...I could go on and on. It's by far the most popular type of glass for lampwork beadmaking.
- 96 -- Uboros, System 96 and CIM are three names you'll see most often, but there are others. And while some people include the Zimmerman and Richenbach glasses here, they really do have a COE closer to 94.
- 90 -- Bullseye is the glass of note here.
- 33-34 -- Borosilicate. Also known as pyrex and boro. Northstar, Glass Alchemy, Momka's are three of the top names in colored boro, while Simax and Pyrex are two of the clears.
- Other -- This category includes the real softies like Satake and Kinara, plus Czech (Ornela) glass. They have COEs anywhere from 106 though 120.
Glass Rods, Mostly COE 104
The most important rule if you don't want broken beads: do not mix glasses of two different COEs in the same bead. Although shortly you'll see some exceptions to this rule.
COE Versus Viscosity
Now if COE was all you had to worry about, life would be grand in the bead-making world. But sometimes you'll find that two glasses with the same COE don't play nice together. And the culprit is usually viscosity.
I have a hard time explaining viscosity with how it relates to glass, so I'll use an example with foods. Take a tablespoon of milk and a tablespoon of honey and pour them into a bowl. The milk pours out quickly, while the honey takes its time oozing out of the spoon. The honey is more viscous than the milk.
(Okay, it's not a perfect example, but now you can get a mental image of viscosity.)
A good glass example of viscosity is comparing Effetre pastel white against Lauscha clear. Effetre pastel white melts fast and can get drippy very easily. Lauscha clear is much stiffer and is more like honey when it melts.
While I don't know for certain, I suspect that viscosity effects COE; in other words, a more viscous glass has a lower COE. And within a glass type (example, glass with a COE of 104), the tolerance is generally 2 points. So what that means is that a glass can be labeled 104, but actually have a range of between 102 and 106.
So, if you combine a 104 glass that's actually 102 and a 104 glass that's actually 106...you get incompatibility and a cracked bead.
Is it Ever Safe to Mix COEs?
I want to say first off is that there is a lot of controversy over this. Some say that you never, ever want to mix glasses of two different COEs, even in minute amounts.
Others say that it's acceptable to mix a tiny bit of a leaded glass (usually a frit made from a 94-96 COE glass) with, say, a base bead of 104 glass. The emphasis on the word tiny.
The only thing I can say about this is from my own experience as a bead-buyer and a bead-seller. I have beads from around 2002 that have some frit on them that appears to be the 94-96 glass that are unbroken. I have made beads that include a tiny bit of 94-96 COE glass that for 5 years haven't cracked or split.
Does that mean they won't crack or split 20 years from now? Don't know, but you can check back for a report then!
In my case, I work mostly with COE 104. Therefore, I label each and every rod that is not COE 104 with its color and COE. Glass can all look the same after awhile; best to play safe.
Well that's it for today with the topic of "what is glass COE". Here are some examples of lampworking glasses in various COEs and colors.
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 Glass Rod Flint 5mm od x 295L 5 lb approx65 pcs  US $25.00
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 Glass Blowing Boro rod Tubing Beginners Bundle Lampworking US $23.25
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 Northstar glass glasstique off color rod glassblowing US $29.95
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 13mm glass rod US $30.00
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 104COE Moretti Randomly Selected Glass Rod Assortment 15 Pounds 65 SALE US $183.25
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 Glass Lampwork Bead Making Design Kit Tool Glass Rod DVD Torch DIY Fireworks Lot US $189.99
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 Mercadante Cobalt Blue Borosilicate Glass Rod 1lb 25mm US $.99
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 Bullseye Glass Transparent Rod 1 4lb COE 90 Lampworking US $6.63
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 Bullseye Glass Opalescent Rod 1 4lb COE 90 Lampworking US $6.63
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Different Kinds of Bead-Making Glass
If you've not made beads, you may be wondering about the different kinds of glass you read about. For example, borosilicate, Moretti, reactive, etc. What is the difference in the kinds of glass? Let's talk about it!
Is There a Difference?
Boro Beads "Sunfire" (Click for larger image)
There is definitely a difference when a lampworker is making a bead. For example, borosilicate ("boro") glass takes more heat and higher kiln temperatures to make the beads. On the other end of the spectrum is Check soda glass, which is almost drippy to work with (but comes in such luscious colors).
So temperature in making the beads is one thing. But what about just buying the beads -- do the various glasses make a difference? In a word - yes.
Bead Glass Colors
Here's something interesting -- some colors are really hard to produce in some types of glasses. For example, a true peach color is next to impossible in a Moretti-type glass (COE 104 for you lampwork mavens). A true pink is also hard to achieve. Not to mention a royal purple!
So one difference is color -- certain colors need specific kinds of lampworking glass. And some colors are more expensive for a lampworker to buy, which may translate into a higher price per bead or bead set.
Irridescent Beads
Irridescent Glass Bead Set (Click for larger image)
Some beads have an irridescent shine, which is sometimes referred to as an "oil slick" look. The shine can reflect one color or many colors, depending on the viewing angle.
These beads are made from what is called "silver glass". Which basically means that varying amounts of silver are included in the glass along with different color elements. And the result? Glorious!
The picture to the right demonstrates that wonderful range of metallic colors that can be achieved with silvered glass.
What About Boro?
Boro is such a different glass that it really deserves its own post. And although many of the special effects that used to be the domain of boro can now be produced with 104 COE glass, boro still has its own uniqueness.
I think that for any bead that has super-thin spots or has an organic shape, boro is the way to go. Boro is stronger than regular glass (think Pyrex), and can handle a little more wear and tear. Still, it is glass, and as glass, it can break, so keep that in mind if the glass will he handled a lot.
Different Bead Making Glass Results
While each glass type has its charms, as well as flaws, there's one thing they all have in common. And it's that the beads made from them are beautiful, each in its own right.
While I tend to favor the silvered glasses when lampworking, I love collecting beads of every sort. From plain to fancy and everywhere in between, they are miniature works of art.
And in addition to what you see below, here's a link to .
I'll leave you with some more eye candy, in the way of bead auctions. Feel free to click for larger photos.
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 PIKALDAhandmade lampwork 8 beadsPINK ROSE BUBBLESRA US $25.00
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 ROA Lampwork 10 Pink Handmade Art Disc Glass Beads SRA US $8.24
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 BG Designs Handmade Lampwork Beads Pink Beach Glass 75 US $35.99
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