System 96 - Common Questions and Answers

Why did you choose a "96" C.O.E.?
The Spectrum line of stained glass products was formulated to the nominal "96" expansion long before we elected to manufacture a Tested Compatible line for kilnforming and other Hot-Glass work. We chose the "96" Expansion because it facilitates the creation of glasses with "friendly" forming characteristics. The wide variety of glass types we manufacture demands a formulation that has great flexibility.

Because many other glassmakers, as well as suppliers of blowing batch, frit, color bars, etc., chose "96" for similar reasons, we decided to build upon this "family" rather than reformulate our products to the C.O.E. "90" range.

What's the difference in kilnforming at "90" and "96"?
Really very little. What you learn with one glass will largely apply to the other. System 96 is a lower temperature glass -- that is, it takes less time / heat for S96 products to reach a given viscosity than it does common COE 90 products. Understanding this, and looking over the S96 Firing / Annealing Guidelines, a kiln crafter will quickly adapt to the differences.

What do you mean by "working range"?
To blowers and other manipulators of hot glass, this means more time in that "sweet spot" of temperatures where the artist can affect the glass. A "longer" glass offers more tolerance and freedom for creativity. Glass fusers will discover a wider range of temperatures between "not-yet-fused" and "beyond-full-fused," thus greater freedom in forming and a wider margin of error. Glasses with a shorter working range "set up" or "freeze" faster than "longer" glasses.

What about devitrification?
All System 96 products have been specially formulated to resist devitrification. That, plus compatibility testing, is what makes them different from other Spectrum glass products.

What about Iridescent Glass?
System 96 Iridescents are manufactured and sold by Uroboros Glass Studios. There is a broad range of iridescent textures to choose from, and all withstand full fusing temperatures. They are stocked by all System 96 distributors.

What does Uroboros have to do with Spectrum?
Uroboros is one of our System 96 Compatibility Partners. They make System 96 Tested Compatible specialty colors and textures, Iridescent glass, Frits, Stringer, Noodle and who-knows-what else.

How about Thin glass?
At this writing, Spectrum supplies an "Ultra Smooth Thin" in both Clear ( #X1002M) and Black (#10092M). Uroboros supplies 1.6mm hand-rolled thins in both clear and black (#61-00-96 and #61-56-96, respectively). Additional thins may be added at a later date.

Should I Still Test?
Testing is a good idea, and we will continue to recommend it, even for "Tested Compatible" products. Testing is your best teacher. You'll discover subtle nuances in different glasses, monitor color shifts, and be better able to predict various characteristics that may result from the fusing process. Plus, because our equipment and procedures differ from yours, you just might uncover a set of circumstances in which our "Tested Compatible" glasses don't act as expected in your system of variables. Better to discover that in testing than in a disappointing project.

With Spectrum System 96 glass, all glass of the same stock number from the same production day will be dependably identical. There is no meaningful variation in C.O.E. or other characteristics within a production day.

System 96 products are supposed to be cheaper but it doesn't look that way to me . . . what gives?
Most "90" C.O.E. products are priced and sold by the pound. System 96 sheet glass is sold by the square foot. Glass priced at $10.00 per pound is actually about $17.00 per sq.ft (1 sq.ft . weighs about 1.7 pounds). Make sure to convert pounds to sq.ft (or vice versa) to make a fair comparison.
To convert $ per pound to $ per sq.ft : multiply by 1.6
To convert $ per sq.ft . to $ per pound: divide by 1.6

Why is a System 96 glass more expensive than the same identical color of regular Spectrum glass?
There are a number of reasons: (1) the agents in the System 96 formula that resist devitrification are considerably more expensive than their counterparts in "regular" Spectrum glass. (2) System 96 products are made in much shorter runs than "regular" Spectrum glass, thus, they are significantly more costly on a per Sq.Ft. basis, (3) the costs of testing, classifying, labeling, etc., and, especially, (4) suffering the costs of making non-compatible glass when only compatible glass will do. It adds up fast. Fore more in-depth information, read our Tech Bulletin #2 "This is Not Your Father's Spectrum Glass," by Gil Reynolds.

How do artists use your "Ultra-Smooth Thin Clear"?
The Thin Clear is a very versatile product. A single layer of design elements "held together" with thin clear creates a finished piece that is lighter and more delicate. Used as a "cap" it adds richness and depth, like a blown glass object being "cased" in clear glass. It is also a useful tool in volume control, helping the artist to equalize glass volume on each layer without making design compromises.

Can Spectrum Glass be used for dinnerware?
Spectrum products have been tested for chemical leaching as required by the FDA for food bearing surfaces. All of our products passed and were determined to be suitable.

However, when you use Spectrum glass to produce a product of your own (slump it, fuse it, foil it, lead it, etc.), it’s not Spectrum glass anymore. It’s your product now, and as such, must pass all tests before being sold or used as a food bearing surface. It is possible that the processes you use to make your product alter the composition of the raw materials (the glass) in such a way that they may no longer meet the required standards. Either way, the regulations are clear: You must have your own finished products tested and approved.

For more information about health and safety issues for food bearing surfaces you should contact The Society of Glass Ceramic Decorators, 888 17th Street NW, Suite 600, Washington, DC (202) 728-4132.

How can I get "fire polished" edges?
Spectrum glass needs to be fired at 1470º for about 10 minutes to fire polish edges.

Can Spectrum be ground into frit & fused on the surface of my project?
Sure. But why not go easy on yourself (and your equipment) and just buy the excellent crushed glass frits supplied by Uroboros Glass Studios? Every System 96 color is available, including Iridescents, in 5 particle sizes, in both 8.5 oz (.24kg) and 4 Lb (2 kg) jars.

Can I fuse with "regular" Spectrum Iridescent Glass?
The "Mother of Pearl" coating on non-System 96 Spectrum Glass will withstand temperatures up to about 1300ºF. While you can produce some very interesting bent and slumped pieces that will retain the iridescent finish, it will burn off of most pieces at full-fuse temperatures. You can maximize your iridescent effects at higher temperatures by fusing with the iridescent surface against the kiln shelf, and by minimizing time spent above 1400º F.

System 96 Iridescent glass, made by Uroboros, will not burn off, even at full-fuse temperatures.

Can I use Spectrum Glass for "Casting"?
There are two methods of casting: hot casting and cullet casting. In hot casting, the glass is heated in a crucible to approximately 2300º F then poured into a mold. In cullet casting, broken glass is placed into the mold first and then fired to about 1600º F or until the desired result is reached. Spectrum System 96 glass can be used for either type of casting. Uroboros Glass has recently added System 96 "Tested Compatible" Casting Billets in Clear and 8 colors. More Info.

What about using Spectrum Glass for bead making and torch work?
Spectrum is a great choice for bench work. Its long working range allows greater artistic flexibility and greater margin or error. Multicolor mixes allow artists to lay two or more colors simultaneously. You can lay more glass faster than with traditional rods and you can incorporate the complete line of compatible Frits, Stringer, noodle and Dichroic glasses.

I've been fusing with Spectrum for years with few problems; why should I pay the premium for "Tested Compatible" System 96?
If you're doing your own testing and require no protection from devitrification, by all means fuse with "regular" Spectrum glass. But be aware that both stress and devitrification, even if not immediately apparent in your finished projects, can cause cracking or surface crystallization over passage of time. So please, when fusing with non-labeled Spectrum products, test habitually and take careful measures to control devitrification.

Kayleigh Clark

Wednesday, January 20, 2021
Delphi Expert
134 Posts
Top Contributor Gallery Artist

@Yes, you can fuse glass to itself. As long as you are fusing the same sheet together. If you are wanting to fuse 2 separate pieces we don't recommend that. Here is a link to our fusing tip sheet.

Kayleigh Clark

Monday, January 13, 2020
Delphi Expert
134 Posts
Top Contributor Gallery Artist

You can use 96 COE glass in a microwave kiln.


Wednesday, October 18, 2017
91 Posts

@It is important to avoid mixing 90 COE and 96 COE glass in a project. The COE is a simplified way of expressing the complexities of how the glass expands and contracts as it is heated and cooled, and a difference in the COE number is meant to mean that they expand and contract at different rates, so they pull away from each other at different points in the heating and cooling process. Sometimes the stress from this is enough to immediately cause the project to break, other times the project may look fine initially, but the internal stress will cause the project to break at some point in the future, often unpredictably.


Tuesday, May 17, 2016
1 Post

Is it true that Spectrum is ending production of their sheet glass?


Thursday, November 5, 2015
91 Posts

@Mary Jane W. while devitrification may be the issue, it most commonly occurs in a higher temperature range than would typically be used for the slumping process. It is not uncommon (especially with clear glass) to be able to see the slight texture that results from contact with the kiln shelf or fiber paper during the initial fuse firing. Once the glass is slumped, the way the light is refracted by the slight texture can make it seem more visible. You can also review your firing schedule to make sure you aren't firing hotter than necessary for your slumping/draping process - you can find some helpful hints at


Sunday, November 1, 2015
3 Posts

I'm not sure if my pieces are getting devit or if I have a different issue. When I slump vases using a clear base, areas of the glass that don't come into contact with the mold look frosted. Is there a coating that I can put on the glass that will fire polish the frosty look out?

Jennifer Bonesteel

Thursday, February 19, 2015
Delphi Expert
188 Posts
Top Contributor Gallery Artist

@pphx Molds are fine to use with 90 COE (Bullseye) or 96 COE. The COE does not affect how the mold works. If you want to use frit between layers of 96 COE glass you must use 96 COE frit or stress fractures can occur. You can always use a clear overcoat to help prevent devitrification but System 96 glass generally does not devitrify so you may find it unnecessary.


Thursday, February 19, 2015
1 Post

I am just beginning to purchase Uroboros COE 96 streakie glass. Are molds that are typically used for COE 90 glass OK to use? If I am using clear frit powder between the layers can I use Bullseye frit, or must I get COE frit? Can I use the clear overcoat to prevent devit? Thanks.


Saturday, June 22, 2013
4 Posts

I figured it out and am on my way to fusing beautiful pieces of glass. It took me playing around with it as all the advise I was getting was not working....but thanks everyone for the advice anyway. :-) Im happy now.

Elizabeth Burns

Saturday, June 22, 2013
Delphi Expert
118 Posts
Top Contributor Gallery Artist

@ElletteShafer If your piece is breaking in two, it sounds as if it could be due to poor annealing. This means that the glass cooled down too quickly. Alternatively, the glass experienced thermal shock from heating up too quickly. I would suggest adjusting your full fuse schedule into your kiln in order to obtain better results. I would change the rate in segment 2 from 600/hr. to 300/hr. 300/hr. is always safer. In segment 3, I suggest switching it from FULL (9999) to 300/hr. as well. Then on last segment, I would switch it from 150/hr to FULL (9999).