[PA-NJ Glassblowers] Spectrum 96 Glass

Tony Patti gaffer at glassblower.info
Sun Sep 23 23:58:49 EDT 2012


While looking for annealing information, I discovered this very interesting web page,

Which I think will be of interest both to warm glass and hot glass folks.

 

Who would have thought that Spectrum 96 manually records 100,000 data points every day about the production from their TEN furnaces!

(see section below which I highlighted in yellow)

 

http://www.system96.com/Pages/KnowledegBase1.html

 


 <http://www.system96.com/index.html> http://www.system96.com/FuseImages/Sys96c.jpg


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Knowledge Base

		

A posting of issues and concerns System 96 users have had, along with our ideas, advice and suggestions. Use your browser's "Find" command to search for keywords relating to the issue your interest.

	

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Q

Why does OpalArt seem to trap and reveal air bubbles more than others?

	
	
A

Because of the very thin layer of intense color on the surface, slight surface distortions are easily exaggerated. This will always be the case with these products.

Solutions: I improved, but did not eliminate "the mottles" by going real slowly between 1150 degrees to 1350 degrees.  I soaked for 10 minutes at 1150, then ramped up to 1350 at 150 deg/hour.  Then soaked for 15 at 1350.  I then quickly went up to the temperature that gave me the fuse I wanted and then dropped right down to 950.

For plates and bowls and whatever, I get perfect results when I only fire a single layer with a two or three layer border built around the dynamic piece of Opal Art.

	
		
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Q

Why do some firing instructions recommend lower full fuse temperatures and longer hold times? One teacher told me to full-fuse System 96 products at 1440 for 30 minutes. I bought a computer program that says 1425 for 75 minutes -- your guides suggest 1465 for 10 minutes. What's the difference?

	
	
A

We like the ultra-gloss top surface that results from higher temperatures. Going hotter and holding for shorter periods also soaks less heat into the kiln shelf and other refractories, allowing for quicker cooling. People that prefer lower temperatures are often using one of the high-tech kiln washes, like Primo Primer. These products get better results at lower temperatures (less sticking and fewer "blowouts.

	
		
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Q

When fusing your OpalArt glass, I find that bubbles sometimes change the surface color of the glass, creating a lighter colored “spots.”  Am I doing something wrong?

	
	
A

OpalArt‘s color swirls lay largely in a very thin layer on one surface of the glass sheet.  When bubbles form, as they are prone to in the fusing process, they can stretch this already-thin color layer, creating a pale mottle.  Use the same bubble-avoidance techniques you normally would, or fuse color-side-down, to minimize or avoid the effect.  Here is our standard text on the subject--

The variegation in an OpalArt sheet rests on top of the base glass surface in the form of a sheer layer of intense color. These thin swirls of topside color are light permeable, and bubbles trapped between project layers can present as antique-like surface mottling. You’ll also find that the bottom side of an OpalArt sheet looks different from the top – sometimes with fainter color streaking, sometimes void of streaking altogether.

	
		
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Q

Sometimes when firing, a hump rises up on the surface of my project, leaving a cavity on the bottom surface. Why is this happening?

	
	
A

We call this an “eruption,” an “uprising” or a “burp.”  There are always expanding gasses between the bottom of your project and the shelf below.   An eruption occurs when these gasses are unable to escape around the edges of the project. The resulting upward pressure deforms the softened glass.  Prevent this problem by holding at around 1370°F for 20-30 minutes during the heating phase. At this temperature the glass is still stiff enough to retain its shape and the gas will have time to find another avenue of escape.

Ironically, this problem is exacerbated by the new high-tech primers, fiber boards and improved shelf papers.  As these products get better at leaving smoother glass surfaces, they also leave less space between the project edges and the separator (the avenues for escaping gasses are fewer and narrower).  More time is necessary. 

	
		
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Q

While firing coasters, using a black iridescent with a clear layer on top, I am getting bubbles between the layers.  If I fire the coasters again the next day, the bubbles go away. I have never had problems with any other type of System 96 glass, what should I do?

	
	
A

You need to turn up the heat. The irid surface is reflecting heat away, so your piece isn’t getting as much heat as you might expect. Run a hotter cycle, both in your squeeze and in your full fuse temperature. The hotter cycle gets more heat to the project and the bubbles should vanish (This is consistent with the fact that the bubbles disappear in your second firing).

	
		
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Q

I am using iridescent glass in thick projects and the irid coating sometimes cracks and separates. We are using the same firing schedule we use for other projects this thick, why is this happening?

	
	
A

Given enough heat, a thicker stack of glass naturally will re-form to about 1/4 inch. The iridescent coating, however, does not stretch as the glass moves and this can cause the coating to tear or crack. You may want to alter your approach, depending on the end result you are after.

	
		
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Q

Do your products offer UV protection?

	
	
A

All glass, even clear, absorbs a significant amount of UV light. Depending upon the base glass composition and the coloring oxides, 70 to 100 percent UV can be absorbed. Generally, greens, yellows and reds absorb more than blues and purples. Cadmium yellows and most chrome greens completely absorb UV radiation.

	
	
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Q

I teach a college stained glass course and there has been a problem with your red cathedral glass turning orange during firing. Not all your red cathedrals do this and I was wondering what the technical cause is and whether there is a cure?

	
	
A

Reds are tricky. Usually our reds fuse a little darker, and sometimes, (less than 10% of our production), will fuse lighter. Spectrum reds hinge on a delicate balance of Cadmium, Selenium and Sulfur. There is less than 0.1% sulfur in the glass formula, and that is key to striking the glass red, orange, yellow or in-between. To make matters worse, sulfur is very volatile, and a large percent of it gasses off when the glass batch is melting. Many variables, including the weather, can effect the sulfur retention during melt. We're proud of our ability to control most of the known variables, but sometimes the Glass Gods like to have their way. Red hue change during reheating can only be minimized by limiting the amount of time the glass spends at high temperatures. Above1200 degrees all those Cadmium, Selenium and Sulfur atoms start knocking around and rearrange their relationships with each other. There is a preference for all the Cadmiums and Sulfurs to hook up together, leaving the seleniums to hook up with any remaining Cadmiums. Depending upon how many atoms found partners, who they partnered with and how many got left standing alone, the result will be a color somewhere between yellow and brown. See also . . . <http://www.system96.com/Pages/KnowledegBase1.html#StrikingHots> 

	
	
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Q

I am curious if you use SPC to control the quality of your glass products. What is most critical in assuring the glass is "compatible" for fusing?

	
	
A

We have toyed with Statistical Process Control, but what ultimately defeats our efforts is the fact that stained glass is an art product; good and bad art is in the eyes of the beholder. Not that we don't record daily production variables. We're the "NASA of stained glass manufacturers" according to Ed Hoy. We manually record over a 100,000 data points daily. We have production efficiency measures for every product. But our SPC is really "Subjective Process Control".

What is most critical to assure compatibility of our fusible glasses is seeing very little to zero stress in our daily compatibility tests. Many glass samples from all ten of our furnaces are tested daily against our 100sfs standard. Both high temperature viscosity and the coefficient of thermal expansion need to be similar to assure compatibility.

	
	
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Q

Are projects made with System 96 glass "dishwasher safe"?

	
	
A

Hmmmm. Let's put it this way: System 96 glasses were not designed to stand up to the stresses of modern dishwashers. However, we know people (reliable sources) who swear they've been eating pancakes off fused Spectrum dinnerware (capped with 100sfs) and running it through the dishwasher for years, with no signs of weathering. This doesn't surprise us, as ours is a very durable glass. But we can't recommend selling your S96 products as "dishwasher safe." Better safe than sorry: "Handwashing recommended."

	
	
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Q

We often slump or fuse Spectrum's non-System 96 iridescent glass. If the coating burns off, is it releasing anything dangerous into the atmosphere?

	
	
A

No. The metals that make up the coating are not really "burning off," they are absorbing into the glass and losing their color, becoming clear to the eye. Everything that can "burn off" has already done so, here at our factory, at initial application.

	
	
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Q

Should I be concerned about gasses or fumes coming off your glass while I'm fusing it in the kiln?

	
	
A

When Spectrum products are originally made, the raw materials are melted at temperatures that are around 1000 degrees higher than normal fuse temperatures. Any volatile components in the raw materials are driven off and captured in our baghouse during this process. Therefore, there no volatile gasses or particulate matters left to escape from the glass during the course of fusing.

	
	
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Q

What about your Fracture-Streamer sheet glass? Can we trust its compatibility? Bullseye issues a disclaimer on theirs.

	
	
A

All the components of System 96 Fracture-Streamer sheets are pre-tested prior to using them in production. The finished sheets are then tested in the same manner as all S96 products. So, yes. Our Fracture-Streamers are truly "Tested Compatible."

	
	
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Q

Why does devit occur along edges I have ground with a grinder?

	
	
A

Microscopically, you have "roughened" the ground area, creating thousands of tiny points from which crystal growth can easily propagate. Minimize grinding (not difficult with an easy-to-cut glass) or apply a light coat of overglaze to ground areas.

	
	
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Q

I have heard that, all other things being equal, ground edges on Bullseye glass devit less than ground edges on Spectrum S96.

	
	
A

All other things are usually not equal. S96 is a lower temperature glass. It takes less time / heat for S96 products to reach a given viscosity than it does Bullseye. Therefore, at any given point in a firing cycle, the S96 glass has progressed further (or matured more) along the desired process path. For this reason, people accustomed to firing Bullseye often inadvertently overfire S96, then draw conclusions. With regard to tendency to devitrify on a ground edge, Bullseye and S96 are functional equivalents: at similar points in their relative firing cycles (i.e., at equivalent viscosities) there will be no discernible difference, assuming similar colors and glass types are being compared.

	
	
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Q

I have been told that, because of its lower COE, Bullseye is more "durable," that is, will have less tendency to "weather" and is less prone to chemical leaching.

	
	
A

C.O.E. is coincidentally related to glass durability; it is not by any means a cause-and-effect relationship. It happens that the kinds of ingredients that are needed to lower C.O.E. are also the kinds of ingredients that increase glass durability.

It is perfectly possible to formulate high C.O.E. glasses with high durability.

The coincidence of Pyrex, (about C.O.E. 40) being highly durable and Moretti (about C.O.E. 104) being measurably less so, is meaningful because of the extremely wide difference in their expansions (over 60 points!) Narrower ranges of difference (within, say, 20 points) are very unlikely to show any relationship between expansion and durability. One example is float glass, commonly around C.O.E. 86, but much less durable than Spectrum fusing products, nominally around C.O.E. 96.

So, what about the relationship between 90 and 96 fusing families? We expect there to be no measurable difference in durability of these glasses. Being familiar with both formulas, there is no reason to believe that either glass would weather better or worse than the other.

	
	
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Q

I have been working with hot glass for many years, always using Bullseye. Recently, I needed to slump pieces 42-inches long. I decided to try System 96 because of the long sheet requirements. The project required slumping over a long "half-round" style mold. I used the same firing schedule I've always used for Bullseye.

The glass actually outgrew (sagged beyond) the bottom edge of the mold and was full of random tiny cracks. What is happening?

	
	
A

Two things are happening, both common occurrences when Bullseye users first try System 96. Bullseye requires higher temperatures and longer firing times than does System 96, to achieve similar results. In slumping, System 96 moves sooner and moves faster. So your Bullseye schedule is too hot and too long – thus the "over slump."

The higher heat needed for Bullseye actually caused your System 96 to stick to the mold – that's what caused the cracking. It is quite common for Bullseye users to have problems with their kilnwash sticking to System 96, for the same reason. You simply don't have to fire as hot with System 96. Going too hot for too long is unnecessary, causes problems, and of course takes more time and energy.

	
	
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Q

I'm having problems trapping unwanted air bubbles.

	
	
A

Air bubbles are trapped between layers of fused glass when the edges of the layers seal before the air has escaped. It is a common characteristic of kilnformed glass projects.  A number of techniques can be employed to reduce trapped air:

1.	Slow down your heating process after you reach 1050° F (566°C). Proceed slowly through the slumping temperatures up to 1250°. The increased time allows more air to escape from between the glass layers before the edges seal it in. 
2.	Create natural avenues of escape by using smaller pieces in your design. Every intersection of glass pieces is a natural vent for trapped air. A larger piece of glass can be split for venting purposes, yet still appear as one piece in the final, fired project (assuming full fuse temperatures). 
3.	Place a "lift" between two layers to create a vent. A tiny scrap of clear (or color similar to project) glass can be placed at the project edge, between two layers, lifting the upper layer to allow air to escape. The "lift" should be invisible in the final, fired project.


	
	
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Q

Why am I having trouble with the kiln wash sticking to my piece?

	
	
A

More than likely, your firing temperature is too hot. Try experimenting with your fuse cycle. Either go to a higher temperature for a shorter amount of time or try a lower temperature for a longer period of time. This is a common problem with fusers accustomed to working with Bullseye, which requires hotter, longer firings than System 96.

	
	
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Q

How can I prevent bubbles from forming between the kiln shelf and the bottom layer of glass?

	
	
A

This problem is gas. Small amounts of moisture in the kiln shelf or shelf primer may be turning to steam at high temperatures. Or, some organic material (dirt, filings or other debris) are burning and gassing off at fusing temperatures. First, try using firing paper between the shelf-primer and the glass. This product is air-permeable and will allow more air to escape than direct-shelf contact.

Next, try increasing the time spent around 250°F (hold it there for, say, 1/2 hour). By this point, the moisture has turned to vapor. Holding the temperature there for a brief period will allow this vapor time to find it's natural avenue of escape.

If you still have a problem, there is probably some chemical reaction taking place between the kiln shelf and the shelf primer. The reaction, which will be occurring at higher temperatures (1100 – 1300°F) is giving off a gas, which is creating the offending bubble. Solution? Again, first try taking it slower between 1100 and 1300°F. Spend an hour making that ramp. If that doesn't work, then try

a. a different shelf primer
b. a new batch of your existing shelf primer
c. a new kiln shelf, preferable made of a different material

	
	
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Q

I am re-melting Spectrum glass and using it for blowing. Is there any danger from breathing the fumes?

	
	
A

It depends on when you choose to breathe the fumes! During the re-heating process, at temperatures of 2450-2500°F (required to re-melt our glass), there will be some measurable "gassing-off" of volatile materials. Commonly, this gas is directed from your furnace or melting chamber up and out a flue designed for this purpose. At these temperatures, if you hold your face over the flue (or the molten glass) and breathe deeply, you are in danger of both ingesting some nasty stuff and burning your face off.

However, this does not normally present any danger to the hot shop, since, as stated, fumes created during melting should not be directed into the studio.

Most studios blowing glass, casting glass or otherwise forming re-melted Spectrum glass are most concerned with fumes they might encounter at forming temperatures, typically in the vicinity of 2100°F. There will be no measurable gassing-off of ingredients at forming temperatures. At higher temperatures (lower viscosities) materials volatilize that at lower temperatures (higher viscosities) remain inert. Think of water: at boiling temperatures steam is produced. Steam is not produced at lower temperatures, though the material is still very hot.

Also, once hot glass is exposed to air (at forming), a surface "skin" is immediately created that adds another layer of protection against any gassing.

	
	
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Q

I'm having some trouble with orange glass turning red when its fired, or red glass becoming darker or more opaque.

	
	
A

Some color chemistries are inherently less stable than others. Reds and Oranges in particular are "striking" colors – the more time they spend at high temperatures, the more their color will "develop." Some "striking colors" are more sensitive than others, and some production runs of a glass will be more or less sensitive than other runs of the same glass. Here are some things you can do:

1.	Test! Simple testing will tell you what, if any, color shift to expect from any glass. When you know what to expect, you can't go wrong. (See discussion on  <http://www.system96.com/Pages/Sys96Questions.html#Anchor-35882> testing in Common Questions.)
2.	Use the striking characteristics to your benefit. If you have some red glass, for example, that you have learned will strike darker, you could choose to save that glass for lower-temperature projects. Or, plan your project to take advantage of the deeper red color created by the striking process.
3.	Limit the time your project spends at its highest temperatures. Many experienced kilncrafters favor the "Quick Cool" or "Flash Vent." Once your project has reached the state or stage you desire, turn off the power, open the kiln (8 seconds for fusing, 3 seconds for slumping) then close. Keep the door closed for a couple of minutes, then flash again. Repeat until 1050°F is reached. Then close the kiln and anneal. This simple process vents high heat and effectively "freezes" your project at the state you have chosen. And, by immediately cooling after your project has reached the state you desire, you minimize color change due to striking.

	
	
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Q

I have seen color streaks in some of your solid opal colors. Sometimes they disappear when I fuse, sometimes they don't. Should I be doing anything different?

	
	
A

We make every effort to keep these streaks to a minimum. They are areas of slightly darker color or slightly higher density, a common problem in opal glasses that is more noticeable in our flatter, smoother glass sheets. We think we can eventually learn to prevent the problem altogether, but for now, the easy answer is to turn the sheet over. The streaks are generally only on one side of the glass sheet.

	
	
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Q

Why is some of the Spectrum System 96 glass "rougher" at the edges than in the middle? Are these roll marks? Will these marks "fuse out"?

	
	
A

During forming, some of our glass runs colder at the edges than in the middle. The texture you see is simply the result of this chilling. At full fuse temperatures, this texture will smooth out. Here are some other options:

1.	Put the "rougher" side down in your project; allowing it to pick up the kiln shelf texture and effectively disappear.
2.	Trim away the areas you don't want to use in one project and save them for use in another.

	
	
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Q

I am seeing what looks like devitrification on the edges of some of my projects. I thought your glass wouldn't devitrify.

	
	
A

Spectrum System 96 products are devit resistant, not devit-proof. Comparative testing has shown spectrum System 96 glasses to be less prone to devitrify than other "tested compatible" products. Virtually any glass will devitrify if held long enough below its liquidous temperature. The edges are usually the most sensitive areas, because they are "cut" exposed, not shielded by the natural "skin" of the glass. For similar reasons, crafters cutting with a bandsaw have more edge-devit problems than those who score & break, and those who grind their edges with a grinder are still more likely to experience edge-devit. This has nothing to do with COE or glass type.

1.	Experiment with your time-temperature relationships. Devit is easily avoided with System 96.
2.	Consider using a light coat of overglaze on the edges, if that seems like a better solution. We recommend Fusion Headquarter’s "Fuse Master Super Spray." It has been tested extensively on Spectrum products and has also been approved for food bearing surfaces by meeting the American Ceramics Association standards for leachable lead.

	
	
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Q

What about the famous Borax overglaze you used to recommend?

	
	
A

The Borax overglaze is simple, cheap and gets excellent results. BUT, it will not stand weathering. Exposed to outdoor conditions or moisture (like repeated washings) it will eventually lose its shiny surface. The formulation and instructions can be found  <http://www.system96.com/Pages/Borax.html> here.

	
	
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New to 96?

What to Expect if You're Used to "90 COE?"


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If you're used to using “90” glasses, note that our recommended temperature curves are slightly different. For most projects you can use the identical firing cycle for System 96 as you would use for the same project made with a “90” COE product, and see little or no differences in the result. Test, and make adjustments as you like.

See also:  <http://www.system96.com/Pages/WhySystem96.html> "Why System 96"

 

			
	
© 2004 Spectrum Glass Company, Inc. PO Box 646 Woodinville, WA 98072 USA Phone: 425-483-6699 Fax: 425-483-9007 E-mail:  <mailto:%20Hotglass at System96.com> Hotglass@ System 96.com

All rights reserved. Spectrum, Waterglass, Artíque and System 96 are registered trademarks of Spectrum Glass Company, Inc. Baroque is a trademark of Spectrum Glass Company.

	
			


Tony Patti
  
 <http://www.glassblower.info> www.glassblower.info
  
 <mailto:gaffer at glassblower.info> gaffer at glassblower.info

 <http://www.glassblower.info/qr-code.html> QR Code for Tony Patti - www.glassblower.info

 

 

 

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