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Eureka

This is the main board for discussing general techniques, tools, and processes for fusing, slumping, and related kiln-forming activities.

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Hugo Gavarini
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Postby Hugo Gavarini » Fri Mar 14, 2003 7:43 pm

My two cents,

In a past life, when I was involved with stainless steel (AISI 304 - AISI 316) recipients manufacturing, we had to use alumina grinder wheels instead of silicon carbide ones for this last contaminated the SS with carbon then lessening the inox properties.

Since irid is a thin metallic coating, commonly tin. Would it be possible a carbon-tin combination?. Is there a chemist-warmglasser here?.
Hugo

Steve Immerman
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Postby Steve Immerman » Fri Mar 14, 2003 8:36 pm

Hugo Gavarini wrote:
Since irid is a thin metallic coating, commonly tin. Would it be possible a carbon-tin combination?. Is there a chemist-warmglasser here?.


Hugo,

I had a similar thought. One of my test pieces consisted of taking a piece of NON iridized black and NON iridized clear, blasting the surfaces and then firing blasted side to blasted side. Got the same haze - which seems to me would eliminate a reaction with the irid coating as a factor.

Steve

Ron Coleman
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Postby Ron Coleman » Fri Mar 14, 2003 11:45 pm

Hugo Gavarini wrote:My two cents,

In a past life, when I was involved with stainless steel (AISI 304 - AISI 316) recipients manufacturing, we had to use alumina grinder wheels instead of silicon carbide ones for this last contaminated the SS with carbon then lessening the inox properties.

Since irid is a thin metallic coating, commonly tin. Would it be possible a carbon-tin combination?. Is there a chemist-warmglasser here?.


:idea: I think you are on to something Hugo. If carbon can contaminate stainless steel it is possible that it will contaminate the glass too.

Normally carbon would burn off in the kiln if the blasted surface was exposed to air, but in this application the blasted surfaces are sealed between the glass layers. There may be enough oxygen for the carbon to burn but no where for the gas to escape.

The haze may actually be microscopic bubbles of gas, CO2 gas.

A possible test would be to fire the glass open and hot enough to burn off the carbon but not melt the glass and then fire again to fuse the glass. Another idea is to clean the glass with an acid or something to dissolve the carbon. There was a post earlier in this discussion about surface cleaning.

See post by Mike Byers.

http://www.warmglass.com/phpBB/viewtopi ... c&start=15

Ron

Hugo Gavarini
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Postby Hugo Gavarini » Sat Mar 15, 2003 2:46 pm

Ron,

Your thesis has a lot of sense to me. In respect of cleaning, I believe it will be really difficult to eliminate all carbon particles because they may be actually incrusted into the glass surface, like thousand of minute bullets.

By the other side, it would be interesting to use this "problem" in favor of the artist. In fact, incrusting some particles on the glass surface "on purpose" would render interesting fusing results. Perhaps, a new field for experimentation.
Hugo

Kevin Midgley
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Postby Kevin Midgley » Sat Mar 15, 2003 2:49 pm

Maybe the silicon carbide is also the reason for scummy edges on pieces of glass that have been ground on a belt sander. Since devit needs a catalyst point to start the traces of carbon left behind might be enough to do it.

Jo Holt
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Postby Jo Holt » Sat Mar 15, 2003 6:34 pm

Steve Immerman wrote:
Hugo Gavarini wrote:
Since irid is a thin metallic coating, commonly tin. Would it be possible a carbon-tin combination?. Is there a chemist-warmglasser here?.


Hugo,

I had a similar thought. One of my test pieces consisted of taking a piece of NON iridized black and NON iridized clear, blasting the surfaces and then firing blasted side to blasted side. Got the same haze - which seems to me would eliminate a reaction with the irid coating as a factor.

Steve


Why does non-iridized black that has been blasted fire polish back to shiny black; but the blasted irid to irid fused together hazes :?: I took a class awhile ago where the irid to irid magnet I did hazed (I *thought* I cleaned it well with alcohol); yet the mica tile sandblasted with the same blaster fire polished beautifully. I believe the sandblaster had sc in it.

So many variables and I am so chemically challenged :(

Hugo Gavarini
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Postby Hugo Gavarini » Sat Mar 15, 2003 8:06 pm

Jo,

Your experience leads me to think Ron is on the track, because you had haze problems only when firing blasted side to blasted side.

Quote from Ron's post:

"Normally carbon would burn off in the kiln if the blasted surface was exposed to air, but in this application the blasted surfaces are sealed between the glass layers. There may be enough oxygen for the carbon to burn but no where for the gas to escape."

"The haze may actually be microscopic bubbles of gas, CO2 gas."

End quote.

Also Kevin, dealing with a different topic, suggested that:

"the silicon carbide is also the reason for scummy edges on pieces of glass that have been ground on a belt sander. Since devit needs a catalyst point to start the traces of carbon left behind might be enough to do it"

Either CO2 micro-bubbles or devit seems to have something to do with SiC (silicon carbide) blasting, sanding or grinding mediums. A microscope would be of use here, searching for bubbles after firing and for minute incrusted particles before. X100 magnification would be fine.

PS.: thank you Brad for the editing tool!.
Hugo

Jo Holt
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Postby Jo Holt » Sat Mar 15, 2003 9:49 pm

Hugo,

You explained it well; my apologies to Ron :oops: - I read the post but didn't retain it.

Kevin's comment on devit was enlightening, too.

If I'd known how much the science courses would apply to kilnwork, I would have tried a bit harder! :roll:

Thanks

Steve Immerman
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Postby Steve Immerman » Sat Mar 15, 2003 10:22 pm

Some observations:

When I first started using my blaster with silicon carbide, I noticed that the surface of certain colors of glass, particularly transparent purple, had many tiny pits on the surface. Small enough that you could only appreciate them from certain angles. From a distance it looked like a haze on the surface of the glass. You could only tell that they were pits with significant magnification.

Photographing these was difficult, but here are some photos taken looking through a 7 or 10x magnifier: the ruler shows millimeter marks.
Image

Image

I found that these pits were present to some degree, but almost invisible, on glass like opal black, opal red, french vanilla, and clear. A bit more visible on violet, and fairly visible on dark transparent purple.

I sent some samples to Tony Smith on which I blasted half, and he blasted the other half. Both sides appeared the same. If Tony used a finer grit, the pits were less noticeable and fewer, but still present. No matter how lightly I had the pressure in the blaster the appearance was the same.


Neither spray A, Super spray, Borax, or placing a clear cap prevented these pits from appearing on purple glass. With a clear cap, the pits just appeared beneath the clear, and actually seemed accentuated.

Cleaning with an ultrasonic toothbrush, Dawn, glass cleaner and alcohol before firing had no effect.

When firing blasted irid to blasted irid, the bubbles and haze appear right up to the edge where the top and bottom layer can be seen to come together. Looking closely with a magnifying glass, it sure looks like these pits are now tiny bubbles. I don't have a microscope handy. (and I try to stay out of that department at the hospital, Charlie.)

In pieces of irid to irid that have "chads" placed around the edge, the haze is just as noticeable.

When I switched the blaster grit from 120 Silicon carbide to 220 silicon carbide, the appearance of firepolished glass was somewhat better, but still had some pits. The irid to irid sandwich was worse.

When I switched to 120 aluminum oxide the pits and the haze seem to have magically disappeared.

As you can tell, this has been a problem that I've been trying working on since I got my blaster in November.

Empirically, I can see that using aluminum oxide seems to be the solution, but not sure why. Ron's and Hugo's theories have merit, but I don't know how to prove them one way or another.

My thought was that it had to do with the particle shape of the blasting medium, the type of fracture of the glass surface it caused, and some properties of the surface of glass that I don't understand......

Steve

Tony Smith
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Postby Tony Smith » Sat Mar 15, 2003 11:26 pm

The one thing that doesn't jive with Ron and Hugo's theories is that you and I both blasted on the surface of your dark purple glass and we both had haze. If Ron is right, any residual carbon should have been able to burn out. I think there's something else happening here, but unfortunately, I'm at a loss as to what that might be. Maybe the WarmGlass high power micrography lab can shed some light on this problem.

Tony
The tightrope between being strange and being creative is too narrow to walk without occasionally landing on both sides..." Scott Berkun

Ron Coleman
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Postby Ron Coleman » Sat Mar 15, 2003 11:29 pm

Very interesting findings Steve. Since the pits are showing up on the exposed surface it sure sounds like something is trapped in the blasting pits.

You mentioned you see this even on black opal which is one color I use a lot. For me, the black is a dream to fire after blasting with aluminum oxide. The surface always comes out looking like a million bucks.

I have a piece in the kiln this evening that is black opal with French Vanilla frit accents, before I fired it I blasted the black just to clean up a few small surface flaws and expect it to fire without problems.

Ron

Steve Immerman
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Postby Steve Immerman » Sun Mar 16, 2003 12:19 am

Ron Coleman wrote:Very interesting findings Steve. Since the pits are showing up on the exposed surface it sure sounds like something is trapped in the blasting pits.

You mentioned you see this even on black opal which is one color I use a lot. For me, the black is a dream to fire after blasting with aluminum oxide. The surface always comes out looking like a million bucks.

I have a piece in the kiln this evening that is black opal with French Vanilla frit accents, before I fired it I blasted the black just to clean up a few small surface flaws and expect it to fire without problems.

Ron


Ron,

I think that at times these pits are present, but are completely unnoticeable, and other times they are not there at all. I took soome of the magnets from last year that were blasted and firepolished by different people and looked at them with a magnifier. Although, with the naked eye they all looked fine, the surfaces were different when magnified. Some had no pits, and some had a fair number. Of course I don't know who used what kind of grit, and whether the grit was new or old etc. but it showed me that not all surfaces come out the same.

Steve

Hugo Gavarini
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Postby Hugo Gavarini » Sun Mar 16, 2003 2:51 am

Hello friends,

I have found this paragraph in a site which would be of use:

"What causes black bubbles in glass?"

"Bubbles with black insides are carbon or graphite. They would be from sawdust or small wood chips getting trapped in the hot glass. As they burned, a gas was released causing the bubble. When the glass cooled, the vapor condensed and deposited graphite (carbon) on the inside of the bubble."

From: http://www.insulators.com/general/glassfaq.htm
Hugo

Brian and Jenny Blanthorn
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Postby Brian and Jenny Blanthorn » Sun Mar 16, 2003 7:08 am

Hugo Gavarini wrote:Jo,

Your experience leads me to think Ron is on the track, because you had haze problems only when firing blasted side to blasted side.

Quote from Ron's post:

"Normally carbon would burn off in the kiln if the blasted surface was exposed to air, but in this application the blasted surfaces are sealed between the glass layers. There may be enough oxygen for the carbon to burn but no where for the gas to escape."

"The haze may actually be microscopic bubbles of gas, CO2 gas."

End quote.

Also Kevin, dealing with a different topic, suggested that:

"the silicon carbide is also the reason for scummy edges on pieces of glass that have been ground on a belt sander. Since devit needs a catalyst point to start the traces of carbon left behind might be enough to do it"

Either CO2 micro-bubbles or devit seems to have something to do with SiC (silicon carbide) blasting, sanding or grinding mediums. A microscope would be of use here, searching for bubbles after firing and for minute incrusted particles before. X100 magnification would be fine.

PS.: thank you Brad for the editing tool!.


Silicon carbide is very hard n sharp close in fact 2 diomond

So will pit more than aluminum

I think also it could B the silicon pushing the iridecent in2 the glass

Or binding with it in some way

I cant C carbon hanging arround at the temps discussed
Image

Steve Immerman
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Postby Steve Immerman » Sun Mar 16, 2003 11:00 am

Hugo Gavarini wrote:Hello friends,

I have found this paragraph in a site which would be of use:

"What causes black bubbles in glass?"



Hugo,

I'm sorry if my pathetic pictures give the impression that the bubbles are black. The photos are supposed to show the pits on the surface of the glass. The haze that appears between layers looks like tiny clear bubbles, but I couldn't get any kind of photograph at all that showed them.

Steve

Steve Immerman
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Postby Steve Immerman » Sun Mar 16, 2003 11:03 am

Brian and Jenny Blanthorn wrote:
I think also it could B the silicon pushing the iridecent in2 the glass

Or binding with it in some way

I cant C carbon hanging arround at the temps discussed


Brian,

I also tried blasting two pieces of NON iridized black and clear and fusing them face to face. Had the same hazy appearance.

Steve

Mary Kersey
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Postby Mary Kersey » Sun Mar 16, 2003 1:41 pm

I often sandblast a light "sprinkle" of coarse grit on the surface of layers of plate glass and fuse them together to trap the bubbles for an effervescent effect. These bubbles are much bigger than what you are describing but it certainly makes sense that the haze you are wittnessing can be trapped air bubbles from the pitting of the sanblast. And as Brian says the SC is considerabley sharper than AO and will give a different appearing "pit". It is harder and digs deeper perhaps leaving a different shaped pit as compared to AO. We use both types of grit to take advantage of their different cutting cappabilities and the different textures they create. Just my 2 cents
Mary Kersey

Hugo Gavarini
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What have we learned

Postby Hugo Gavarini » Mon Mar 17, 2003 10:46 am

Hello,

Thany you all for this terrific thread. I believe we have more doubts now, which is healthy. Doubt is better than ignorance, isn't it?.

So far, we positively know that Silicon Carbide produces some noticeable reaction on glass when fusing and that Aluminium Oxide does not.

We know that sandwiching blasted glass is more prone to get a haze finish when fusing, worst if blasting irid. But I have understood that even a single surface might show a haze of pitting when blasted with SiC.

We know that SiC have a high thermal resistance, without alteration well beyond fusing temperatures.

We know that it's very difficult to clean a blasted surface with cleaning agents only.

And, from the Craftweb board I learned that Silicon Carbide is very reactive with glass, so much as to be considered a colorant agent.

Finally, we know that we have to research a bit more. Possibly a X100 microscope would be of use.

That is what I have understood.
Hugo

Tony Smith
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Postby Tony Smith » Mon Mar 17, 2003 11:00 am

Hugo,

If you replace the word "reaction" with "effect" I would agree with most of your statement. It is not clear that there is a "reaction" occurring between the SiC and the glass, but there is certainly a different effect. Along the same lines, there is no evidence that the iridized surface has anything to do with the effect. Last evening, I sandblasted a clear piece of BE and fused it to a piece of black BE thereby sandwiching the blasted surface. As expected, I got the hazy appearance to the blasted section whereas the unblasted surface was not hazy.

I have sent my samples to Nikki for analysis under the microscope.

Tony
The tightrope between being strange and being creative is too narrow to walk without occasionally landing on both sides..." Scott Berkun

Hugo Gavarini
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Trying to isolate the culprit

Postby Hugo Gavarini » Mon Mar 17, 2003 2:28 pm

Hello;

There is something I remain doubtful (I am a stubborn man). Blasting with SiC irid or no irid surfaces, then sandwiching and firing will probably (or for sure) result in a haze appearance.

But what effect did you get when blasting with SiC a colored glass surface, then firing. I believe I have read Steve got a microscopic pitting effect under a magnifier and a slight haze when seeing with the naked eye. Am I right?. BTW, pictures by Steve are good ones, I misread them.

On the subject of “pittingâ€
Hugo


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