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Boiling Glass?

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grammy
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Boiling Glass?

Postby grammy » Wed Dec 23, 2015 11:37 am

I have seen several references on You Tube about boiling glass. It is where you put a layer of glass down, then bubble powder, then two more layers of glass. Take it to 1700 and and the bubbles rise and mix the glass. My thought is that it does not exactly "boil" is that so? I was wondering if anyone has done this and how were the results. I want to put french vanilla on the bottom and then some amber and another color. Trying to make what may look like rocks or stones.

Merry Christmas.

Emily Speight
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Re: Boiling Glass?

Postby Emily Speight » Wed Dec 23, 2015 1:42 pm

You are right, it doesn't actually boil.

It also has been giving mixed results... and not all are good.

I haven't done it, but supposedly you can do it with baking soda or borax (I can't recall the exact formula) if you don't have the bubble powder.

JestersBaubles
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Re: Boiling Glass?

Postby JestersBaubles » Wed Dec 23, 2015 4:38 pm

I did it with baking soda once. I didn't like the results. Not my thing :)

Dana W.

tob
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Re: Boiling Glass?

Postby tob » Fri Dec 25, 2015 6:03 am

When trapped between fused layers of glass the powder releases gas which creates the bubbles. In the case of baking soda - sodium bicarbonate - the bubbles would contain CO2. Baking soda will also change (raise) the COE of the glass immediately in contact with it, by adding sodium. So it would be wise not to go too wild with it.

Although I don't know the composition of the "bubble powder" you mentioned, it is likely to act in a similar manner - both creating bubbles and affecting the COE of the glass in the immediate area.

Morganica
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Re: Boiling Glass?

Postby Morganica » Sun Dec 27, 2015 6:35 pm

I think you're mixing up a couple of processes. When I've heard the term "boiling the glass" it's meant deliberate overfiring, i.e., using an extremely hot or prolonged processing schedule that makes the glass very liquid/soft/loose/runny. Liquidish, runny glass will seek its own level in a stack of glass, and produce some really interesting patterns and colors. It's sort of like a pot melt that stayed in the pot...on steroids.

When you have different fusing glass formulations--IOW different colors of glass, different coatings such as dichro or irid, different opacities of glass--they often have different viscosities, specific gravities, hardnesses, etc. As long as you keep the glass relatively cool in a normal fusing schedule, it doesn't move much and so it pretty much stays where you put it.

Overfire that glass, by raising the processing temp to, say, 1650F and holding it there for a couple of hours, and everything starts moving around. The really soft glasses such as black will go first, soften, rise or sink depending on the glasses that surround them. Metallic coatings (dichro/irid) will lift off the surface and float to the top. Trapped air will try to rise and join with more air, forming bigger and bigger bubbles that rise to the surface, carrying glass from the lower levels. By the time the hardest glasses (usually the whites) are soft and moving, everything has started to seek its own level.

Once it cools it looks very much like sugar when you're boiling it to make candy, hence "boiled" glass. But it also tends to change the glass chemically so that some colors, especially the warm ones, can become incompatible or extra prone to devit. Boiled glass is gorgeous stuff, but you have to be a bit careful using it with regular fusing glass.

Bubble-making (for me, anyway) is a different process. I use bicarb (or a couple other powders) to produce controlled placement of bubbles within the glass. I put a very tiny dot of baking soda where you want the bubbles to originate, then cap and fire as normal. A tiny bit produces a BUNCH of bubbles, and it's easy to over do it. I typically mix up a solution of baking soda and water and paint it in the spot, then let it dry before I cap it. By diluting it I have a little more control.

The only difficulty with that method is you really have to control the firing schedule. If you fire too hot or too long, the glass gets soft, the bubbles coalesce and rise, and you lose them. I was trying to figure out how to incorporate nice, medium-sized bubbles into one part of a transparent casting while leaving the rest of the cast perfectly clear, and it was a lot trickier than it looked--it pretty much required two separate castings to get right.

I suppose you could combine those processes, i.e., paint the bottom glass layer with bicarb to promote LOTS of bubbles and increase the tendency of the bubbles to carry glass up through the layers while boiling the glass. That would increase the mixing effect in the final product. I'm not sure it would add enough to make it worth the additional pitting and trapped gas you'd get in the glass. Might be interesting to try it.
Cynthia Morgan
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JestersBaubles
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Re: Boiling Glass?

Postby JestersBaubles » Mon Dec 28, 2015 9:47 pm

Here is one of the boiled glass tutorials, which uses bubble powder or baking soda:

http://www.twolassesglassclasses.com/Documents/High-Fire_Kiln_Work.pdf

Dana W.

Lynn Perry
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Re: Boiling Glass?

Postby Lynn Perry » Thu Dec 31, 2015 1:12 pm

JestersBaubles wrote:Here is one of the boiled glass tutorials, which uses bubble powder or baking soda:

http://www.twolassesglassclasses.com/Documents/High-Fire_Kiln_Work.pdf

Dana W.



Thanks for the link, Dana.
Lynn Perry

Valerie Adams
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Re: Boiling Glass?

Postby Valerie Adams » Fri Jan 01, 2016 12:54 am

I think it's important to note that the instructions posted above say to anneal Bullseye at 950°, which at that thickness (four layers) is incorrect. Bullseye lowered their annealing recommendation to 900° for thicker pieces. The one-hour anneal is also far too short for a four layer piece.

Emily Speight
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Re: Boiling Glass?

Postby Emily Speight » Sun Jan 03, 2016 8:15 pm

This is the web page that I think is originating a lot of questions:

http://www.glass-fusing-made-easy.com/b ... glass.html

tob
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Re: Boiling Glass?

Postby tob » Thu Feb 25, 2016 9:10 pm

Valerie Adams wrote:I think it's important to note that the instructions posted above say to anneal Bullseye at 950°, which at that thickness (four layers) is incorrect. Bullseye lowered their annealing recommendation to 900° for thicker pieces. The one-hour anneal is also far too short for a four layer piece.


Annealing Bullseye at 960° (or 950) is not "incorrect", per se. It is just that several years ago the people at Bullseye discovered that the annealing time of thick pieces can be shortened by soaking at 900F instead of the 960 they previously recommended. 960° still works fine. It just requires a longer ramp down time for thick pieces. Here's where their tech article about it can be found - http://www.bullseyeglass.com/methods-id ... glass.html

Nor is the 1 hour annealing soak time "far too short" for the 12mm (1/2") thick piece mentioned in that article - 4 layers of 3mm each. For that thickness Bullseye currently recommends a 2 hour soak at 900F. Since the annealing temperature used for this piece was 960F, one hour should be just about right because the stress will be relieved faster at the higher temperature.

This is a pretty good example of how annealing happens within a range of temperatures, not just at a single point. Bullseye's old annealing schedules that used 960F as the annealing soak temperature worked fine in the past - and still do. But their newer schedule allows for a shorter overall time when taking into account the required ramp down to below the strain point, which is why they changed their annealing recommendations in 2009.


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