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Casting with Spruce Pine batch billets

For discussion of processes related to using Bullseye glass, including kilnforming and kilncasting, torchwork, blowing and stained glass.

Casting with Spruce Pine batch billets

Postby louis.copper » Mon Apr 01, 2019 10:14 am

Hello,

I tried to cast with glass made into billets from Spruce Pine batch. It turned out to be a mess ... lots of devitrification. I am trying to understand the whole thing better... but if this is not the place, fair enough. I was in desperation mode, asking everyone I could think of...

Lou Copper
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Re: Casting with Spruce Pine batch billets

Postby louis.copper » Tue Apr 02, 2019 8:32 am

Here is some further detail about the problem ...
- I used Spruce Pine batch with various oxide colorants to try my hand at my own colors
- I mixed small batches in crucibles for melting into glass in a high temperature kiln at 2150F.
- after the glass was formed, I moved the crucibles to another kiln, positioned to flow the glass into molds.
- after the glass was shaped, I compared results, and adjusted recipes to tweak the colors.
- after arriving at a couple pleasing colors, a larger batch was prepared, then added into an empty furnace, with a large crucible reservoir of about 120 lb capacity.
- once melted, this glass was ladled into a steel frame on a marver table, then transferred to an annealer.
- the two colors made, a yellow and a blue, both turned out beautifully at this stage.

These billets were then used to cast several shapes in large plaster/silica molds. Biggest, 10 " dia solid cast sphere, smallest 3 " cube. They were all fired together, and in order for the big spheres to be properly annealed, the whole cycle was necessarily slow, and there was a prolonged time about 1250F.. where devit can occur.
Some of the small cubes were not this glass, but were glass made deliberately for casting.. One was a Bullseye blue, which was one of the clearest of the resultant cast shapes.
The big spheres were badly devitrified... the outer surfaces of all the starting billet pieces were visible and clearly covered with devit that looked like thick flannel. In addition, in areas away from the edges and faces of the starting pieces, there were spherical burst-like growths of crystals scattered around. A mess, as I said.
In addition, there were an unusual number of large bubbles trapped against the surface of the mold wall, particularly at a level that seemed to be when the internally packed glass inside the sphere leveled off, and the reservoir glass flowed in on top of it..
Can anyone tell me:
-what is the fundamental difference between this glass and the glass made specifically for casting?
-I had hoped to make a whole array of my own colors, and then select certain ones to make for casting. Is this really not possible based on glass batch formulated for blowing? I am disappointed that if I make my own color this way there is nothing I can make with it by casting.
- is there any patch I can do to keep this process going? I am conducting tests to see if there is a heat work level that the glass can withstand (perhaps up to 1 " thickness, with fastest forming and annealing possible). Are there any additional additives I can blend in back at the batch stage (I mean here add to the already formulated Spruce Pine batch, since I am not making my own) that would have a chance to produce a workable casting glass?
Any comments or questions would be welcome, and might save me a ton of wasted effort in useless work. Thanks!
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Re: Casting with Spruce Pine batch billets

Postby marykaynitchie » Tue Apr 02, 2019 3:12 pm

People who work at Bullseye are very unlikely to have worked with Spruce Pine products ever, so you will need to depend on other members to offer advice.

We have worked with at least one artist who used our colored glass for hot casting into molds (Bertil Vallien), but this is a technique that we don't ordinarily practice, so we will hope that someone with more direct experience can help you.

Bullseye does offer glasses that are designed for kilncasting.

Mary Kay
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Bullseye Glass Co.

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Re: Casting with Spruce Pine batch billets

Postby louis.copper » Fri Apr 05, 2019 11:02 am

Hi Mary Kay
thanks for your response.
I was posting just hoping to find someone who understands glass more at a batch level. I want to learn from my experience, is all. I was in a kind of 'ask-everyone-I-can-think-of' mode because I have several hundred $ and tons of time invested, and don't quite get what happened.
Interestingly, in that same kiln run there was a casting of BE glass also, and it turned out to make one of the clearest castings in the load under the same conditions... but I'm not sure why that happened either.
I have been working with BE and other glass for a long time now. I was always under the impression for Bullseye that things like sheet scrap could be saved as useful casting raw material. But now it seems that glass with different end processing (like rolling into sheet) or end use may have been made with glass from a batch recipe made just for that one application.
Do you know if BE glass that I get as sheet comes from the same batch formula (other than colorants) that casting billet does? Excepting perhaps some additional bubbles from the form, will sheet glass cast in a similar way to billet?
As they are both made for reheating in a kiln, where temps are lower than for blowing but where times just above 1250 are longer, that they both may come from a glass batch designed to resist de-vitrification. Or perhaps they are similar but not identical?
I am a bit unclear about the Forum... is the intended discussion to focus only on bullseye glass and processing of it, or is it open to general glass questions? In the forum am I addressing BE employees and customers only?
I am sorry if I strayed from the prime directive of your Forum, or if I gave you heartburn some how.
Lou
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Re: Casting with Spruce Pine batch billets

Postby marykaynitchie » Fri Apr 12, 2019 2:08 pm

No worries--we try to reply to all of the questions for which we think we have good advice, and those tend to be questions about Bullseye products. Occasionally, people will have a question about Bullseye products, and we can't answer it, because it is being used in a different method than any we have tested.

I try to call out questions that we can't answer to encourage others who have different expertise to respond.

Our billets are made with the same formulas as the same style number of sheet glass. Our glasses are formulated for work in the kiln, unlike Spruce Pine Batch. We've been tinkering with them for a long time to make them work for casting.

Mary Kay
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Bullseye Glass Co.

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bit.ly/BullVideos
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