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Boro Room -- For Boro-related tips, techniques, and questions.

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  #1  
Old 2014-11-08, 9:29am
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Default Crackin as I type :/

So made a starry night last night with an opal inside. Garaged at 900, annealed at 1130ish for 2 hours then left to cool over night. Everything else made in that lot is fine.

This one however.
Before...

5 mins later it had the big top crack about ten mins after that a second one appeared....

And nope I didnt drop it didnt even set it down hard or anything like that....
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  #2  
Old 2014-11-08, 1:01pm
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Was it a gilson (gibson?) opal? They are compatible with boro. I wonder what went wrong.

Sue
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Old 2014-11-08, 5:04pm
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ya it's a gibson came from profound, so Im sure it is :/ I am wondering that too :/

Reworked it today its in the kiln again. See what happens the second time around.
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Old 2014-11-08, 7:50pm
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Before I knew the correct opal to use was Gibson, I brought some down to Playing With Fire and Ed was game to try it. The regular opal went pffftttt... and looked like a cloud of powder inside the boro. I don't remember for sure but I think it wound up being water dunked.

I've never tried the correct opal in boro. I've seen them though and they're beautiful.

Good luck with this next one.

Sue
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Old 2014-11-09, 9:26am
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why did you anneal at 1130? Way to high for certain colors. 1050 is more appropriate.
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  #6  
Old 2014-11-09, 11:47am
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Had some amber purple stuffs in there....
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  #7  
Old 2014-11-09, 12:23pm
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Quote:
Originally Posted by untamedrose View Post
Had some amber purple stuffs in there....
Anneal at 1050 and try to minimize the bubbles. Either one of those factors could cause problems.
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  #8  
Old 2014-11-11, 12:17pm
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The high annealing temp and long hold time are the issues. Never go over 1050 with anything with an opal in it, and don't garage it any longer than you have to.
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Old 2014-11-13, 12:54pm
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wait, so it's not a good idea to kiln strike something that contains an opal and a striking color?
hogwash, i do it all the time.
my guess is that somewhere surrounding that opal there was a bubble that wasn't "smooth". after i encase my opals and if there is any bubbles at all, i get the opal gather as hot as i dare in order to round out any bubbles.
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Old 2014-11-13, 1:01pm
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Quote:
Originally Posted by istandalone24/7 View Post
wait, so it's not a good idea to kiln strike something that contains an opal and a striking color?
hogwash, i do it all the time.
my guess is that somewhere surrounding that opal there was a bubble that wasn't "smooth". after i encase my opals and if there is any bubbles at all, i get the opal gather as hot as i dare in order to round out any bubbles.
You kiln strike for two hours? That is how long it was soaked at 1130. I dont think the opal had much to do with it. My supplier does suggest a higher temp anneal for the opals alone after encasing but I would not do that to most Boro color rod. As I said already one of those bubbles could also have been the culprit.
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  #11  
Old 2014-11-14, 7:21am
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where are you getting two hours? 25 minutes at 1125f is what i do. then down to 1050 for however long/thick the piece is.

2 hours at striking temps just might be problematic.
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Old 2014-11-14, 8:19am
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from original post

"Garaged at 900, annealed at 1130ish for 2 hours then left to cool over night"

Quote:
Originally Posted by istandalone24/7 View Post
where are you getting two hours? 25 minutes at 1125f is what i do. then down to 1050 for however long/thick the piece is.

2 hours at striking temps just might be problematic.
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Old 2014-11-14, 9:21am
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ah, i thought LarryC was referring to my reply, as that is the one he quoted.
carry on
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Old 2014-11-14, 9:46am
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Soaking at 1130 is not annealing. Boro is forgiving so maybe it gets misunderstood. Annealing occurs when the glass is brought through the strain point very slowly and evenly throughout. The strain point in boro is roughly between 800 and 950 degrees. Even though brick kilns cool slowly it is not necessarily slow enough. I am no expert on this, but this is how I learned it. I know there is lots of info out there on it for soft glass. The process is the same even if temps and glass is different. Sorry I can't provide a link. in my experience pieces with opals need to be well annealed and fully cooled to not crack.
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Old 2014-11-14, 12:55pm
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Annealing occurs before you go through the strain point. however, you can still thermal shock a piece if you take it too quickly through the strain point even after it has been annealed.
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Old 2014-11-14, 12:57pm
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annealing point is 1050. strain point is 950. this link explains it in depth http://www.glassalchemy.com/relieving_stress
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Old 2014-11-15, 6:38am
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The annealing process consists of two steps:
1: Reducing the stress in the glass from forming.
2: Slowly reducing the temperature below the strain point so that new stresses are not added. ( The strain point is the temperature at which any stress present in the glass, before cooling below the strain point, become permanent, until a subsequent annealing cycle is performed, and any stress introduced into the glass below the strain point temperature is temporary until the temperature in the glass equalizes.

The trick is to find a temperature, the annealing temperature, where the glass moves enough to equalize the stress forces built up during forming but does not move enough to deform. Typically for boro this is 1050 dF. Annealing can be accomplished at any temperature above the strain point but, the closer to the strain point the longer the glass needs to sit at that temperature. Some boro color has a nasty property of undergoing a COE shift when held above a certian temperature for a long time, that is why the manufacturer of the glass publishes garaging and annealing temps for each color.
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