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Tips, Techniques, and Questions -- Technical questions or tips |
2006-07-22, 2:58pm
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More ideas than talent
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Join Date: Sep 17, 2005
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But annealed beads don't look any different....
We tested a friend's old scientific kiln yesterday.
I sacrificed some wonky beads for the experiment and they survived just fine. So the question is: Since they don't suddenly have a sign on them saysing "Hey we've been annealed", are there any indicators to look for that would show whether everything happened in the the way it was supposed to?
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Wendy
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2006-07-22, 5:27pm
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I've read of some (negative) color changes happening during annealing for beads with reactive metals in the glass, but other than that.. not that I know of.
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2006-07-22, 5:31pm
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Pyromaniac
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I believe you can check glass beads for stress using polarized lenses. The glass without the stress would be annealed.
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2006-07-22, 6:36pm
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More ideas than talent
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Do polarised sunglasses count?
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Wendy
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2006-07-23, 4:04pm
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Pyromaniac
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Somehow, I doubt it.
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2006-07-23, 4:36pm
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You need a polariscope. If memory serves me, it's two polarized lenses placed at 90 degrees to each other. You put your object in the middle (with a light source) and can see the stress that way. I think the object needs to be transparent, too-or something like that.
And as far as I know, yes, polarized sunglass lenses would work. Look up "polariscope" and I bet you'll find what you are after
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I've got way cool handmade bags for sale in the Garage Sale area for a buck each!
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2006-07-23, 8:32pm
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More ideas than talent
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Join Date: Sep 17, 2005
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We pulled out a polarising lense filter for a camera and held that up to a light source and didn't see anythng much in the unnanealed or annealed beads.
However now that I have seen a picture of a polariscope might be worth another try in a slightly different configuration.
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Wendy
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2006-07-24, 2:50am
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More ideas than talent
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Quote:
Originally Posted by LampworkbyLori
I've read of some (negative) color changes happening during annealing for beads with reactive metals in the glass, but other than that.. not that I know of.
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Ha ha - with a hot head I get those reactions up front!
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Wendy
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2006-07-24, 5:23am
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ManBearPig
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Polariscopes only work on clear glass, or transparents with very little color.
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2006-07-24, 5:33am
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Pyromaniac
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I was in a hurry before, but my answer about polarized sunglasses is correct... Even if the lenses are the correct type, you would have to disassemble the glasses to utilize them as a polariscope. If I recall correctly, Arrow Springs offers a polarizing stress scope for under $50.00, and yes, the glass must be at least somewhat transparent.
I believe you can also buy plastic polarizing filters in sheets relatively cheaply, if you can find them. I know McMow Art Glass has them in stock at their store in Lake Worth, FL for approximately $20.00.
Some Reference material on glass strain: http://www.public.asu.edu/~aomdw/GSI/Glass_Strain.html
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2006-07-24, 7:16am
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ManBearPig
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You can get polarizing filters at your local photography store. I got a pair of them for $3 a while back.
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2006-07-24, 4:56pm
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I stand corrected! This is very interesting.
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2006-07-24, 9:43pm
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Gentleman of Leisure
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Annealing is something you have to take a little bit on faith...
IF you know properties of glass and take it to the known annealing temperatures for a reasonable amount of time, you have to trust that the process has happened, and there is no visual indicators process has happened... You have to trust the "science"..
Dale
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2006-07-24, 11:07pm
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sorcerer
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I use a polariscope every day in the normal course of my glass practice. I have built several for friends, you need 2 linear polorising filters (photographic shop )
you need to mount them one above the other with about 50mm ( 2 inches ) between them, you need a small light source beneeth the lower one. turn on the light source and rotate the upper filter untill you cut off as much of the transmitted light as possible when viewed down through both filters. A clear piece of glass with stress when placed between these filters and viewed from above will exhibit a halo effect in the glass. If you make a clear glass ball about 20mm in diameter on the end of a rod, cool it in vermiculite, and place it between the filters you will see a perfect example of stress. This ball should then go into your kiln with your beads to anneal, after which you should check it again, if it has annealed properly there will be no halo. The first of these images is unannealed, the second has been annealed at 480 Deg C for 10 mins.
Bernard
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2006-07-25, 1:00am
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Entropy increasing....
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Oh that's trippy.
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2006-07-25, 3:15am
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I'm a lilac!
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Quote:
Originally Posted by castaway
I use a polariscope every day in the normal course of my glass practice. I have built several for friends, you need 2 linear polorising filters (photographic shop )
you need to mount them one above the other with about 50mm ( 2 inches ) between them, you need a small light source beneeth the lower one. turn on the light source and rotate the upper filter untill you cut off as much of the transmitted light as possible when viewed down through both filters. A clear piece of glass with stress when placed between these filters and viewed from above will exhibit a halo effect in the glass. If you make a clear glass ball about 20mm in diameter on the end of a rod, cool it in vermiculite, and place it between the filters you will see a perfect example of stress. This ball should then go into your kiln with your beads to anneal, after which you should check it again, if it has annealed properly there will be no halo. The first of these images is unannealed, the second has been annealed at 480 Deg C for 10 mins.
Bernard
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Soooo cool Bernard! Thanks for posting those pics!
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2006-07-25, 4:19am
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More ideas than talent
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Join Date: Sep 17, 2005
Location: Melbourne, Oz
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Quote:
Originally Posted by Dale M.
Annealing is something you have to take a little bit on faith...
IF you know properties of glass and take it to the known annealing temperatures for a reasonable amount of time, you have to trust that the process has happened, and there is no visual indicators process has happened... You have to trust the "science"..
Dale
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I trust the science - I want to know if I can trust the kiln!
I'm also curious about how much stress is in the unnanealed beads given that most of my beads are pretty small anyway.
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Wendy
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2006-07-25, 4:32am
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More ideas than talent
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Join Date: Sep 17, 2005
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Quote:
Originally Posted by castaway
I use a polariscope every day in the normal course of my glass practice. I have built several for friends, you need 2 linear polorising filters (photographic shop )
you need to mount them one above the other with about 50mm ( 2 inches ) between them, you need a small light source beneeth the lower one. turn on the light source and rotate the upper filter untill you cut off as much of the transmitted light as possible when viewed down through both filters. A clear piece of glass with stress when placed between these filters and viewed from above will exhibit a halo effect in the glass. If you make a clear glass ball about 20mm in diameter on the end of a rod, cool it in vermiculite, and place it between the filters you will see a perfect example of stress. This ball should then go into your kiln with your beads to anneal, after which you should check it again, if it has annealed properly there will be no halo. The first of these images is unannealed, the second has been annealed at 480 Deg C for 10 mins.
Bernard
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Thanks Bernard. That shows it really well. The only other photo I had was in a Warm Glass book and it wasn't even in focus.
I'm hoping that's whetted hubby's interest enough to make me one as a side project when he's in at the studio tomorrow...
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Wendy
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2006-07-25, 9:23am
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Gentleman of Leisure
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Quote:
Originally Posted by wendbill
I trust the science - I want to know if I can trust the kiln!
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You do simple temperature test on kiln... Place a rod of glass, a couple inches long on two supports (one at each end)... Then take kiln up to annealing point (968 deg. F.) for Effetre and if rod does NOT sag, you are probably good temperature wise or kiln is at least running "cool", then take kiln up beyond annealing point, say to 1100/1200 degs f. if rod sags then kiln is reaching proper temperatures.... Its just simply calibrating the kiln (pyrometer) to test temperatures it achieves...
Dale
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2006-07-25, 9:12pm
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More ideas than talent
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Something else to try this weekend!
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Wendy
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