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Tips, Techniques, and Questions -- Technical questions or tips

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  #1  
Old 2015-02-20, 7:25am
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Default Annealing temp??

I keeps seeing posts about lowering the annealing temp in order to preserve the colors on striking glass. Now I am curious. What is the lowest you can go to safely and successfully anneal soft glass?
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  #2  
Old 2015-02-20, 10:13am
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Coe, brand, and color effect minimums.
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  #3  
Old 2015-02-20, 12:54pm
LarryC LarryC is offline
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Annealing generally occurs within a temp range and not a specific temperature.
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Old 2015-02-20, 2:25pm
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See "Contemporary Lampworking" by Bandhu Dunham. In the 3rd edition chapter 8 covers "annealing" along with charts for COE 104/32.
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Old 2015-02-23, 3:25am
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Annealing is the process of reducing internal stress in the glass during cooling.

If you anneal at the higher temp range for a given coe type the 'soak' time is reduced a great deal.
But that higher temp can change the way reactive and striking chemistry with in the glass works and will have an impact on the color once it is cooled to room temp.

You can also anneal at the lower end of the range for that coe but it greatly increases the amount of 'soak' time needed to relieve the internal stress and at the extreme low end can add several hours to the amount of time the glass has to stay at that lower 'soak' temp.

So its a trade off. How much time can you invest in annealing the glass and how much impact will annealing faster at a higher temp have on the chemistry of the striking color or reactive glass.

A lot of us anneal over night so time is not a very big deal. Learning to get the most out of striking colors and reactive glasses is pretty much a learned art form and unless you can encourage your 'inner OCD child' to come out and take exacting notes, it can take a few years to learn what specifically goes right when it works the way you want it to.

And then the manufacture runs into a shortage of the expensive chemicals that really makes your glass so gorgeous and has to change the formula and you have to relearn how to get it to do what it did so nicely with that batch you bought last year.



Now to answer the question you put forward; I do not know the minimum temperature soft glass wants for proper annealing nor do I know the time ratios for the highest and lowest temps. I think the number you are looking for is somewhere around 850 f but you might be looking at some 3 hours soak time per one quarter inch thickness in soft glass.

The odds are good that the places list above will have specific guidelines.

Me ? I like 920 for a half hour and then two hours down to 800 and an hour down to 700 and then I let it cool on its own overnight. ( I think. I set up the program on my kiln some three or four years ago and then I promptly forgot how I plugged in the numbers. I have it written in my notes at the back of the kiln manual if I really need it.)

Mostly I am still trying to get striking colors to strike at all so I have not had an issue yet with losing anything due to kiln temps. That will part of the learning curve in the next decade with the way I am figuring things out.
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Last edited by Speedslug; 2015-02-23 at 3:28am.
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  #6  
Old 2015-02-23, 7:21am
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Thank you all for your answers.
Speedslug came the closest to answering the actual question, but Alaska inspired me to dust of the "Contemporary Lampworking" books again and inspired some renewed creativity.
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  #7  
Old 2015-02-24, 1:44am
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There was a great discussion in 2008 about annealing cycles that I just found tonight and saved it in my favorites.

It is here : http://www.lampworketc.com/forums/sh...ad.php?t=83377

Seems that for soft glass the number is 860f. That is the point when the glass stops moving at all and what ever stress is still in the glass will be trapped in the glass until is warmed back above that. They called it the strain point temperature.

It is going to be slightly different for various colors and transparents versus opaques and probably from manufacturer to manufacturer. Most likely a plus or minus 5 or 10 degrees range.
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  #8  
Old 2015-02-24, 7:25am
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That's what I was curious about! Thank you so much for taking the time to look it up and share the information!!!!
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  #9  
Old 2015-02-25, 3:57pm
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Bullseye changed their annealing temp a while ago - here is there link:
http://www.bullseyeglass.com/what-sc...annealing.html
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