Annealing temprature

[Havi]

Hello everybody,
At what temprature do you anneal your BE glass/

This sounds a beginner's question, but I am not a beginner...................
Years ago, the recommended annealing temp. was 516C

Then, BE advised thar 482C is Ok to use, and mostly this is what I have done...

The other day I read BE techsheet 4 , and found out that 516C was again the recommended annealing temp.


I wonder when did it change again, and why. What temp. do you use for annealing, and why??? And how would you proceed from there? Especially, would you stop again at 482C ? For how long. ?
Of course I am aware of different time should be used according to the thickness of the piece. But I would like to know what's happenning, and consequences of either.

Many thanks in advance
Havi

[Michael Stevens]

I anneal at 510 degrees usually just 1 hour for 6mm thick 12" in diameter. but my kiln also holds temperature for a long time so often if I just let it cool without adding anneal cycle it's ok. for thicker 2 hour anneal or longer I make sure to set it. I've had my kiln set at 500 and it's ok. 480 would be cool for my kiln and things crack if that low temp.

my controller won't allow a cool down and then anneal. so I have to set anneal cycle manually when lts at 510. it's a little annoying but I've learned to time it

[Brad Walker]

Bullseye's recommended annealing temperature was established at 960F/516C around 2000, then changed to 900F/482C about a decade later. As far as I know that's still their recommendation. (It's what's written in current versions of both Tech Notes 4 and Tip Sheet 4, as well as their Annealing Chart for Thick Slabs. I don't think there's a Tech Sheet 4.)

Historically, Bullseye's recommended annealing temperature hasn't always been a single number. Back in the late 1990's, they had 3 recommended temperatures, one for opaque glasses, one for transparents, and one for gold-containing glasses.

That hints at the answer to your question. Different glasses anneal at different temperatures. But rather than program seven or eight different annealing temperatures for seven or eight different glasses in a given piece, we just use a single number that's somewhere in the middle of the range and that should work for all the different glasses.

This lack of a specific number isn't as big as a deal as it may seem. All kilns are different, so 900F/482C in my kiln is not the same absolute temperature as 900F/482C in yours. And the annealing range is broad enough that you can hold at just about anywhere in the middle part of the range and still get good results. For most fusing applications the precise temperature isn't as important as the process of holding a while somewhere in the annealing zone (roughly 800 to 1000F/425 to 538C for Bullseye and Spectrum glass).

My belief -- Bullseye might not agree with me on this -- is that Bullseye changed the recommendation from 960 to 900F in order to save time when you're annealing thick pieces. For two layer or so pieces that are more typical, the time savings is negligible and it does not matter which number you use, or if you choose a random number between those two. My wife still uses 960F because she had her first and only annealing issue when she annealed at 900F. I use 900F if I'm programming the kiln or teaching a class and 960F if that number is in the controller from the time before when my wife used the kiln.

So my recommendation would be to use whatever reasonable number you want to use. The length of the hold is more important than the absolute number.

[Havi]

Thanks Michael and Brad,
Brad, I remember I read in one of your wife's books that she anneals at 516, and I asked you about it then.
Your answer was similar to the one you wrote here. Only this time it is even more detailed.

Usually I anneal at 482, but when firing something thicker, I anneal at 516, and then for a shorter while on 482.
However, I was so surprised to see a tipsheet by BE, realtively not too old, repeating this 516.
So
I thought perhaps something drastic had happenned, what do I know?

Very grateful for your detailed answer, yes, I am slow on annealing [broke too many pieces ,not to have learnt the lesson...]

stay safe, all fo you,
thanks again
Havi