Mike Frantz:Long-Overdue Question

[Emiko]

Did anyone ask you this?
Why does it say that annealing tempreture is 470 C (870 F) at the Effetre web site? (I remember Lucio said that he anneals at below 900 F.) Or, should I ask why has it been 920-968 F in the US? If the manufacturer recommends 870 F, who dicided it to be 920-968 and why? Did anyone in the US scientificcaly test it?

Also what is the softening point? Most US vendors say it's 1050 F but I think I heard that it was around 1200 F when I started lampworking, and there are some web sites (of people who have been in the business for a long time) that support my memory. Has it been changed at some point in the last 10 years? I didn't find the information on your web site. (I'm asking you this because I recently fused gold decal onto two beads in the same color and same size in two different kilns at 1140 F for 25 minutes and one of them got a flat spot on the back and the other didn't. I wonder which pyrometer is correct.) Probably different colors soften at different temperature. The color I used was transparent medium Aqua.

[JetAge Studio]

Not Frantz here... but..Interesting... do you have a link to Effetre for that annealing info? (Google gives too many other websites).
Thanks,
Renee
JetAge Studio

[Emiko]

http://www.effetre.com/Immagini/murano/bacchetta/bacchette.pdf
It's their catalog in PDF and it's in Italian. Look at the top left corner of the page 3. "Temperatura di ricottura" means annealing temperature. If you use one of the online translation functions, recottura is translated as "re-cooking".

[castaway]

Here in Australia we have been annealing Effetre at 480C and wondering why the Americans ran there kilns so high. 515C is fine for Spectrum and Bullseye but too high for the Italian glass
Annealing is a function of viscosity, the softer the glass the lower the annealing temp, get yourself a polariscope and do some testing, 480C for 10 mins is fine for beads made from Italian glass and you can test this yourself.
cheers, Bernard

[Emiko]

I talked with Craig of Arrow Springs.
He said glass can be annealed at the straining point or higher temperature so long as you don’t go too high to distort it. If the temperature is higher, the amount of time that takes to anneal is shorter. So theoretically Effetre can be annealed at 840 F which is the strain point. But what pyrometer reads has errors in the range of + or - 0.3 % of the real temperature even if it is not faluty. So when it says it is 840 F it could be 837.5 F and it doesn’t anneal because it is lower than the strain point. Also the strain point vary according to colors so 840 F is not a rigid figure. So what they do is to anneal at 50 F higher than the strain point to be safe. Then why do they give higher number than 890 F? That comes from the experience. When pieces go into the kiln the surface is hot but the core is cooled. So if the temperature of the kiln is cooler, the glass reaches too quickly to the strain point and it causes cracks. 940 F was the temperature that the most people had the least cracks. Also going higher to 940 F to 968 F range gives a benefit of Bullseye and Effetre being annealed toghther. So the safest and the most convenient range is listed as recommendation. But if you are making something large rather than beads it is better to use lower temperature because the weight of the glass can cause distortion even under the softening point.

[WildBird]

Wow.
Thanks for the great information. For me it really helps to have the 'big' picture so I can understand the sub-information.

WildBird

[Toni Lutman]

I talked with Craig of Arrow Springs.
He said glass can be annealed at the straining point or higher temperature so long as you don’t go too high to distort it. If the temperature is higher, the amount of time that takes to anneal is shorter. So theoretically Effetre can be annealed at 840 F which is the strain point. But what pyrometer reads has errors in the range of + or - 0.3 % of the real temperature even if it is not faluty. So when it says it is 840 F it could be 837.5 F and it doesn’t anneal because it is lower than the strain point. Also the strain point vary according to colors so 840 F is not a rigid figure. So what they do is to anneal at 50 F higher than the strain point to be safe. Then why do they give higher number than 890 F? That comes from the experience. When pieces go into the kiln the surface is hot but the core is cooled. So if the temperature of the kiln is cooler, the glass reaches too quickly to the strain point and it causes cracks. 940 F was the temperature that the most people had the least cracks. Also going higher to 940 F to 968 F range gives a benefit of Bullseye and Effetre being annealed toghther. So the safest and the most convenient range is listed as recommendation. But if you are making something large rather than beads it is better to use lower temperature because the weight of the glass can cause distortion even under the softening point.

Great information Emiko! Thanks for passing it along!

[Judi_B]

Thank you Emiko. Good information to have. I hadn't thought about the thermal cracking problems at lower annealing temperatures. You might want to put this info in the "Tips" room with annealing in the title to make it easy to find in the future.

[Julz]

Nice detective work Emiko. Doomo!

[Emiko]

Hi Julz! Genki?

I posted this info in the Tips forum so that more people can read it, but this original thread is getting more traffic.http://planetsmilies.net/happy-smiley-584.gif

[Julz]

Hai! Genki desu! Anata wa?

Thank you for putting this in the tips section. It really does clarify the differences in scientific reasons, and actual use. I had never thought of it this way.

It's getting traffic because of the title!

[Sarabella]

Hai!
Important information! Thanks Emiko for finding and posting it!
Sals

[Hayley]

Emiko -

Thank you for the info! Did Craig say how much longer one should anneal as the temperature goes down? Say if you anneal at 960 for an hour, do you anneal at 910 for two hours?

[BeadMaven]

Emiko -

Thank you for the info! Did Craig say how much longer one should anneal as the temperature goes down? Say if you anneal at 960 for an hour, do you anneal at 910 for two hours?

Great thread!

I hope we get an answer to your question.
I lowered my annealing temp from 960 to 940 for my Terra beads.
I then doubled the soak time to 2 hours instead of 1.
I hope that was what I should do.

Help please :)

[Emiko]

I don't think you have to lengthen the soak time as long as you are annealing within the recommended range. I think Craig has left for the Sonoma bead show, so I'll ask him about annealing at lower temp than the recommended annealing range when I see him at the show this weekend.

[Karen Leonardo]

I have been annealing mine at 860 for years with beads not any bigger than 2 inches and have had no problems when flame annealed well. Got the temp from Ron at Art Glass House when I got my digital kiln from him. My flowers do well too. I always wondered why everyone used the higher temp myself Emiko....now we have the secrets :) Thanks.

Karen

[Hayley]

Karen,

How long do you anneal at 860 for?

Kimberly posted on Squid's Van Gogh frustration thread that you can lower the temp but need to anneal longer.

It would be great to get some guideline - I would love to anneal lower than my current 930 coz Terra still striking a bit in the kiln.

[Emiko]

Craig’s answer is....(regarding annealing at lower temp than the recommended range)
If you want to be really scientific, caliculate it using Jim Kirvin’s, Bandhu’s or whatever, taking other factors like thickness of glass or the tempreture of it before going in the kiln into consideration (and the pyrometer has to be reading the temperature correctly.) But if you see the equasions most people go http://planetsmilies.net/not-tagged-smiley-14790.gif
Add half an hour or one hour and if it doesn’t crack it’s good.
(not a quote. Something to the effect.)

[Hayley]

According to Bandhu's table - a 1/2-1" thick piece anneals at 968 and soak for 15 minutes, compared to a 1 1/4" thick piece anneals at 948 and soak for 23 minutes.

With that logic, I deduce that each 20 degrees require an addition 8 minutes of soak time.

I will check Kervin's book and compare.

[Sue H-K]

Thanks Emiko for finding and posting this info!