Annealing - What is it, and Why do it?

[arrowsprings]

Annealing - What is it, and Why do it?

Annealing is the process of making the entire glass item uniformly hot and holding that temperature steady long enough to remove all stress caused from the manufacturing process. The annealing cycle also includes cooling down slow enough so as to not allow too much stress to build back up.

When glass is held at a steady temperature over a length of time, it is called soaking. Soaking the glass at a higher temperature has the advantage requiring a shorter soaking time for the stress to dissipate, but also runs the danger of being so hot that it may distort under its own weight or of sticking. The glass will also need to cool down through a longer temperature range, and this will take longer than if it were annealed at a lower temperature. Soaking the glass at a lower temperature has the advantage of a shorter cooling time, but requires a longer soaking time to remove the stress, and, if soaked at too low a temperature, will not even remove the stress no matter how long soaked.

After the glass has soaked for the proper length of time, all of the manufacturing stress will dissipate, but stress will reappear during cooling. The faster the glass is cooled, the more the amount of stress the glass will acquire.

The annealing temperature for any glass is actually a range. The higher end of the range is a temperature set to be safely below any possible chance of distortion. The lower end of the range is a temperature high enough for heat soaking to be effective within a reasonable amount of time. The commonly used temperature for any particular glass is actually just a temperature chosen as a compromise between the higher and lower ends of the range, in other words, a temperature in about the middle of the range. An exact temperature is not what is important. What is important is that you keep the temperature steady for a period of time before slowly cooling the glass to room temperature.

We recommend the following annealing temperatures:

· Effetre (Moretti), Bullseye and Lauscha glasses - around 940º F.
· Borosilicate glass - around 1050º F for.
· Satake - around 890º F

Using a temperature controller can maintain the temperature to within a couple of degrees. Manual control using an infinite control switch cannot hold as tight a tolerance, but is adequate. This is one reason that we use annealing temperatures near the middle of the range.

As the glass cools, the outside will always cool faster than the inside. As glass cools it contracts. If the outside of the glass cools much faster than the inside, the outside glass contracts faster than the inside glass. This variance in contraction causes stress in glass. Too much stress and the glass breaks. The slower the glass is cooled, the less the amount of temperature variance throughout the glass and the less the amount of stress that will develop.

The cooling of glass is most important between the annealing temperature and the strain point. As explained, glass will develop stress in itself through the cooling process. The strain point is a temperature below which any stress that develops in the glass is only temporary, and above which it is permanent.

Once the glass has stabilized to room temperature, temporary stresses will disappear. Because of this fact, you can accelerate the cooling time below the strain point temperature and not worry about this strain causing the glass to break at some time in the future. However, cooling at too fast a cooling rate can still break the glass from thermal shock while still in the annealer. The strain point for glass varies between manufacturers and even between different colors from the same manufacturer.

Select a temperature well below the strain point for all the glasses to be annealed, and then slowly cool to this point. Once the selected temperature is reached you can safely increase the cooling rate. You will not need to know the exact strain point temperature of each individual glass.

Suggested strain point temperatures:

· Satake - Use 750º F
· Everything Else - use 800º F

The process to anneal glass once it is at the annealing temperature is as follows:

1. First soak it for a period long enough to remove its stress. For a small bead, this can be as little as twenty minutes. For large beads, use one hour. For a large paperweight, it can take half a day. Very large glass castings weighing hundreds of pounds can even take months.

2. After soaking, cool the glass down past the strain point temperature slow enough so as not to allow too much damaging stress to develop. For a small bead, this can be as fast as 600º F per hour (10º F per minute). For large beads, one-half or one-third that rate. A large paperweight may require a rate as slow as 50º F per hour (less than 1º F per minute). Once the glass temperature has past below the strain point temperature, the cooling rate can be increased without causing permanent stress in the glass. However, cooling the glass too fast below the strain point temperature can still cause the glass to break during cooling due to thermal shock.

The procedure described above is very easily accomplished using a properly programmed temperature controller. To do it manually using an infinite control switch and a pyrometer, you first soak the glass as already described above. After the soak time has elapsed, there are several options, depending upon the size of the glass being annealed. For small glass item, such as small beads, simply turn the infinite control switch to off. Since the annealer has been on for a while, the brick walls will have absorbed a lot of heat. This stored heat keeps the firing chamber from cooling to quickly.

For medium to large beads, or small hollow sculptures, instead turn the infinite control switch to Low. This setting will slow down the temperature loss. After about fifteen minutes the oven temperature will have dropped to below the strain point temperature. As the temperature in an oven gets lower, its heat loss slows. Once the temperature is below the strain point (for the size of the items described) you can turn off the oven and let it cool to room temperature.

For larger items, you should slowly cool to a lower temperature before turning off the oven. To cool even more slowly, put the infinite control switch to a setting of 2, then after the temperature drops to about half way to the strain point temperature, set it to Low.

When soaking and cooling different sizes of glass, use the rate that is best for the larger pieces. You cannot over soak or cool too slowly the smaller items.

You can anneal together borosilicate, Effetre (Moretti), Bullseye and Lauscha glasses. The temperature to use is 1000º F. It is a little high for all but the borosilicate, but at least 30º F below distortion temperature for any of these glasses. It is a little low for the borosilicate glass, but you can compensate for that by increasing the soaking time.

To find out more about specific soak times, cooling rates and how it relates primarily to glass thickness, consult one of the many excellent books available that cover the subject. Two very good books are: More Than You Ever Wanted To Know About Glass Beadmaking by James Kervin and Contemporary Lampworking - A Practical Guide to Shaping Glass in the Flame by Bandhu Scott Dunham.


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[Bob Torbett]

Being a newbie, I don't have a kiln as yet. I was shown a technique to fire anneal smaller beads in the torch before putting in the blanket. Is this a viable alternative or should I expect these beads to shatter?

Any help anyone can provide would be greatly appreaciated

Bob

[Kevan]

Originally Posted by rtorbett

Being a newbie, I don't have a kiln as yet. I was shown a technique to fire anneal smaller beads in the torch before putting in the blanket. Is this a viable alternative or should I expect these beads to shatter?

Any help anyone can provide would be greatly appreaciated

Bob

I have beads that are two years old that weren't annealed and they never have shattered. Even dropped them on the cement floor - no shattering.

My husband has read volumes on annealing glass. Scientific books on the subject as well as talked to many people about it. He insists it is not necessary for anything under 1/2 from the mandrel.

I've heard Jed at Frantz say it's not necessary either. However, we anneal our beads because everyone else does and we don't want to be the nail who's head sticks up.

[J. Savina]

Don't you just hate the wait of annealing? But good things come to those who wait. Annealing is very necessary, no matter what size the bead is. Any time you force molecules together with heat, annealing is the only way for it to bond without stress. Like a marriage, there is a bonding period necessary in order to be successful. Stress doesn't only come in the form of extreme temperature change, but also in the form of abrupt force, as in dropping or throwing on a cement floor. But I wouldn't test my beads that way. Even the smallest bead will succumb to stress if not annealed properly. Try taking a small un-annealled bead out from room temperature to 18 degrees below zero (like we get here in the midwest) . I don't test my beads that way either, but think about this. If your un-annealed beads were a part of a piece of jewelry, the unsuspecting jewelry wearer would not be too happy having their beads pop while just going outside in the extreme cold. Yep, I'm going to keep annealing, no matter what size the bead is.
For those of you that are just starting out, and don't have a kiln yet, I would suggest saving your pennies to get a kiln if you're serious about lampworking, or renting kiln time to batch anneal your beads. I don't care to batch anneal, but if you're careful about heating your beads at the proper rate, it can be successful.
J.

[Kevan]

Flame annealing small objects is quite sufficient from what I have been told.

That said, I kiln anneal my beads.

[Cosmo]

Flame annealing is not the same, no matter what the size. The reason is that there is no way to consistently control the temperature.

For small objects there just aren't as many stresses, so they don't break as often.

[Mr. Smiley]

Flame annealing is a MYTH. Plain and simple. You may be able to limit the amount of stress in a bead, so it doesn't shatter, but it's NOT annealed. I've done tons of research on annealing. Annealing isn't the process of heating the bead to the annealing point. It's cooling it, after a long enough soak, very very slowly. The ramp down should be no more than 100 degrees per hour for normal sized beads and slower (exponentially), the larger you go. For example... Josh Simpson has his megaplanets on a 30 DAY annealing cycle. You can't go too slow, but you can definitely go too fast on the ramp down.

[GinnyHampton]

Originally Posted by Mr. Smiley

Josh Simpson has his megaplanets on a 30 DAY annealing cycle. You can't go too slow, but you can definitely go too fast on the ramp down.

Seriously?!?! Wow . . . can you just imagine the anticipation! I can barely wait overnight

[Reenie]

Aren't the beads supposed to go directly into the kiln for annealing as soon as they are done?
It seems like from what I'm hearing you can wait and add all your beads at once. By then though, haven't they cooled? How do you make a bead and another and another...and keep putting them in?
Is this in any of the books out there? Yeah can you tell I'm lost?
Don't have the money for a kiln right now but have been trying to research them and what exactly they do.
Thanks for the topic
Irene

[motherbeads]

I would love to hear an answer to Irene's question. I've always had this same question about batch annealing. Anyone?

Renee

[pam]

Hi Renee, why didn't you answer the question? You know the answer as well as anyone. lol

Hi Irene, Batch annealing, of course, takes beads that are already cooled and heats them up very slowly to the annealing temp and then takes those beads through the whole annealing process back to room temp. Some beads survive, some don't. When you make beads and let them cool to room temp without annealing, stresses that are built up in the beadmaking process are not relieved and are still stored within the beads. These stresses may result in spontaneous cracking. This cracking can be all the way through the bead, just on the outside layers, or internal. When the cracks are on the outside or all the way through, then we don't bother to anneal them. When the cracks are internal we have no way of knowing that so we anneal them. Bringing the cold beads up to annealing temp puts stress on the beads, that's why we do it slowly, but some of those with internal cracks or higher amounts of stress will shatter from the heating and some won't. Those that don't will be fully annealed at the end of the annealing process, but those that have internal cracks will have a flaw that will cause that bead to be weaker than a bead with no internal cracks. Those beads when dropped or put in extreme conditions may crack. Beads that have been batch annealed with no internal cracks will be just as strong as those that have been annealed straight from the flame, but the problem is that you cannot tell which beads have internal cracks and which do not. So, the best method for annealing beads is to come straight from the flame to the heated kiln.

With regard to your second question,"How do you make a bead and another and another...and keep putting them in", you have your kiln set at the annealing temp and you open the bead door or lid of the kiln and put your finished bead inside. You make a second bead and slip that one inside the kiln also, being careful not to touch the first bead. You keep doing this until you have finished making beads for that session and then you start your annealing process. You hold your beads at the annealing temp for a period of time, then very slowly cool your beads at whatever speed you determine your beads need to be cooled.

I hope this helps.

[Cosmo]

I will add one thing...

Once the beads are at kiln temperature, it doesn't matter if they touch. When we do classes, we have beads piled on top of beads, and never have a problem with them sticking or deforming.

When I put one in that just came out of the flame, I put it in so it isn't touching anything. But, by the time the next one is ready to go in, the previous one is at kiln temp (which is below the softening point) and it can be moved and touch whatever else with no problem.

However, I wouldn't do this unless you have a digital controller and you know it is pretty accurate.

[Heather/Ericaceae]

The process of "flame-annealing" (I think of it as "flame-cooling") won't result is a properly annealed bead, but it is a useful INTERMEDIATE step for bead that you'll be batch-annealing in a kiln later on. I always try to even out the heat in my beads as much as possible before I stick 'em in the vermiculite can. Basically I heat a bead to an even but very low glow (not softened at all, just warm), then let it cool for 10 or 20 seconds (depending on the size) then flash in back into the flame to re-heat just the surface. It helps them survive until I can properly anneal them (which I pay $30 for every two months or so - I'm a slow beadmaker!) But it's not a replacement for kiln-annealing! And I look forward to the day when I can have a kiln at home so that I don't have the have the less-reliable can-cooling at all.

-Heather

[Ironmountain01]

I'm with Heather on this. As I do have a kiln but don't have the power to run it in my studio, I "flame anneal" before placing the bead in the dreadded fiber blanket. When the beads are all cool then I batch anneal. However I have to kiln-sit as I don't have a dig-con yet (grumble), but when I get one, at least I'll be prepared if (when) I have to send it in for repairs!!

[motherbeads]

Hiya, Pam! Well, I guess my concern is with the fact that you are bringing the beads to annealing temperature only. I always sort of wondered if that was enough to reduce the stress created in the glass by not annealing right after the bead is made. Does that make sense?

I don't even understand myself most days...

LOL,
Renee

[pam]

I understand what you mean, Renee, but as long as the bead is held at the annealing temp for a sufficient period of time to allow the bead to be the same temp all the way through, I don't think there is a problem with relieving stress. However, again, it won't heal the results of the stress from the first cooling. Rather than deal with it, I think it's much easier to anneal straight from the torch, of course that can only happen if you have access to a kiln.

[Kalera]

I've had "flame annealed" beads break more than ten years after being made. Funny thing; they're still in one piece, but they have a crack down one side. A lot of people can't tell, but I seem to have a special affinity for finding cracks in glass... I can "feel" them and they're plainly visible to me even when others can't see them until they're pointed out and viewed under bright light.

After I batch annealed all my old beads they stopped cracking. Haven't lost a single one, but I did recently find a box of my oldies that never got batch annealed and every single one of them has a hairline crack down one side.

You could tell me that means I wasn't "flame annealing" them properly, but then I would just laugh at you, and we can't have that, now can we?

[Kalera]

Oooh I lied... three of them aren't cracked yet. Ugly, but intact. I'd better batch anneal these babies before it's too late!

I was looking for my Murano beads that my friend brought back from Italy for me so I could take a pic that shows how all of them are cracked down one side, but I can't find them.

[Jerry]

So, if I don't anneal the beads I make I shouldn't do anything with them? Except maybe keep them in a box someplace safe from being handled and for sure don't sell them.

[Mr. Smiley]

For sure don't sell them.

If you batch anneal, you can releive all the stress in the glass by soaking at the proper annealing temp. At this temp, the glass molecules move freely enough to relax. When you cool them slowly enough, they don't push or pull against their molecular neighbors. they just all kind of chill together. Happy glass molecules make stronger beads... it's just that simple.

Pam was dead on about some unanealed beads having internal cracks that go undetected... there is no way to guarantee it's a perfectly good bead, unless you go from torch to kiln, unless it's transparent glass. Then you could probably see any internal problems. It's just good practice to go from torch to kiln. If it wasn't, we wouldn't be running our kilns all day. I know I'd save the power if I could.

[tabcaver]

HELP,...I want to anneal some beads, about 15 or so ranging in size from 1/2 inch to an inch. All are Moretti. I've read what Arrowsprings has posted but I need to know how slow of a ramp to use, how long to hold, how to cool (time range). I have a Rio Grande kiln, but the program ramp holds at a higher temp than what Arrowsprings recommends. Any thoughts???

[voic]

Hi, i was wondering if somebody can tell me how fast does a (let's say) 1 or 2" gather starts to cool down to room temperature (average temp) after is beeing made very hot and then pulled out of the flame. Or if u have your kiln already at the annealing temp how much time do you have to put the piece into the kiln?

And Brent,

For example... Josh Simpson has his megaplanets on a 30 DAY annealing cycle.

Are you referring to the 3.5" diameter megaplanets? Why do they have to stay so long in the kiln?

Thanks,

[voic]

Soory for the second question, i saw now some larger pieces, u must be refeering to them 9.5" , 18"