QUESTION w/ Poll: Quicker annealing cycles

[Silver Moon Lampwork]

After I'm done torching I press the Anneal Now button and walk away. I don't watch it or worry about it at all. I think I've been using this kiln for about 7 years and nothing has ever gone wrong.

[FosterFire]

I have been using a digital controller for about 14 years. I don't worry about, I just set it and forget it, but I made sure to buy a well known brand by a reputable company. I have an Arrow Springs AF99.

[Lorraine Chandler]

Most of the annealing schedules are for glass as it sits, with different schedules for thicknesses.

Then there is the kind of glass which the elite group of lampworkers do which is usually much more involved.

Larger beads with murrini, stringer, frits, layers upon layers of different glass and colors and leafs and foils, kiln striking etc. etc. So annealing actually becomes a fine art in itself learned through trial and error and you will eventually learn different programs and how to reprogram your kiln all of the time.

It can take years to get really comfortable with lampworking as a whole.

Long conservative annealing schedules are your best friend

I have my kiln where I can look out my patio window and see the readout on the kiln in the studio window.

[Lorraine Chandler]

Originally Posted by Roaming

Now I am a bit confused. I batch anneal using a brick lined kiln (Paragon). My understanding was that after the hour long soak, you could just let the kiln shut off and cool down on its own. This is what I have been doing with no problems so far, but it has only been about a month since my first batch.

From reading the posts above, some say it may be cooling to fast and could result in breakage later on. I was wondering what the general consensus is about this. Should I change the schedule to slow down the cooling or just leave it as is?

.

Here is an article taken from Arrow Springs which they kindly put up on their website for all to learn from. Please consider purchasing one of their books they have on learning all about glass if you are a beginner and do not yet understand glass properties. It will make a world of difference for you.
What Is Annealing? Why Is It Important?
And How To Do It.

The following is an excerpt from our annealer manuals.

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 to something. The glass will also need to cool down a 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 temperatures 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.

The annealing temperature we recommend for Effetre (Moretti), Bullseye and Lauscha glasses, is around 940º F. Use around 1050º F for borosilicate glass. Around 890º F for Satake. Using a temperature controller can maintain the temperature to within a couple of degrees. Manual control using an infinite control switch can not 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 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 point in temperature at which any stress that develops below that temperature in the glass through the cooling process is only temporary. Stress that develops in the glass above the strain point 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. If you use a temperature well below the strain point of all the glasses you use to cool slowly down to before then increasing the cooling rate, you will not need to know the exact strain point temperature of each individual glass. Use 750º F for Satake and 800º F for every thing else.

The process to anneal glass once it is at the annealing temperature is as follows: 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, one hour. For a large paperweight, it can take half a day. Very large glass castings weighing hundreds of pounds can even take months. 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 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 above described procedure is very easily accomplished using a temperature controller that is programmed properly. 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 very fast. For medium to large beads, or small hollow sculptures, instead turn the infinite control switch to Low. This setting will make it so that the temperature loss is slowed down. After about fifteen minutes the oven temperature will have dropped to below the strain point temperature. Because as the temperature in an oven gets lower, its heat loss slows, and the glass temperature is below the strain point temperature, you can turn off the oven and let it cool to room temperature for the size of the items described here. You should slowly cool to a lower temperature before turning off the oven for large items. To cool even slower, put the infinite control switch to a setting of 2, then after the temperature drops a 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 what any of those glasses will distort at. 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 and 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.

[Dragonharper]

Depends on what I'm doing. Mostly I garage and anneal. The only cycles I may cheat on are the strike and the final cool down, once the glass is below the strain point.

[28676bhe]

Does doing both count? I keep my beads in a manual kiln long enough to kindasorta anneal them I then batch anneal in a different kiln later at more exacting temperatures.

I know this may sound crazy, but as a fuser who has several kilns, I just couldn't justify spending $800 for one that was limited (pretty much) to one thing.

I really like my setup better than any I've seen in a professional studio, too!

Barbara

[PittsGlass]

Barbara,

Doing both definitely counts. You gave it a soak and generally slow cool in the first kiln, and a detailed annealing cycle in the second. As long as you are not having losses due to the faster cool in the first kiln, you should be fine. Why buy more stuff if what you have is working for you.

[Kayo222]

Well, I voted for daily annealing.....I don't torch daily, but I go through the whole slow cycle every time I do. But like others have said, I fill the kiln,too. It doesn't bother me to set the controller and go do other things....I have built a sense of trust with my kiln. This may be good OR bad....

[Dr Bill]

bye

[GabiLoraine]

Lorraine thank you so much for posting all of that information!!!