Annealing

Compiled by Cathy Charles with special thanks to Joseph Walas, Bonni Harder and Deanna Dove for their kind contributions and assistance in the writing of this article.

It would seem that as beginners we would inevitably lose a few beads as we learn about the bead making process.  There are a few reasons that glass beads crack, break or just plain explode and while they may be as complex as incompatible glass, it could be as simple as the failure to remove stress areas from within the glass.

What is annealing?

Annealing is the process by which you remove the stress created when making your beads.  The annealing process, kindly defined by Joseph Walas, Glassblower for the East Carolina University Chemistry Department (and writer for American Scientific Glassblower’s Society), "involves a gradual and total heating of the glass object to the annealing temperature of the particular glass being used."

How to cool your beads

There are a number of different ways to cool (not necessarily anneal) your beads. The following are a few examples.

1. Wrapping your bead in a fiber blanket (placing between two layer or folded over piece,
2. Placing your bead in vermiculite (some suggest it has to be heated vermiculite and recommend crock pots),
3. Placing your hot bead straight into a kiln or
4. Flame annealing by bringing the bead slowly out of the heat (works on smaller beads).

The first two options do not remove the stress from the glass when it is worked in the flame and therefore they still need to be annealed. The last two options are reported to anneal beads although the last option is debatable, as it may not anneal your beads effectively.

 “While many people call the above technique flame annealing, please note that the above technique does not remove stress from the bead. In fact, as the bead cools--stress develops. Because the interior of the bead is hotter and more expanded, the exterior's rapid shrinkage places the interior under compression and thermal toughening. This method is useful for beads with consistent thickness and shapes because the stress produced would mirror the shape of the bead. A round bead would have a circle of stress which is harder to break…but a fish would not survive this method--a fin would cool more quickly than the body and there would be a stress line between fin and body, which would be easy to break.” Deanna Dove (http://www.mindspring.com/~griffindove)

Batch Annealing vs Immediate Kiln Annealing

Well renowned beaders firmly believe that cooling your beads in vermiculite or in a fibre blanket and then annealing later (referred to as “Batch Annealing”) is not as effective as placing a hot bead straight into a kiln at annealing temperature. The other side of the argument is that batch annealing makes no difference and is easier and a cheaper alternative to annealing your beads. So who is right? Both.

Perhaps this is a controversial response but the key issue is in the finishing of the bead. If the bead is heated evenly, from the core to the surface, and the temperature is brought down slowly, then batch annealing should be as effective as placing the bead immediately in a kiln at annealing temperature. The problem lies in achieving this process.

 “It does not matter whether or not the glass is in a cool or heated state at the beginning of the annealing cycle. What can be a factor to successful annealing is the speed or temperature ramp to the annealing point.” Joseph Walas, Glassblower for the East Carolina University Chemistry Department.

Bullseye Connection Instructor, Bonni Harder, believes the “real risk of batch annealing is breakage happening in the first cooling, or on the way up to temperature in the batch anneal firing.” If the bead cools too quickly, that is, the surface and core of the bead are different temperatures, then the bead has a high risk of cracking. It would be like taking a drinking glass straight from the freezer and putting it under boiling water … well that may be an extreme example but the principle is the same. Please don’t try that at home!

Bonni recommends her students use a kiln but understands this might not be a financial option for all beader initially.  For those without a kiln Bonni suggests “ the process of removing the bead from the mandrel can be enough to cause some beads to break before ever being batch annealed and would recommend leaving them on the mandrels until the firing is completed.”

Common Annealing Fallacies

There are a number of misconceptions about annealing and unfortunately they are thought to be truth. The four more common fallacies are:

1)      Annealing Strengthens a Bead

Annealing only reduces any stress in a bead that is the result of uneven cooling or heating.

2)      A longer annealing cycle will create a better bead.

“A conservative schedule for Moretti would be 30-45 minutes per inch at annealing temp, an hour ramping down to the strain point, another hour ramping down to room temperature. There are many variables such as the actual temperature of the kiln, how large it is, whether the bead is hollow or not, whether the bead has additional surface area or raised decorations, what glass is used--but in general beads are small enough to anneal rather quickly.” Deanna Dove.

3)      Annealing removes all the stress.

Interestingly enough all our glass garnishes like dichroic, silver, gold, reduction frit etc all create stress in our beads, which won’t be removed by annealing only reduced.

4)      Putting a bead in a kiln guarantees it is annealed.

As a general rule, if you are planning on selling your beads then you should anneal your beads. This is a stance that is strongly recommended by the vast majority of beaders and the International Society of Glass Beadmaker’s (ISGB) to uphold the image of high quality hand made glass beads in the industry.

June 2004     

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