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So What is This “Annealing” Thing You Speak of?

August 3, 2008

 If you’ve looked at even a handful of lampwork bead listings on Ebay or Etsy, you’ve undoubtedly seem the term “annealed”. Most likely, the seller pointed out that their lampwork beads are annealed for strength. But what exactly does that mean, and why is that important? Aren’t we supposed to accept the fact that glass is fragile, and will break?

 

If you were to look up “anneal” in the dictionary, you would probably find two definitions, one very general: to strengthen or harden; and one more specific: to subject glass or metal to a process of heating and slow cooling in order to toughen and reduce brittleness.1

 

If glass beads are not annealed they can and do crack right down the middle of the bead. So what exactly does annealing do to prevent this?

 

Without getting too technical, the bonds that hold glass atoms together have different strengths.2 This is what allows glass to be gradually softened and worked with heat. Then, the bead must be cooled, or else we couldn’t use it! However, these temperature changes can introduce what we call stress in the bead. This stress is what causes the bead to crack.

 

Think of a bead like the inside of a hot pastry…it may be cool enough to touch, but when you bite into it, the temperature change is so great, you scald your mouth. The same thing happens when you allow a bead to cool at room temperature; the outside cools much faster, and those atoms start to re-form their bonds. However, the inside of the bead has a much hotter temperature, and these different rates of cooling means the atoms cannot properly re-aligned themselves into a stable structure throughout the bead.

 

Reputable lampworkers use a kiln to anneal their beads. When the beads are still quite hot, they are put into a hot kiln and allowed time to achieve an even temperature throughout the bead. Then, the kiln lowers the temperature very slowly, so there are no great disparities within the bead in terms of temperature. Some people use fiber blankets or warmed vermiculite to slow the cooling rate of their beads, but these methods do not allow the bead time to achieve a uniform temperature before they cool, and are not truly annealed.

 

Annealing isn’t an absolute guarantee against breakage—if the glass is not worked properly in the lampworking process and is allowed to get too cool while still being torched, stress can definitely enter the bead, and will not be repaired unless the bead itself is thoroughly reheated to a high temperature. However, properly created and annealed lampwork beads should last a lifetime.

 

1. American Heritage Dictionary

2. “Annealing Glass” Corning Museum of Glass, http://www.cmog.org/dynamic.aspx?id=5726

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2 Comments leave one →
  1. August 3, 2008 10:25 am

    Hello,

    I have found on youtube a nice visual explanation 😉

  2. Mallory permalink
    August 4, 2008 1:31 am

    Great article. You really know how to explain the bead making process.

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