Ms. Nomers, the next generation

The cooling blanket or pot of vermiculite completely anneal my beads.

Uh, sorry, but, NO they don’t. These are methods of slowly cooling your beads to room temperature, but neither of these methods will anneal your glass.

The process of annealing is the removal of strain. The only way that annealing can be done is to hold glass at a temperature where the glass is in a state there the molecules can move but the glass itself has become very stiff. This is called the “annealing point”. It is a different temperature for different types of glass. For example, common Moretti anneals at about 960 F, and borosilicate glass anneals at 1050 F.

 The glass needs to hold at this temperature for a period of time to allow the glass molecules inside the piece to realign. Depending on the size of the piece and how many pieces are in the kiln, this time period can range  from 30 minutes to 3 hours. The longer the piece is held at the annealing temperature, the more in alignment the glass molecules become. In precision optics, it is common to do a procedure called ‘fine annealing’ where the glass is held at the annealing temperature for several days. Large telescope mirrors are annealed for months at a time.

One the annealing time has expired, the next step is to lower the temperature to the strain point. This is where the molecules of glass actually stop moving. It is fairly common to hold the kiln at the strain point for several minutes, this allows the kiln temperature to “catch up” to the controller. Then the kiln can be lowered down to about 500 degrees over several hours and shut off.

Beads that are not properly annealed will have stress in them, and at some point in time will fracture and break.

Cooling blanket and vermiculite pots are fine for slowling cooling beads, but they should be batch annealed as soon as possible, and certainly before they are sold.


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