Fire Polishing and annealing:

Fire polishing the ends of glass tubes and rods will seal small cracks in the end wall, reducing the chance of fracture originating from this source. Fire polishing the ends will also reduce cuts and abrasions or anything (corks, latex tubing, etc.) coming in contact with the glass end.

1. Cut 10 mm tubing into 16 inch lengths (or use tubing from previous lesson).

2. Light and adjust torch flame (sharp/soft).

3. Fire polish by rotating the glass tube end in the flame.

A good fire polish has a smooth finish, and the ID and OD of the glass tube remains unchanged.

 Tip: Hold the glass tube in a declining or horizontal position with the tube end protruded away from you. This will prevent the flame from traveling up the tube and out the far end, possibly resulting in a burn.

Annealing:

Whenever glass has been altered or shaped by exposure to a torch flame, you should  be sure that stresses have been introduced. The glassware you make can have some of the stresses reduced by hand annealing. Stresses are not usually visible to the naked eye, so you have to use a little imagination in performing this step. If you have access to a polariscope, check out your seals before and after annealing. The more complicated the seal, the more likely to have stresses harmful to the final product and you.

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