Trash to Treasure
W. J. Wheeler
Glass Technician
University of Wisconsin
Madison, Wisconsin

Once the desired cut mark or scribe has been made, the bottle is set up to rotate, and the torch activated. Adjust the National hand torch for a short, small, hot flame, reducing the fuel and oxygen until the flame barely stays lighted. The purpose is to stress the glass along a narrow area around the circumference of the bottle. While the bottle is rotating, apply the flame tangentially at the point of the scribed cut mark. I count "one thousand, two thousand, etc. up to seven or eight thousand", holding the flame steady, then, remove the flame and the crack develops. In some instances, the neck just jumps off, and you can catch it. If the neck doesn't release after cracking, push the neck towards the body of the bottle, then pull the neck off. Pushing it together generally completes the cracking all around. Nothing new here, it is standard procedure for cracking large diameter soft glass tubing.

(At this point, you have invested a nickel of deposit in raw materials, if the cut is not satisfactory, trash it, you have not lost much. After all, there was the thrill of emptying the bottle. When it works, you are on your way to making something worth two dollars…where else can you turn a nickel into two dollars?) …… Author

THE FIRE POLISHING OPERATION

Center the cut end of the cut glass, while rotating, and apply heat with a gas only yellow flame, taking care that the gas doesn't "chimney" into the interior of the glass. Blackening from the carbon in the flame develops on the glass as it is heated. Gradually increase the heat of the flame by adding oxygen, until you can see the black carbon being burnt off. Keep adding oxygen until a strong, hot, blue flame is produced, about 5 inches long, applying the flame tangentially to the rotating glass surface. Maintain heating until the edges roll, and a bead develops equally around the circumference of the glass. Reduce the amount of oxygen at that point, and heat gently back about 3/4 inch from the open end. If there is some blackening of the ceramic decal at this point, decrease the gas and increase the oxygen amounts to your flame, producing a sharp, hissing flame. The lead in the paint of the decal will then be oxidized and cleaned up. It doesn't take much heating at this time to bring up the decal almost to its original color. When cool, the black is usually completely gone. Heat off with a gentle, gas only flame for 15-20 seconds, and stop the rotation and remove the glass from the machine.

Obviously, heating one portion of the open end of the glass produces a temperature gradient from molten to room temperature. Along this gradient, strains are developed that, in time, will be severe enough to cause cracking around the circumference of the glass. These strains can be removed by raising the entire glass assembly to a temperature near the glass softening point, and allowing it to cool evenly, resulting in relieving the stresses. Oven annealing at this point, raising the glass temperature to over 470 degrees and allowing it to cool slowly will remove all stresses induced by violent heating. The oven is the best choice, and if one is seriously producing these glasses should look into buying an oven capable of reaching this temperature, for instance , a ceramic kiln. Batches of cut glasses then can be inserted in the oven, raised to the annealing temperature and cooled slowly.

There is a scheme used when I produce novelties, whereby I take the heated glass, and using two 3 pound coffee cans, place the hot glass in one, and pour "Vermiculite" over the hot glass, covering it completely. This material is used as packing material for shipping chemicals, and is also used as a soil amendment by nurseries. The "Vermiculite" is a good insulator, and allows the glass to retain its heat longer, resulting in most strain being relieved. It will take several minutes to cool to room temperature, as opposed to a minute or so in air. The dust on the cooled surface can be removed with a paint brush or rag.

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