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Some hints to improve your glassworking skills
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As an instructor for many neon workshops, I've discovered some helpful tips to facilitate and improve your glasswork. Because literature on the subject of neon glassworking is quite rare, some of the tips I offer here are not covered in other publications. In lieu of formal training, many neon fabricators learn by trial and error. Unfortunately, this leads to incorrect techniques that become ingrained. This month, I offer some practical hints to help beginners and old-timers alike.
Setting the fires
Previously, I mentioned that a scientific glassblowing expert once told me, "A good fire is half of a glassbender's work quality." Assuming that you use the correct torch tip for the type of gas you're burning, and the gas and air pressure are adequate, how do you determine the correct setting for your fires? My first answer is a common scientist's response: "That depends." To be more precise, the correct fire setting depends on the type of glass you use.
The lead-glass fire
For decades, the U.S. neon industry used lead glass almost exclusively. Lead glass is named for one key ingredient: lead oxide. Today, lead glass contains 12-28% lead oxide by weight. When lead glass is heated in a flame containing unburnt fuel, oxygen atoms are released from this oxide to complete combustion of fuel in the flame. After the oxygen is consumed, metallic lead remains in the glass, forming a black-silver deposit. But when the flame itself contains sufficient oxygen to completely burn all combustible material, additional oxygen atoms from the tube's lead oxide are not consumed. In this case, the glass stays clean.
To work lead glass, therefore, the flame setting must contain enough air (oxygen) to allow complete fuel combustion. To set this type of flame, adjust your torch until you achieve a gently hissing, long, dark-violet flame with a small, bright-blue cone in the center (Fig. 1). This setting is right at the point where the air cannot be increased without causing the flame pilots to be unstable or flickering, thus extinguishing the main flame within a few seconds.
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