There are only a few basic bends used in forming glass tubing for neon use.
They are all performed somewhat similarly. To get started, cork the piece of tubing to be bent at one end, and connect the other end to your blowtube (see tools).
It helps to mark the glass with a grease pencil or similar to make sure you heat the right amount of glass, and at the place you want to.
To heat the glass with a crossfire, you both rotate the tubing to heat the entire diameter evenly, as well as work the section to be softened back and forth between the marks to heat it all. To heat glass with a ribbon burner, Adjust the flame length to be the same as the length of glass you want to heat, and then simply rotate the glass to be heated in position over the flame. Note that rotation is more important with a ribbon burner, since it only provides heat from one side.
The first is a simple angle or "L" bend, which can be a right angle or some other angle. It is done with the crossfire. The procedure is to heat about two tube diameters until the glass softens nicely, then in one smooth motion, bend the glass to the proper angle, blowing into the blowtube just enough to keep the glass from collapsing.
The next bend is the doubleback or "U" bend, which is used to hide electrodes behind visible neon, and similar purposes. It is also done with the crossfire. Heat about two and a half tube diameters until the glass begins to soften, then step down the rotation a bit and allow the glass to gather at the bottom of your intended bend -- this makes a little more glass available to stretch over the greater diameter at the bottom of the bend. Then quickly and smoothly bring the ends up parallel, pulling the bent section apart slightly to keep it from buckling, blowing into the blowtube enough to keep the glass at the correct diameter. Note that the bend is started first, then the tubing is reinflated to the proper shape.
The next bend is the drop bend, which is used to change levels in a design. Another crossfire bend, it needs about two and a half diameters of softened glass. After the glass is heated, the two ends are held parallel and one dropped down at the same as the two are pushed together slightly and the glass blown into to keep it from collapsing.
The next is a combination bend, which is essentially an angle bend and a drop bend all in one go. The glass is heated as for a drop bend, but when making the bend, one end is pivoted around the bend, and rotated 90 degrees at the same time, and as usual, air pressure keeps the glass from collapsing.
The next bend is the sweeping curve. This is the one done on the ribbon burner. The length of glass to be bent to the same curve is marked and the ribbon burner adjusted to that length. The glass is heated, with generous rotation, until it is soft enough to bend but still stiffer than for the tight bends above. Then the hot glass is lain on a pattern and bent to match. The pattern not only provides the bending path, but supports the glass so it does not sag until it cools.
These bends are all that are used in normal sign making. Neon artists, however, have different goals and often make up their own special techniques and bends to achieve various specific effects. Once the above bends have been learned, coming up with more is generally automatic for people with certain end results in mind.
The other major technique used in forming neon tubing is cutting and splicing. It is also the one that can't really be avoided. A really simple straight tube requires no bending at all, but electrodes still have to be attached to the ends, and this requires splicing skills.
Cutting glass tubing is a simple enough operation. Just score the place you want with a file on top, then briskly tap the bottom of the tube directly under your scratch mark, and with luck the tube will part neatly. This technique is one that gets a lot easier with practise. After you've made a hundred or so cuts (a day's worth of working with tubing will yield this), it will be nearly automatic. If a little burr of glass remains on the end you want to use, just grind it off with the file.
Splicing tubing is the trickiest part. To get ready, make sure the ends to be joined are clean and perpendicular. If you're splicing to tubing with a phosphor coating, remove a little of the phosphor (I use a finger protected by a scrap of cloth) so it won't interfere with the joint. Cork the far end of one tube and attach your blowhose to the far end of the other tube. Then, bring the two ends into the crossfire and rotate them in synchrony. When both ends are good and hot, bring them together with a little pressure, and then draw them back apart to even out the glass, continuing to rotate them together. Then, still rotating and heating, alternately suck and blow out the joint a few times to work the glass into itself and even out the joint. Then (still rotating), lift the joint out of the fire slowly, letting it cool gradually.
John Rehwinkel