Neon: (Not Yet) the Lost Art
Times are changing fast, and ST always keeps up with trends. For illuminating channel letters, in most cases, neon remains the most economical choice regarding durability (useable lifetime) in outdoor conditions, initial price and energy efficiency. Even if some colors contain a small amount of mercury, neon is a “green” light source, because small amounts of energy, water and (renewable) natural resources are expended in its manufacture, compared to LEDs.
Correctly manufactured neon always has been a special art/craft. The “old guys” had their tips and tricks (today they’re called “knowledge” or “technology”), which are mostly lost now. But, I‘ll try to unveil a few tips to conserve the lore and pass it on to “the new kids on the neon block.”
How did neonbenders in the early 1920s properly process neon tubes without all the modern equipment – electronic gauges, turbo-molecular pumps, etc.? My simple answer: with experience and patience.
In today‘s world, only time is money, but the vacuum processing of neon tubes is still dictated by physical laws that demand time. Traditional neon processing began by evacuating the air (and water) for a few minutes, then backfilling with a few millibars of air to start the bombarding process.
After bombarding and evacuating the tube until it’s cool (which should take, at least, more than 15 minutes), the tube is backfilled with several millibars of “flushing gas,” a 75% neon, 25% helium mix, which is hard to acquire today (pure helium will do the trick). Then the tube is re-bombarded until the tube is hot again, then it’s evacuated to high vacuum until it’s cool. This “second” bombarding with a clean gas, rather than shop air, combined with another quarter hour for proper evacuation, vastly improves the tube quality.
Side-tubulating with a fully open tubulation (no restriction is made for a faster tipoff) also creates less vacuum-flow restriction compared to tubulated electrodes, with only a tiny free space between the glass and ceramic collar.
Another “old guy” trick: Gently heat the tubulation with a hand torch during the evacuation period after bombarding to remove impurities, which, if kept there, would be released into the tube during the tipoff, which would contaminate the tube.
The pace of today’s production has almost eliminated sufficient tube aging. Formerly, tubes were aged at least 24 hours at double the later operating current; the aging transformer was connected to a clock switch (45 minutes on, 15 off, every hour) to help even the distribution of the mercury.
Another “green” aspect, which has been discussed for a few years, is the use of mercury. LED salespeople often try to discredit neon as environmentally dangerous because of the use of mercury – without reason. OSHA tests proved the mercury contamination of workers and factory space in neon shops is much lower than in normal, electrical workrooms or stockrooms where CFLs and fluorescent lamps are stored or handled. However, workplace contamination can only be avoided by educated workers who handle mercury carefully.
Many neon suppliers have developed techniques that circumvent handling open mercury, but they haven’t gained remarkable marketshare because the material can be handled safely.
Neon tubes, as well as energy-saving lights and fluorescent lamps, must, and can be, completely recycled safely to recover all raw materials, contrary to LEDs. Several recycling systems and services are available. In Europe, a safe way to repair mercury tubing is widely used, but requires a large investment in a bakeout oven with special, exhaust, air filters.
Do-it yourself coloring
Matching colors in a partial sign repair is increasingly difficult because distributors no longer stock all the colors in all the diameters, nor do manufacturers always keep them in stock.
Because the average neon shop could never keep a stock of each glass color/diameter combination of coated glass, “do-it-yourself” coating was formerly quite common. So, only a set of clear glass in various diameters and a small jar of each color of the coating were stocked.
Two different coating principles are known. In the U.S., a special suspension coating of straight sticks doesn’t require oven baking, where the fluorescent material is mixed with a quickly evaporating solvent and an inorganic binder. The suspension is well stirred; the liquid is sucked up in the vertically mounted straight tube and drained, and the solvent is evaporated by a gentle puff of air. During draining, an (more or less) equal film of fluorescent powder is deposited on the glass wall.
In contrast, the dry powder, or “bead,” process was mainly used in Europe for larger-diameter tubing. Therefore, the glass is bent first, then a “glue” (comprising approximately 4% orthophosphoric acid and methanol) is distributed uniformly over the inner glass surface by shaking the moistened glass beads through them. The methanol is evaporated by warm air, which leaves a sticky, inner surface. A slightly excessive amount of dry, fluorescent powder is then poured into the tube and shaken so the powder sticks to every part of the glass wall. After the excess is poured out, a uniform coating remains, even in sharp bends.
The fluorescent materials for the “no bake” suspension process, as well as the dry coating powders, are almost impossible to buy today.
A third, “fake” method of coloring ready-made neon tubes was (and sometimes still is for large-scale production beer signs) commonly used in the 1980s. Standard, white-coated fluorescent tubing is bent and pumped as usual. The ready-made tube is coated on the outside with transparent/translucent paint. Once the paint dries, it’s hard to tell if it’s colored glass or not.
Tubes colored this way aren’t repairable, because the paint burns during bombarding. This paint is still available, but only in large, minimum quantities (20 gallons and up).
Because of electrical-code and regulation changes, especially the introduction of UL 2161, many “old style” magnetic sign transformers are no longer available. Thus, to repair old signs, it might be necessary to change the high-voltage wiring, because the mid-point ground must now be wired to a mid-point return, where the mid-point of the high-voltage circuit returns to the transformer. Otherwise, the mandatory safety circuit won’t work (or the transformer will shut down immediately).
Also, UL 2161 introduced strict requirements for electrical supplies, which created replacement problems in old signs. For example, at the transformer, a voltage/potential difference between ground and neutral must be lower than one or two volts, or the safety device will trip. Also, phase and neutral must never been reversed. In a worst-case scenario, this may require completely rewiring a building back to the main distribution panel.
On the other hand, with the introduction of UL 2161-style transformers, neon can be called one of the safest, sign-lighting principles. Neon-related fires occur infrequently. The safety device switches off the high voltage before anything severe happens. Thus, if a UL-2161 trans¬former keeps tripping, the installa¬tion is definitely faulty.
The size (or open-circuit voltage) of a neon transformer must be calculated (the transformer must be loaded properly) to avoid overheating or flickering. That requires stocking a full series of current and voltage (usually in 1kV steps) combinations. Even then, the loading, and thus, the brightness, of the channel letters in each circuit could vary visibly.
For this reason, an “adjustable” transformer was available for more than 60 years (in Europe). They open, core-and-coil transformers could be repaired, which was practically unnecessary. I’ve seen units removed from signs after more than 40 years of operation, with no sign of aging – and they’re still functional. Too bad it‘s no longer made.
Sometimes you can’t obtain the needed current/voltage combination, because manufacturers trimmed the product palette and suggest using a self-regulating, electronic power supply instead. But, in many applications, electronic power supplies can’t be used for environmental reasons, such as in outdoor installations or installations where the transformer has to be mounted a few feet away from the tubing.
Most neon-sign failures are caused by incorrect wiring on the high-voltage side, which results in insulation breakdown. Long runs of GTO, where water can enter the conduit, are most prone to fail. Today, you rarely see the old-style wiring method, where the transformer was placed inside the sign body or channel letter, and the tubes/housings are connected with bare, copper wire separated from the next surface by porcelain insu¬lator standoffs.
Together with glass and porcelain, air spaces form the best insulation in the long run. All plastic materials deteriorate with time, and ozone and water hasten the process. Only pure silicone rubber is an exception (and the only plastic material used in Europe for electrode boots/caps).
Another material the neon industry relied on for more than 90 years has practically disappeared: lead glass. Environmental activists caused politicians to enact laws (such as the European RoHS standard) that don’t permit some heavy metals and organic compounds – including lead -- to be used for electrical purposes. In the electronic industry, the regulation mainly focuses on tin-lead solder (which contains 35% lead), but, more or less accidentally, also includes lead glass.
Lead glass’s unique features can’t be replaced by other glass mixtures: the high electrical resistance; the easy metal sealing due to the chemical, oxygen-binding strength of the lead; and the very long temperature range of its working viscosity, combined with a high, thermal-shock resistance.
Many, big-lamp manufacturers tried to develop replacement glasses (such as the “lead-free lead glass” sold by an Italian company). I just received a request from one of the largest lamp manufacturers in the world to provide a source for lead glass, because its inhouse-developed replacement can’t be used for many small signal lamps and special stem seals.
Neon’s “chewing gum” bending behavior and its thermal-shock resistance create the tightly bent script letters you‘ll find only in lead glass. I would like to see enough demand for lead glass from the neon business so glass factories won’t phase it out completely. Then, the large neon suppliers will also return to using and selling lead glass. Why is it still OK to sell lead-crystal tableware and goblets, with up to 50% lead content, but not to use 18% lead glass for signs?
Many other glass-tubing beauties are missing. The really dark-red and perfectly clear Corning (or Schott) ruby red is sold by quarter sticks, if you can get a hold of them at all. Also missing are violet and brown-colored glass; black, opaque tubing used for permanent blockout sections; fluorescent glass (uranium yellow, Europium pink, etc.) or even candy-striped glass in rainbow colors.
Classic Neon Literature
Samuel C. Miller and Donald G. Fink: Neon Signs, McGraw-Hill, New York, 1935 (rare!)
Morgan Crook and Jacob Fishman: The Neon Engineers Notebook, 2nd Ed., Lightwriters Neon Inc., Northbrook IL, 2007 (ISBN 978-0-9716530-2-3)
Neon Lighting, International Assn. of Electrical Inspectors, Richardson TX, 2003 (ISBN 1-890659-23-1)