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Neon Self-Training Part 4

Processing and lighting your neon tube.

By Randall Caba
Reprinted with permission from Sign Builder Illustrated

Finally, the moment you've waited for, assuming you actually waited: tube processing and lighting your neon tube. Yes, this is the mad-scientist and fun side of neon though some find it a little frightening.

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  • The Mad Scientist - You
    Tube processing is mad-scientist like because you work with high voltage electricity, high vacuum technology and gaseous elements that light in colors - neat stuff and the reason it's so Frankensteinien fun.

    But it's also scary because now you discover how worthy your work is. Will your tube hold a vacuum? Will it break under electro-mechanical, high vacuum and heat stress? Can you work safely and comfortably with high voltage electricity? Let's do some exploring and find out.

    First and foremost is safety. You're working with ten thousand to twenty thousand volts of electricity and pumping between one-quarter to one and one-quarter amps through the tube. That's enough juice to kill you and a horse.

    And you can cause permanent damage to tissues like your lungs and nervous system if you don't take the necessary precautions when working with high vacuum and liquid mercury.

    All possible safety concerns are beyond the scope of this article. So, you heard it here and you heard it now: Follow All Manufacturers' Safety Precautions when using their equipment or product! And if you don't understand something, research it first. The risks to you are that great.

    Generic Tube Processing Step-by-Step
    The following method of tube processing should be considered broad in scope and generic. It uses the simplest of equipment and the most basic technique. It assumes you understand pumping theory, equipment and material safety and use.

    1) Attach the neon unit to the manifold. The manifold will provide the passage for removal of impurities inside the unit and passage for pure inert gas to fill it. If you're using argon in the unit, make certain you attach a mercury trap containing a drop of mercury between the unit and manifold.

    2) Insert mica between tight bends. The electrical voltage used to bombard a tube is powerful enough to blow clean through your work. Mica will add electrical resistance and discourage blow through.

    3) Connect the bombarding transformer leads to each electrode and attach a temperature indicator to the tube.

    4) Open the vacuum valve and reduce pressure in the tube. Use of a vacuum gauge is recommended but a minimalist's alternative is to pump the unit for a few minutes then measure using simple butyl gauge a couple millimeters air into the unit.

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    5) Activate the bombarding transformer; the tube should light. If a leak is present, search for it using a spark coil and repair. Assuming no leaks are present, slowly increase current flow according the electrode manufacturer's suggestions.

    6) When the tube dims or flickers, make a pass with the vacuum valve as needed to keep the tube lit. A vacuum gauge is a better indicator of when and how much vacuum to apply.

    7) Maintain balance between vacuum and electrical current until the tube reaches a temperature around four hundred twenty-five degrees Fahrenheit, about the burning point of dry paper.

    8) Next, process the electrodes according to manufacturer's instructions. This usually involves increasing both current and level of vacuum. This operation heats the electrode shell to cherry red and converts a protective chemical coating.

    9) Once the electrodes are processed, allow the vacuum pump time to remove hot impure gasses, usually a few minutes or so. A quick check to see if the tube is ready to fill with inert gas is to close the vacuum valve then "bump" the bombarding switch. The tube should not light, as no remaining gases are present. If it does light, chances are good a leak exists in the tube or in the pumping system.

    10) If the tube is comfortable to touch, it's probably cool enough to fill with inert gas. Avoid filling too hot a tube as it results in low final pressure, cool gas exerts less pressure than hot gas. Use a chart to determine the appropriate fill pressure then add the correct gas, most often neon or argon.

    11) Once filled, "bump" the bombarding switch once again and check for proper color. Neon should light brilliant red-orange and argon dim lavender.

    12) Now safely remove all mica, wires and indicators from the tube. If filled with neon, gently heat a point on the tubulation tube near the unit or on the manifold side of the mercury trap if an argon unit. Even a filled tube is under vacuum relative to atmospheric pressure and so easily seals closed once heated to molten. Avoid glass build-up at the seal-off point or the glass may strain, crack then leak. Do this by quickly peeling the unit away once the tubulation tube begins to collapse. Follow the unit with the torch.

    13) Now burn-in the unit. Let it run on a slightly oversized transformer until its color stabilizes and no other problems develop. Some shops burn-in a tube for only fifteen minutes. Others burn-in a unit for eight hours or longer. Longer burn-in times can assure fewer tube troubles after installation.

    14) If the unit is an argon/mercury tube, let the electrodes cool to room temperature then roll the droplet of mercury through the tube covering each electrode. Finally, burn-in again until the tube is bright mercury blue in color.

    Not Finished Yet
    These are the minimum steps used to process a tube. But before the tube goes out the door, there's more work to be done.

    Blockout all appropriate tube lengths including any connection tubes between letters, electrodes and the bends they're connected to, essentially any tube that should not be visibly lit. I've actually seen new neon signs installed with no tubes blocked-out and wondered why anyone paid for the sign; it was barely legible.

    Once properly blocked-out, mount and insulate as needed according to local codes. Yes, neon installation codes sometimes vary from region to region, even city to city. So, before mounting or installing any neon tube, discover and conform to local authority rules that govern your neon sign.

    This article series was offered as one possible course outline for the self-trained neon craftsman. Though there is no substitute for hands-on training under a journeyman tradesman, many wannabes will never get that chance. Even so, realize this: an honest journeyman craftsman will admit that after years of glassblowing there are always new lessons to be learned and at some point even they become self-taught.

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