BOMBARDING TOOLS

IN MY MANY YEARS of glassblowing I have seen and heard of a whole variety of different tools and bombarding procedures, which are all trying to achieve the same end results, the best possible neon. I won't be going into the bombarding procedures here, but I will try and cover many useful tools that I have found to be very helpful.

In the May 1987 issue of SIGNS OF THE TIMES, I wrote an article,
NEW AGE PUMPING SYSTEM, describing how to design and build your own manifold system using greaseless, O-ring type stopcocks.(PHOTO)  I had used them for several years prior to the article, and I am happy to say that they still, in my opinion, are the only type that neon manufacturer's should be using. These stopcocks have probably been the single most important advancement for neon bombarding in the last decade. They are virtually leak free, and the room temperature has little or no effect on their operation. With periodic cleaning, and replacement of the o-rings themselves, you should have years and years of faithful service.

When the o-rings are replaced and for first time use, I have found that placing a small film of stopcock grease specially designed for these type o-rings helps them to slide easier in the glass housing. Use as little as possible to keep the stopcock clean.

In the event you should get some butylpthalate on the fill gauge (PHOTO)  stopcock rings, they should be cleaned immediately because some of them will have a chemical reaction and deteriorate.(UPDATE)

The one drawback to the average glassblower who uses these stopcocks is the fact that they are made out of Pyrex(r) glass and require expensive graded seals to attach to lead glass. But fortunately, there is now such a variety of compression fittings available on the market that this creates no problem for hooking up to the lead glass that neon glassblower's are accustomed to working with. The neon glassblower is able to make simple bends and welds with Pyrex(r) tubing by turning their fires extremely high, but any detailed work should be left to the glassblowers with the proper flames and equipment.

 (PHOTO OF FOLLOWING ITEMS)
(DRAWING POINTING TO DESCRIBED ITEMS)

 For storing and injecting mercury into tubulation glass, there is a variety of hard glass bottles with ground seals and glass stoppers to help keep the mercury as contamination free as possible. For cleaning up mercury spills, there are many different product and mercury cleanup kits available for taking care of this problem.

As far as the mercury traps used on the manifold itself, the one I prefer to use is the raised arm, dead end type . They're easily made, so you can discard them when they become contaminated. To make one, it's handy to have the single tip hand torch I mentioned in part II,GLASSBLOWING FIRES.

First pick the desired size tubing and make a 90ø bend. Then seal off the tube approximately 1-2" from the bend and slightly blow it out to keep the glass the same thickness. Use the single tip hand torch to blow a hole slightly larger, or smaller depending on which works best for you, than the diameter of the tubing on the other side of the 90ø approximately 1-2" from the bend on the opposite side of the drop off, and then weld on another piece of tubing to this hole.

Now make a 90ø bend as close to the "T" section as possible toward the drop off, and then make a drop heat to bring the two tubes into alignment with each other. The only task left is to draw the front of the trap down to tubulation size and attach a piece of glass. Then you're finished.(UPDATE)

I have experienced some pretty severe cracks and other related problems during bombarding, and this type of trap has performed very well as far as keeping the mercury out of the main branch of the manifold.

Unfortunately, mercury does sometimes get into the main branch of the manifold, and for this problem I use a mercury vacuum cleaner. You can easily make one with a small clear jar with a vacuum tight lid, some blow hose tubing, and tubulation glass.

Start by drilling 2 holes the diameter of the tubulation glass in the lid. Insert two pieces of glass tubing approx. 2" long centered in the holes and silicone securely in place to make an air tight fit.

The lengths of the blow hose will vary according to the length you will be from your vacuum source and where you want to clean up. By snaking the blow hose through the branch of the manifold, you are able to vacuum up a lot of the debris and mercury quickly without having to disassemble the manifold. When you get to the point where you're going to vacuum, you may need to seal the blow hose inlet with your fingers or something else to create a vacuum seal.

When the main branch of the manifold becomes quite dirty, reagent grade acetone will adequately clean it so you can delay making a new one. Don't use the hardware store variety; pure lab quality acetone will leave little or no residue.

When bombarding neon tubes, one of the worst problems that arises is when the high voltage electricity arcs through places where two sections of the glass are very close to each other. This can usually be prevented with mica, but I have seen the electricity arc through or around mica. Therefore I recommend using the thickest possible mica and as large of a piece as possible.

An additional measure that can be taken to avoid this problem is the use of a JACOB'S LADDER. This is done by having two exposed wires in close proximity to each other somewhere in the high voltage line before the tube being bombed. I have seen them installed between the two post's of the transformer, or if an overhead line is used, between these two lines. The wire that is used should be of a large diameter because when the electricity arcs across at this point, there is considerable heat generated.

As the pressure builds up in the tube, the electricity looks for the shortest route to complete the circuit, therefore you have the possibility for arc through. With the use of a jacob's ladder, usually the current will arc across at this point, (PHOTO) instead of at the tube. The two wires should be approximately 3/8" apart, depending on your particular bombing setup By experimenting with the gap between the two wires, you should be able to find a position where the tubes will light up at the desired pressure, and the jacob's ladder will arc across before the tube will. This creates a hot electrical flash between the two wires, and is very dangerous, so be careful of the location you place the jacob's ladder. Be sure that you or any other person in the vicinity can not come into contact with the wires at any time. One other helpful aspect of this procedure, is that it also keeps the transformer from arcing across inside and burning out the transformer.

When arc through does happen in a neon tube, I have found that the majority of the time you can save the unit by using the single tip hand torch and some tubulation glass drawn down to a small point, similar to a pencil. Spread apart the tube to allow easy access to the holes, and by slowly heating the area around the hole and then gently sticking the point of the tubulation glass into it and pulling off as small an amount of glass as possible to fill the hole. Then continuing to heat it until the glass has fully sealed the hole. It doesn't work all the time, but with a little practice, this procedure can save a lot of time. (UPDATE)

The spark coil is a very useful tool to have around. It is designed for finding leaks in tubes and giving a rough estimate of how good of a vacuum you are getting. I like to have a small mirror around to place under the tube that I am looking for a leak in, to find those leaks on the bottom and back side of tubes. It also is very useful for finding studs in walls, by sparking to the metal screws or nails.

There are times when a spark coil is unable to find a hole in a unit or the manifold, so there is another procedure that I use in this situation. To do this, I weld together two 12mm electrodes, one tubulated, with the mica removed and approximately 1/2" space between the two ceramic collars. Then the electrodes are bombarded carefully. By attaching this unit to the manifold and using as small a transformer as possible connected between the two leads, under a vacuum this will cause a glow between the two electrodes when there is a small leak, or an insufficient vacuum. The color seen depends on the amount of vacuum being pulled. It usually is a dull purple. By putting a small amount of acetone in a plastic bottle with a very small tip (like those used with methaline-chloride for melting plastic) and squirting a small amount over each suspected area, one at a time, and then examining the color between the two electrodes you may find the leak. The color will change to a whitish blue when the acetone vapors are pulled into the system. If you have an electronic high vacuum gauge, you will see a dramatic rise in the pressure when the acetone enters the system, caused by the vaporizing of the acetone, and therefore the double electrode system just mentioned isn't actually necessary.

All electrode manufacturer's have a recommended procedure for bombarding there electrodes, and it is very important to be able to monitor the vacuum, electrical current and temperature during this process.

 (PHOTO OF SEVERAL DIFFERENT GAUGES)

There has been a steady rise in the number of shops that now have electronic vacuum gauges. These are a must for noting any small changes in the vacuum systems efficiency, very small leaks in tubes, and knowing when a tube has achieved it's maximum vacuum. The only drawback to these types of gauges is that over a period of time, they can become contaminated from the mercury and various other items found in the system. Therefore, I recommend that you purchase a filtering/ground coupling that is installed between the gauge tube and the vacuum system.

To check the accuracy of the fill gauge, there is a simple test that can be performed. To do this you need a 1/2" X 1" piece of paper, masking tape, 1/2 lb. of mercury, and a stick of tubulation glass.

Take the piece of paper and place a very thin line 5mm from the top and label it 0. Then descending downward from this line, draw lines at 5,10,15, and 20mm. Place a small piece of masking tape on the top and bottom of the paper with the sticky side towards the numbers.

Bend the tubulation glass so that it will hook up to the manifold and drop down to the floor in an easily accessible area. You will need at least 35" of room vertically from the floor to the first bend. Have the tubulation glass come directly over the edge of the table and down the side so that it can be secured to the table with masking tape. Place the bottle of mercury on the floor and cut the tubulation so that it is 1/8" from the bottom of the bottle.

Place the tubulation glass into the bottle of mercury and hook it up to the manifold. Secure the tubulation to the table. Now you need to gently open the vacuum stopcock and slowly pull the mercury up the tubulation glass. Be sure that there are no air bubbles in the mercury and that there is plenty of mercury in the bottle to keep from sucking all the mercury into the manifold. If you need to start over for any reason, close the vacuum stopcock and slowly allow air into the manifold to let the mercury gently return to the bottle. Continue this process until the stopcock is fully open and let the system evacuate for several minutes.

Secure the piece of paper to the tubulation glass with the 0 mark exactly at the top of the mercury and close off the vacuum stopcock and your fill gauge stopcock, unless you are using a electronic fill gauge. Now as gently and slowly as possible allow air into the system while someone else watches the mercury. Have them stop you when the mercury is exactly at the 5mm line and then check this with your fill gauge. If there is a discrepancy, place a mark on the fill gauge at this point. Continue this procedure at the 10,15, and 20mm lines. It is very important that the mercury be stopped exactly at the lines to insure accurate readings.

After you have completed this process, slowly allow atmospheric pressure into the system to let the mercury return to the bottle. Use these new marks to recalibrate the manometer or fill gauge. I recommend that this is done more often with electronic fill gauges because they have a tendency to become contaminated causing inaccurate readings.

One electronic device that is very important to have to monitor the voltage passing through a unit during bombarding, is the milliamp meter. The range of the scale should be from 0 to 1 amp, usually with 25 milliamp increments. When installing the gauge, take into consideration that the high voltage will be passing through it, and therefore should not be touched while in operation and is best placed in a remote location where it can easily be seen, but out of reach. Follow the installation instructions carefully to insure proper performance of the gauge.

There are many ways to determine the temperature of the tubes being bombed, from old newspapers to infra-red electronic gauges. The wall temperature that is needed to achieve the best bombing results is in the range of 200-225 C (390-440F).

The simplest way, and least expensive, is the time tested browning of newspaper. At around 170C (340F) the newspaper will brown and start to smoke. When the temperature reaches 220C (425F) the paper will blacken. This is a very crude way of telling the temperature but it has worked satisfactory for glassblowers for generations.

I have seen an older glassblower who had a small device that would sit on the glass while it was being bombarded and it was composed of a spring that would expand as the glass was heated, and on the end of the spring there was a scale with a needle that would point to the various degree markings. There was also an advertisement here. It was probably given away as a promotional item and I couldn't attest to the accuracy, but it was such a simple device it would be nice to see them return to the market.

A more accurate method to determine the temperature is with the use of a special temperature liquid or crayon that melts or changes color at a predetermined temperature. These are accurate to within +-1% and should last for many years. A special note; they should NOT be applied to a unit while the high voltage is running through it. They come in a wide variety of temperatures, so I would pick one in the upper range that you are trying to reach.

There are many different ways of hooking a unit up to the manifold system. Probably the best way is to weld the tubulation directly to the manifold to insure there are no leaks or chance of contamination, but this is a time consuming process and there are several other ways that will save time and if used correctly, will achieve satisfactory results.

With the increased use of the O-ring style stopcocks and there dependability, there now is a compression fitting on the market that utilizes these o-rings for hooking two pieces of 5mm tubing together. They are very handy and only need to be finger tight to seal the two tubes together. They also allow a small amount of flexibility in the hook up, so that any slight movement of the unit won't break the seal.

In the article on BENDING TOOLS, I mentioned the use of some small heavy walled, high vacuum tubing for swivel hook up to different size glass tubing. This tubing also works very well for hooking units up to the manifold.

One of the distinct advantages of using this tubing is that it allows a lot of flexibility to the unit being bombarded. If you are processing a lot of small units, you can use only one mercury trap over and over again. To do this, you need a 4"-6" and a 1/2" piece of the tubing and a mercury bubble. Cut the tubulation glass approximately 1/4" from the bubble and attach the 1/2" section of tubing to this side. Attach the other section of tubing to the manifold and the other side of the mercury trap. By using one of the plastic bottles that I mentioned earlier for methaline-chloride to inject mercury into the bubble, you can use the same bubble many times.

After the unit is gassed, you can take the unit and by lifting it up and rolling it sideways, the mercury can be entered into the unit without unhooking the unit from the manifold. Then you can tip off the tubulated electrode at the unit, and save one step.

Now for the next unit, all you have to do is remove the glass left from the tubulated electrode, inject some more mercury, hook up the unit and you are ready to go. You should periodically replace the rubber tubing and mercury bubble to help eliminate any possibility of contamination.

One last tool that I would like to mention took a long time to find. There is nothing worse than doing a beautiful work of neon art and then finding out that the label of the glass was in a place where it could be seen. I tried many different things, but until recently all these efforts were futile. Then one day I took a unit to a scientific glassblower and we tried some hydrofluoric acid on a cotton swab, (WARNING: this is some really nasty stuff, so be sure to follow all necessary safety procedures) and by gently rubbing the swab across the label, low and behold, my prayers were answered.

(I have not gone into vacuum pumps here, you may read about them in "TOOLS OF THE TRADE II")

Hopefully I have been able to bring some tools of the trade forward here that you were unaware of that will help you in your quest to make better neon. You may find that by altering some of these tools for your own needs, that other useful tools will probably emerge and I would greatly appreciate your sharing them with me via , and especially any tools that I have not mentioned. You never know; there may be a "TOOLS OF THE TRADE II" in the future.