PRINCIPLES OF FLAMEWORKING TUBING

by Robert A. Mickelsen

Of all of the many lampworkers I have encountered in my nearly 20 years in this business, only a handful have been really good with tubing. The vast majority of artistic lampworkers today are strictly "glass sculptors", who know little or nothing about working with tubing. It is difficult for me to understand this because, in my opinion, flameworking tubing and rod go hand-in-hand. One compliments the other. The very same skills apply to both, albeit with slightly differing purposes. When I was first learning to blow hollow shapes, I discovered that the skills I developed for tubing improved my solid work, and that the skills I already used with the solids, applied to the tubing. Any lampworker who never learns tubing cheats him/herself out of some of the most fun and gratifying work a lampworker can do. So it is my belief that every lampworker should at least know the basics for working with tubing. This article is an attempt to document what I believe those basics skills are.


HAND POSITIONS

Let's start with some basic mechanics. First, hand positions. Not surprisingly, the proper hand position for most tubing work is the same as for most solid rod work: left hand palm-down, right hand palm-up (opposite if you are left-handed). The left hand is the control hand, and the right hand is the guiding hand. In this position, you are best able to control the many variables which will present themselves during any given procedure. You are also able to bring the right point up to your mouth for blowing more easily. (see figure 1)

Although it is not technically incorrect to swap hand positions, I do not advise it unless you are truly ambidextrous. The two hands perform very different functions, and once they are taught, it is as difficult to teach one hand to do the other's task as it is to write with the wrong hand. So, the procedure itself must be adapted to the tasks each hand has learned. If, for instance, you need to close the open end of the point and open the other end, you must also switch ends so that the right hand still holds the open point.

There are a few exceptions to this rule. If the tube or rod you are holding is very large or otherwise awkward, you should hold the piece with both hands palm down. This is because that is the position that your hands are strongest in. An example of this is when you are pulling points. (I will describe that in detail later.) You can also use the two hands down position if you are doing a task which requires very precise control and you do not have the confidence in your right hand with the palm up. An example would be if you are attaching a handle to the exact center of a fairly small piece using a very small seal. The only other reason ever to come out of the left-hand-down-right-hand-up position is in case of fatigue, in which case you should probably take a break anyway.


SPINNING THE TUBE

The second basic skill is spinning. When you work with tubing in a one-directional flame, you can only heat from one side. This means, to heat the tubing all around, you must spin the tubing in the flame. Obviously, since glass absorbs heat like a sponge, the more evenly you spin the glass, the more evenly you apply the heat. The glass is spun by holding the tips of the points in your fingertips and, with a twisting motion, turning the point. Clearly, the twist can only go so far before you have to let go of the point and re- position your fingertips to begin another twist. This creates two problems. First, it defeats the purpose of the spinning because the glass must stop rotating while you re-position your fingers. Second, you have to let go of the glass to do that, but how do you do so without dropping it? Ah... good thing you have two hands, yes?

The problem is solved by alternating the twisting action so that, while the left hand is repositioning the fingers, the right hand picks up the spin, and vice versa. With a little practice, you can learn to coordinate your hands so that you can spin the tube at a very consistent rate. The second problem is solved by a subtle variation in the hand positions. The left hand (palm down) is held so that the thumb and first three fingers do the twisting but the pinky is curled up so that it holds the very tip of the point. So, when the fingers reposition for the next twist, the pinky keeps you from dropping that end. The right hand (palm up) also uses the pinky, but in a slightly different way. The thumb and first three fingers provide the twisting action, but the pinky is held extended, like a strut, and supports the point by balancing it on the tip! (long fingernails can help here.) This is not as precarious as it may sound. If the point falls off the pinky, it will fall no farther than the palm of the hand.

So how fast should you rotate the glass in the flame? It depends on what you are doing. Rotation can vary from very fast (preheating) to very slow (cutting off). It will also vary as the glass gets softer. Obviously, as the glass becomes hotter and softer, you will not be able to spin it as fast as when it was cooler. There is also a tendency for one hand to lag behind the other over a period of time producing a twist in the tube. To avoid this, I usually do not spin just one way. While I am just heating up a piece, I will spin back and forth, six to ten turns each way. As the glass gets hot and softer, I reduce that to three to five turns each way, and then cut down to one to two turns each way as the glass gets really soft. I call this bi-directional spinning. I will spend more time on the subtleties of spinning later.


PULLING A POINT

The first skill you must learn is pulling a point. Before you begin, and as a rule before any procedure, you must clean the glass of any dust or fingerprints. With tubing, this means inside and out. Squirt some glass cleaner into each end of the tube and wad up one or two paper towels and stuff them into one end. Using a wooden dowel like a ramrod (do not use a glass rod!), push the wad through the tube. Then clean the outside of the tube. Now you are ready to begin.

Tubing comes in many sizes and wall thicknesses. I generally prefer to use medium to heavy wall tubing because it hold the heat longer and makes stronger points. 25mm medium wall tubing is a good size to start with.

Begin with your two hands positioned about ten to twelve inches from the ends of the 4' tube (at about 25% and 75% of the length of the tube), both hands palm down. Begin a steady rotation turning the tube so that the top turns toward you. Concentrate on trying to turn the tube at a steady rate, about one full turn every three seconds or so. There may be a tendency to "bounce" the tube up and down until you become adept at this, so try to keep it steady as you turn it. Begin by holding the center of the tube just above the flickering end of the visible flame. This is the "warm-up zone". The temperature is fairly hot, but not so hot as to shock the glass. Unlike solid rod, you should avoid plunging a cold tube directly into a hot flame. Warm it up for ten to fifteen seconds, and then gradually work your way down into the flame reaching the optimum part of the flame within about 10 to 15 seconds after you start (20 to 30 seconds for larger tubing). You should be rotating the tube steadily before, during, and after the heating process as well as throughout the pull. As the glass softens, you will notice a tendency to draw apart the tube. It may be necessary to deliberately push the glass together slightly to avoid this. You will also notice that control becomes much more difficult as the glass softens. You will have to control each half of the tube virtually independently of the other to keep them lined up. (This is why it is so important to place your hands at 25% and 75% when you begin, so each half will be balanced in your hand.) Welcome to the world of tubing!

When the glass is sufficiently soft, and without breaking your rotational rhythm, remove the tubing from the flame and begin slowly drawing the glass apart. Right away you will see if the tube is heated evenly. If it is, it should be relatively easy to keep the drawn portion of the tube on center. If it is not, it will be pulled off to one side. You can sometimes correct this by turning the hotter side down to let gravity pull the drawn glass down closer to center. As you draw the heated tube apart, it is very important to keep your eyes on the control points which are forming where the heated glass meets the full diameter tube. These points get further and further apart as you draw so trying to watch them both eventually gets to be like watching a ping-pong game with your gaze shifting back and forth every second or so. You have to watch these points most carefully just as the glass finishes setting up at the end of the pull. This is because the point is thickest at the control points and therefore takes the longest to cool. (see figure 2) Whatever happens, you only have about seven or eight seconds to complete the pull so you must go ahead even if the point is off center. You can correct errant points later. For your first few dozen points, you should count to yourself to get a feel for the timing: "one- thousand one, one-thousand two,...etc." You should try to achieve a pull of between 15 and eighteen inches within seven to eight seconds. You should reach the maximum pull at the precise moment the glass sets up, but continue to rotate the glass even after the pull is complete. Then, return to the flame and burn the pull in half to separate the two sides and then, and only then, do you stop your rotation.

Your second point is done the same as the first, only you will be holding onto a point with your left hand instead of a tube. If the point is not centered and straight, you must correct that before proceeding. If the point is not salvageable, pull another from the same end. Once you have one good point to pull from, you need to decide how much glass is required for the planned procedure. For now, let's go for 2" of tubing. Begin by heating the "break" where the point meets the full diameter of the tube, but do not heat until it is soft. Just a couple of rotations until there is enough heat in the glass to keep it from shocking. Then, work the flame down the tube slowly until it is 2" from the break. Continue heating at that spot until the glass is soft and pull another point. Set the hot point in the cooling rack and the hot tube down on your "safe" place. Care should be taken not to let the hot end touch anything because the contact could shock the glass enough to cause it to crack. Pick up the second half and repeat the procedure. You should continue until you have pulled the entire tube, alternating tubing halves for each pull. That way, you are less likely to inadvertently grab a hot point. When you are done with each point, set it in your cooling rack making sure that the hot point does not touch any other points or objects that may be standing in the rack.

If this is your first time working with tubing, count on throwing away quite a bit of glass. Your first points are not likely to be useable or salvageable. If you pull a successful point within the first tube you break down, you are well ahead of the game. If you do not, don't get discouraged. You didn't think this would be easy did you? The fundamentals you learn from just pulling points are the same ones you will be using in every tubing procedure you ever learn. Get pulling points right, and the rest will come easy.


BASIC HEATING PRINCIPLES

Now that you have successfully pulled a few points, it is time to learn to blow a bubble. But first I want to discuss a few basic principles about heating. Remember I said that glass absorbs heat like a sponge? When you heat glass in a flame, anyplace that is heated unevenly will effect the final shape no matter what you do to it later. Heat can be thought of as building up in layers, kind of like masonry. Start with a level foundation and your structure will be level. If your foundation is crooked, your structure will also be crooked. In fact, I use a method of preheating I call "foundation heating" that is nothing more than making sure that the first 1000 degrees of temperature is applied as evenly as possible (see figure 3). To do this, I pre-heat my points in the "warm-up zone" for 10 - 15 seconds, and then bring the glass down slowly into the flame. I do this step while spinning the point very fast, probably three or four rotations per second. I heat the glass in this manner just until it begins to glow. At this point, the glass is at about 1200 F and is heated perfectly evenly... a sound foundation. This is the first principle of heating. Every tubing procedure I do is begun this way.

To the casual observer, it appears like I manipulate the glass and control its shape with my hands. However, nothing could be further from the truth. It is the heat and the way I apply it that controls the shape. My hands are just guides and supports and a mechanism for rotation. If I want a perfectly round bubble, I heat the entire point as evenly as possible. If I want a bubble that is broader on one end than the other, I use a gradient of heat to produce that shape. This is the second principle of heating: Gradient heating. The gradient controls the shape. This gradient can be simple or very complex, as simple or complex as the intended shape. It can be accomplished in one step or as a result of a series of steps. There are no manipulative mistakes in lampworking (besides an outright fumble). There are only heating mistakes. If something goes wrong, it is because of incorrect application of the heat.

Flames are endlessly variable. One of the most difficult things for beginners to learn is how to adjust the flame properly each time you light up. To simplify this dilemma, you should think of the flame in terms of its volume. Flames should always be of a volume that is appropriate for the task at hand. When working a large piece of glass, use a high-volume flame. When working a small piece, use a low-volume flame. On the surface, this may seem so obvious as to be silly, but it is easier said than learned. You can always spot an inexperienced lampworker as opposed to an experienced one. The experienced one will constantly be changing his flame, adjusting it every time he changes his procedure. The inexperienced one will struggle through his entire process without ever touching his valves. So, the third principle of heating is volume... the right tool for the job!


KEYS TO CONTROL

So are we ready to blow a bubble? Not yet! We have a few more basic principles to discuss. These have to do with control. There are three keys to control: control points, centering and concentricity, and correct heating. Let's take these one at a time.

A control point is the spot where your handle (or point) meets the object you are working on, whether it is tubing or solid. It is very important that control points be centered to the axis of rotation. If viewed from the end, the control point needs to be in the center of the bull's eye, so to speak. If you find in the course of your procedure that your control point is not centered, stop what you are doing and center it before going any further. This is especially true for tubing. The slightest wobble caused by off-center control points will result in uneven bubbles and will be magnified tenfold through the remainder of your procedure.

A similar and often related factor is concentricity. When working tubing, the axis of rotation should always be perfectly straight. If it is not, or if it gets off a little bit during the procedure, you should take a moment to straighten it before continuing. Again, small variations in the axis of rotation translate into large errors by the end of a procedure. Control points and concentricity may seem very much alike, and they are related to each other, but they are not the same! In order if priority, first, center the control points, then re-align the axis of rotation (see figure 4).

Finally, it is vital to use the correct heating for the job. Beginner lampworkers almost always overheat the glass and then wonder why they lose control. I cannot emphasize this enough: Heat the glass just enough to accomplish the task at hand AND NO MORE! There are a great many tasks that require just warming up the glass to move a little, no more. This is an area that takes practice to develop a feel for. One way to tell is to constantly be moving the glass a little to see how it reacts. These movements consist of little tugs and pulls that will give you an indication of how things are going without distorting the shape of the piece too drastically. Another way is to take the cautious approach of doing every task in little steps instead of all at once. This method takes more time, but vastly reduces mistakes, which, more often than not, more than makes up for the additional time taken to do it in steps. I am a 20-year lampworker and I still do a great many things in steps, just to eliminate errors.


BLOWING A BUBBLE

OK, OK! So let's quit yapping and melt some glass already! Let's see if we can apply the basic principles and keys to control we have discussed and blow a bubble. Take one of those 2" points you pulled (try to pick one with salvageable points) and open one end with your glass knife. Spin the point in the warm-up zone and watch the control points to see if they need to be centered. If they do, once the point is warmed up, bring it down into the flame slowly. With your right hand, reduce the volume of your flame by turning down the gas until the flame is very sharp and hot. Aim the flame directly onto the "break", which is just above the control point, and heat it until it begins to soften. Then, using gravity to draw it down and a slight pull to straighten it out, center the point as needed. Then repeat for the other side.

Now, increase your flame volume back to where it was by turning up the gas and add a little oxygen to make the flame hotter. Begin heating the entire tube as evenly as possible by spinning and moving the tubing slowly laterally back and forth. You should be alternating the direction of your spin about every ten turns or so. Try to keep everything very deliberate and rhythmic. Move laterally as necessary to heat the entire tube, but move at a perfectly even rate, slow and steady. Watch for the color to come into the glass as it heats up. As the tube starts to take on a pinkish-orange glow, you will notice that it also is becoming softer. You will have to reduce the number of rotations in each direction to four or five, and then two or three, and then finally just one or two. You want the glass to be soft enough to be able to easiy change its shape by blowing, but not so soft that you no longer are able to control the bubble. This is the "working temperature". It is at this temperature that you will be doing all the shaping and decoration necessary to transform the tube into a work of art.

If there are any unevenly heated areas on the tube, they will "flash" at you as you spin the tube around because the hot spots will have a brighter glow to them. If you have heated the tube properly, it will have a lovely pink-orange glow that is perfectly even all around, and the walls of the tube will begin to collapse. Quickly swing the point 90 degrees so that the right (open) end is in your mouth and the left (closed) end is directly away from you. For now, hold the point as level as possible. While continuing to rotate, blow gently into the tube to expand the walls. You must judge how hard to blow by how easily the walls expand. Just like in point pulling, the blow should be completed at the precise moment the glass sets up, usually about seven or eight seconds. You will find that you can effect the shape of the bubble as you blow it by bending the axis of rotation in the direction you want to bubble to blow out. In this manner, and by finishing the blow with pulling pressure directly along the axis of rotation, you can blow a perfectly round bubble (see figure 5). Is yours round? Probably not. Don't worry, it will be awhile before you can consistently blow round bubbles. Blow a hundred and check back with me.


FLARING

Besides blowing a bubble, the second most commonly used tubing technique is that of opening and flaring ends. Tops of vessels, the feet of goblets, and even as a decorative technique in some complex sculptures, there is no end to the possible uses of a neatly flared end. There are a couple of principle concepts that govern how flaring works that you need to understand before we try one.

The first is the concept of wall thickness. It is one thing to blow a round bubble, but if the wall thickness is not consistent all the way around the bubble, the roundness is an illusion. When you go to open and flare a bubble with uneven wall thickness, the illusion is revealed and then magnified as the flare progresses. This is the most difficult part of flaring to master, and becomes much more difficult as you introduce overlaid colored glass decorations into the bubble. The key is to control wall thickness. Concentrate on keeping it as even as possible, even if it means that your bubble is not as symmetrical as it might have been otherwise.

The second concept is our old friend heat gradient, only with flares it is a critical factor. Since the lip of the flare must stretch the most, it must recieve the most heat. The heat must then be gradually tapered toward the center of the flare to produce the desired conical or disk-like shape. The shape is controlled by a combination of heat gradient and the angle that the bubble is held while flaring. Hold it horizontally and the lip will kick out almost perpendicular to the axis of rotation. Hold it at about a 45 degree angle and the flare will be more conical.

The third concept is timing. You cannot rush a flare. The timing is determined by the heat gradient and flame temperature and, of course, by the efficiency of the lampworker. The glass should never be pushed into position if you can help it. It should just move into the desired shape because you heated it to do that. Of course, very few of us will be able to do that successfully every time which means, when you aren't successful you have to...

...Adjust! Since flaring is so difficult, we must consider adjusting for error as the fourth basic concept. The most common adjustment I make is to attach a finger holder to the flared end and re-center the control point, which has moved out of center for whatever reason. This simple adjustment saves countless flares from the trash can every year for me. It is only one of dozens of little tricks I have learned and I actually could write an entire paper on them alone, but for the scope of this article, I will just discuss re-centering and leave the reader to explore the rest on his own.


FLARING A BUBBLE

As our example, we will make a small derby-shaped flare similar to what I would use as a goblet foot. This flare ends up with a slightly domed center and a flattened rim that sets at nearly 90 degrees to the axis of rotation. The graceful venetian shape that results is both beautiful and functional.

Begin by pulling a three-inch point from 25mm tubing. Blow this point into a small bubble, but do not stretch it to make it round. Instead, while you are blowing the bubble, push the points together slightly to produce a slightly flattened bubble, more oblong than round. Ideally, you want a bubble that is around 2 inches in diameter and about one and a half inches in length. After the bubble is blown, examine it carefully. Check the bubble for centered control points and, more importantly, consistent wall thickness at the control point. You can see the wall thickness through the edges of the bubble. Rotate the bubble slowly and watch the wall thickness. If it is uneven, you will be able to see it as you rotate. If it is even, you will be able to see that too. Select the end that is most even and burn off the point at the other end. Be sure to leave the remaining point open. Heat the nub where the point was attached and marver that end into a smooth conic shape using your graphite paddle. You want the cone to be flat enough to be a continuation of the oblong shape of the bubble. Then, using an 8mm rod, attach a small blob of solid glass to the tip of the cone. Make sure this is a good, hot seal. You may have to blow into the other point to prevent the bubble from collapsing. Draw the rod slightly to center it and burn it off, leaving about a half inch of 8mm rod still attached. Melt the end of this blob into a ball and flatten the end slightly. This is called an "avolio", and will be the attachment piece when the flared base is added to the completed vessel. Now, attach a fifteen inch piece of 6mm rod to the avolio, being careful to keep it perfectly concentric.

Swap hands so that the open point is in your right hand and begin heating a narrow band of glass right below the control point. Use the edges of your flame so as to heat as narrow a band of glass as possible. When the glass is sufficiently softened, quickly swing the open point up to your mouth and blow, while at the same time drawing the point apart. You will have to be fairly quick about this, but do not blow too hard or you will burst the bubble. This is not dangerous, but it can be loud and startling! This should result in a long tissue-thin bubble that you can then break away with a file. Gently clean up the edges of the blown-out tube. Finally, use a shears to trim away the remaining jagged or uneven glass. You are ready to begin flaring. (see figure 6)

You start your heat at the lip, melting it until it is smooth. Gradually move the flame around the side of the bubble so that the lip and first half-inch or so of the tube is being heated. Insert your graphite flaring tool into the opening and allow the inside edge of the tube to rest its weight upon it while you rotate. Immediately you will see the opening get a little wider. Continue to heat from the lip back up the bubble a little further, increasing the amount of glass that is softened as the flare gets wider. Try to avoid deliberately pressing the tube against the flaring tool. The weight of the tube should be sufficient to cause the tube to move if it is heated properly. When the opening is approximately half of the diameter of the bubble, you should remove the graphite tool and continue to heat the lip until the flare begins to widen on its own. If you have kept the bubble's wall thickness even and the opening centered, the flare should be very easy to control. You will find that increasing the speed of rotation will kick the lip out more and decreasing the speed will allow more of the bubble to get involved in the flare. Changing your angle from horizontal to more tilted will cause the flare to droop and will result in more of a hyperbolic shape. There is much debate about the esthetics of a good flare, but only you can decide for your work what is best. The flare will continue to open with more spinning until you have what you want. The procedure is the same for bowl-shaped flares as it is for perfectly flat goblet feet. For this exercise, we want a flare with a slightly domed center tapering out to a fairly flat lip. To get the lip as flat as possible, the final spinning should be as rapid as you can make it without dropping the glass. I have seen some lampworkers place the handle between their hands and spin it by rubbing their hands together furiously! Then, quickly bring the flare down to your marver board and apply slight pressure to insure that the flare will have a perfectly level lip. Set the flare down on your marver board and check to see that it sits securely without rocking. If all goes properly, you should find yourself with a nice flared goblet foot in just a few minutes. (see figure 6)


COLORED DECORATIONS ON TUBING

Decorating clear tubing with colored glass is as old as flameworking itself. Every type of direct decorating involves applying colored glass to the surface of the tubing and then melting it in. There are a bazillion different kinds of decorating techniques, but they all share one common truth: to varying degrees, they all mess up the consistent wall thickness of manufactured tubing. So, the primary task of decorating is, once the decoration has been applied, to restore the consistency of the wall thickness to the point where bubbles and flares can be controlled.

This is accomplished by a method called 'shrinking' the glass. The idea is that if the tube is shrunk down to half its original diameter (and so twice the original thickness), when it is blown out again, the wall thickness will be consistent. This is nice in theory, but difficult in practice. But it is the only solution to the problem, so we are stuck with it. So, rather than try to describe the many different methods of decoration (which are for the most part very simple and easy to learn), we will instead discuss this process of melting in the decoration, shrinking the tubing, and blowing it out again, and the various problems you might encounter.

With borosilicate glass, one of the most difficult things to master is the control of a piece of glass with widely varying viscosities as you often have with decorated tubing. Clear glass is relatively soft and pliable when hot. Many colors, on the other hand, are stiff and viscous at the same temperature. Clearly, this is going to lead to problems in trying to control blown shapes. There isn't much that can be done about the varying viscosity, but you can take it into account when you apply the decoration. It makes sense that if the decoration is all piled up in one spot, there is no way to ever achieve any kind of symmetry in the final blown shape. Therefore, you should make every effort to distribute the color decoration in as even a manner as is possible, or to select decorative methods that do so. Such methods as the application of frit and spin-trailing are good examples of this. Another is striping, provided that the stripes are evenly distributed. Even a technique such as shard application, which is by nature much more random, can be done carefully so as to provide as even a distribution of color as possible. (see figure 7)


DECORATING A CLEAR TUBE

As our exercise, we will do a layered decoration that we will blow into a flared bubble such as might be use for a goblet top. Begin with a 3" point of 35mm heavy wall tubing. Heat it up, being sure to lay down a good foundation of heat. When it is up to temperature, sprinkle some colored frit, multi-green for instance, onto your marver board. Shake the board to spread out the frit in a nice even manner. Heat your point until it glows but not so hot that it starts to become misshapen. Then, move quickly from the flame to the marver board and roll the tube over the frit. Watch to see that the frit is applied as evenly as possible. Repeat if necessary. Then, using a medium oxidizing flame and starting at one end moving slowly toward the other, melt in the frit until the surface is again smooth. The walls will want to collapse so you will have to be careful to keep the point on center. Blow into the tube enough to keep it round, but not enough to expand it. At the end of the procedure, you should have a fairly consistent oval shape with concentric points and centered control points. If you don't, take time now to fix them.

Next, let's apply some spin trailing. Pick another color, ruby red for instance, and select a rod with a nice clean end. Set it where it is handy. Place a 'yoke' (a device used for spinning points with one hand) in front of your torch where the point can rest in it with the tube in a convenient location for applying the trailing. Heat the tube until it is glowing, but not so much that it is soft. At the same time, heat the end of the ruby rod you selected until is very hot and molten. When the two components are properly heated, quickly set the point in the notch and stick the molten tip of the rod directly on the control point of the handle you are holding. Draw the glass out into a thin strand and begin spinning the tube away from you as fast as you can make it spin. Guide the strand up the tube so that the trailing covers the entire tube. You have only about four of five seconds to complete the trailing so you must move quickly. Then, immediately return the tube to the flame and melt in the trailing. If you hesitate, the strands will cool down and pop off the tube before you can melt them in. Repeat the process if you want more trailing.

Finally, let's apply some drawn patterns. Let's use cobalt blue glass because it is a very viscous glass. Heat up about an inch of cobalt blue and, using a tweezers, draw out the end into a thin (about 1/32") strand. Heat your tube until it glows and then, using a small, tight, oxidizing flame, melt the strand onto the tube. You can "draw" with this method anything you want from random squiggles to recognizable shapes. Just remember that anywhere you concentrate the cobalt will result in difficulties controlling the shape of the bubble. Repeat if you want more drawn decorations.

Increase the volume of your flame and melt the decorations in as you did after the frit and trailing, but this time, continue heating after the decorations are melted in. You want to shrink the tube down to about half its original size. You may have to stop repeatedly to regain control since the glass will be very hot and soft. Blow into it to keep it round but not to expand it. You will notice that the glass will begin to behave as one piece of glass instead of many. When, during your attempts to keep the glass round and on center, you notice that the glass is moving uniformly, it is time to blow the bubble. Blow it out slowly just like you did the clear bubble, making adjustments as you blow to keep the bubble centered and symmetrical. Keep blowing until you have a fairly large bubble, maybe four inches in diameter. Seal one end and add an avolio as you did with he previous flare. Open and flare the bubble until you have the shape you desire, in this case, a goblet bowl. (see figure 8)


POTENTIAL PROBLEMS

Not surprisingly, there are a great many things that can go wrong with this process. The most common is lack of symmetry due to the colored decoration not being melted in enough or applied in an uneven manner. Another is an uneven lip for the same reason. Not much can be done about either of these once the bubble is blown and the lip flared. The solution is to avoid these problems by distributing the color evenly and by melting in the decorations thoroughly before blowing. Another very serious problem that I have encountered is devitrification caused by overworking the glass. Once devitrification has occurred, it can be very difficult to get rid of. It is very unsightly and even a little can ruin a piece. Devitrification looks like fog on the surface of the glass. If you try to heat it, sometimes it will disappear only to reappear as the glass cools and sometimes it will just boil violently. There are a couple of things you can do to avoid devitrification. One is to keep your oxygen line pressure below 25 lbs. Devitrification is a much more prevalent problem with surface-mix burners than with pre-mix burners, so if you are experiencing this problem, try switching to a pre-mix torch. Finally, try to avoid over- working the glass. Don't heat it any more than is necessary to accomplish the immediate task.


SUMMARY

I have been a full-time lampworker for over 20 years. I have probably spent around half of that time working tubing. If I were to estimate hours, I would have to guess at somewhere between 15000 and 20000 hours spent lampworking tubing. There are still a great many things I need to practice, to learn to do them better. Clearly, lampworking tubing is not something that can be mastered in a short time. However, a competent lampworker can learn to blow quality tubing with reasonable consistency in a fairly short time, provided he starts with the basic principles described in this article. Foundation heating, control points, bi-directional spinning, and proper heat gradients, are all things that I learned the hard way, from failure after bitter failure. Hopefully, giving you this information up front will save you some of that frustration.


Robert A. Mickelsen