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The objective of this course is to acquaint the student with basic glassblowing hand operations and techniques. Each class period will begin with a brief demonstration of the particular glass seal to be accomplished, followed by “hands-on” practice of each seal by the student. Successful completion of the course will enable most students to accomplish routine glassblowing tasks encountered in the lab. It will also give you a solid background for preparing sketches and plans that are submitted to the Glass Shop for construction.
The following items will be discussed before we begin the glassblowing lessons:
Safety in the Glass Lab
Most of the safety procedures we will follow are similar to those of any chemistry lab. We will be working around open flames, hot glassware, and sharp edges on the glassware.
The following is a list of important rules for the glass lab:
- Safety glasses are required at all times. ∗ Each student will be provided with a pair of Didymium glassblowing glasses. These glasses filter the bright sodium glare produced when the glass is heated. ∗ Welder’s goggles are required when working quartz or Vycor glass. These goggles filter harmful ultraviolet light produced as the quartz is heated.
- Heat only clean, solvent free glassware. ∗ Never heat glass with volatile or toxic materials inside. If you must heat glassware under these conditions, do so in a hood with a safety shield. Also, attach a trapped blow hose to the glass so that you do not inhale vapors from inside the apparatus. ∗ After rinsing glassware with solvents, air dry the apparatus to make certain that no solvent remains. (Explosion could result.) ∗ Metal vapors must never be present in glass to be heated. The most common metal encountered in glassware is mercury. Remove all traces of mercury before heating and blowing on this glassware. ∗ Silicone stopcock grease is another source of contamination in heated glassware. A fine white powder (silica) is produced when heated to high temperatures. This silica will fire into the glass and, in turn, weaken it.
- Protective clothing ∗ Sandals are not recommended footwear. ∗ Long hair should be tied back when working around open flames. ∗ Avoid wearing synthetic clothing that will burn and melt when exposed to flames or hot glass. ∗ Roll up long sleeves so they won’t catch on fire.
∗ Heat insulated gloves are available to handle hot glassware.
- First Aid ∗ IMMEDIATELY tell instructor you are injured. ∗ For minor cuts, Band-Aids will be available. ∗ Severe cuts may require treatment at the Student Health Center. ∗ For burns, immediate immersion in ice water is the best treatment for minor burns to the hands. An ice bath will be available during all class periods.
- Know location of each of the following: ∗ Fire blanket ∗ Fire extinguisher ∗ Fire alarm ∗ Safety shower ∗ Eye wash
- General safety rules: ∗ Never hand the instructor a piece of hot glassware. ∗ No eating or drinking in the glass lab. ∗ Use common sense. ∗ Report all accidents to the instructor immediately.
Equipment
This section describes the tools and burners that we will be using during the class. Each student will be issued the following equipment:
- Bench mounted torch
- File or glass knife
- Flat graphite
- Graphite rod
- Tweezers
- Corrugated cardboard
- Cork stopper assortment
- Cork stopper with tube assortment
- Ruler
- Blow hose
- Didymium glassblowing glasses
Glassblowing Torch
The torch we will use is a National hand torch which operates with a fuel gas (natural gas, propane, or hydrogen) and compressed air or oxygen. To properly heat the Pyrex^ glass used
Hand Tools
The tools used for forming the glass are made of graphite. The hot glass will stick to almost any other material. Each work area will have graphite rods and flat plates to be used for flaring and flattening the heated glass. These procedures will be demonstrated at the beginning of each class period.
Properties of Common Glasses
There are thousands of different glass types available on the market today. The most common glasses found in the laboratory are, borosilicates (trade names, Pyrex^ and Kimble KG33), soft glass (trade names: Exax, Kimax, Corex, etc.) and Quartz. Before 1920, the most common laboratory glass available was soft glass (commonly called soda glass, or soda lime glass). The following are the chemical and physical properties of the types of glasses.
Soda Glass
Chemical Properties of Soda Glass: Soda Glass: Silica Alumina Calcium oxide Magnesium oxide Sodium oxide Potassium oxide Boric oxide Sulfur trioxide
Typical Composition (%):
Physical Properties of Soda Glass:
Linear Strain Annealing Softening Expansion Point Point Point Coefficient (°C) (°C) (°C) (X 10-7^ )
92 475 510 696
Volumetric ware, television picture tubes, neon signs, household glassware and window glasses continue to be made from soda glass.
Pyrex
Soft glass played an important role in early chemical development, but because it lacks good chemical and thermal shock resistance, other glasses were developed. In the 1920’s a chemical and shock resistant glass was developed by Corning Glass Works called Pyrex. This glass has made many additional chemical applications possible in today’s laboratory.
Chemical Properties of Pyrex :
Pyrex: Silica Alumina Calcium oxide Sodium oxide Potassium oxide Boric oxide
Typical Composition (%):
Physical Properties of Pyrex :
Linear Strain Annealing Softening Expansion Point Point Point Coefficient (°C) (°C) (°C) (X 10-7^ )
32 510 553 819
Pyrex^ has many advantages over soft glass. With a much lower coefficient of expansion, it can be constructed with a much greater wall thickness, and consequently greater mechanical strength, without affecting the thermal shock resistance. Pyrex^ has a greater resistance to chemical attack, is harder and more resistant to surface abrasion, and complex glassware is fabricated and repaired much easier than with soft glasses.
Quartz
Chemical Properties of Quartz:
Quartz: Silica Misc.
Typical Composition (%):
Identifying Unknown Glasses
Several methods will be discussed to identify an unknown type of glass. This will be helpful when trying to repair an existing apparatus of which the composition is unknown.
Glass Fiber Test
Take a sampling of the glass to be tested and form it into a 3-4mm rod. Take a known type of glass and do the same to it. Seal the two rods together and draw into a 12” fiber keeping tension on the fiber as it cools. Burn the fiber through in the flame 3/4 of the way up the fiber. If the fiber curves, the glasses are not similar. A straight fiber means similar glasses.
Physical Test
Glasses may be identified by visual observations of the glass. The following are char- acteristics of each glass:
SOFT GLASS -
- When looking at the end of the tube, you will see a yellow/green color.
- When heated, glass will give a strong sodium glare.
- Fire polishes very rapidly when heated in a neutral flame.
- Without preheating, the glass may crack easily when heated quickly.
- The surface finish is smooth and free of bubbles and imperfections.
PYREX^ -
- When looking at the end of the tube, you will see a green color.
- When heated, glass will give a strong sodium glare.
- When fire polished, it takes a moderate time to flow.
- The surface finish is smooth and free of bubbles and imperfections.
QUARTZ & VYCOR –
- When looking at the end of the tube, a white to light blue color will be seen.
- When heated, no sodium glare will be present.
- When heated, a bright white light will be given off.
- The surface finish may be rough or show tool marks. Vycor may look cloudy and have a rough texture.
- Used or heated quartz may have sublimed silica (a white powder deposit) on part of the tubing.
Annealing Glassware
The annealing of glass seals is important if durable equipment is desired. Internal thermal stress is introduced when the glass is heated above the strain point. (The strain point of Pyrex^ is 510°C). Annealing is the process of heating the glassware to a temperature just below the softening point and then allowing it to cool slowly. This process may be accomplished by heating the glass in electric ovens or with annealing flames.
Locating Thermal Stress with Polarized Light
The presence of residual thermal strain in glass cannot be detected with the unaided eye. By viewing the glassware through a polarized light source, the strain can be easily located. It is known that light transmitted by strain free glass obeys the laws of refraction; and that a ray of light transmitted by strained glass is split into two rays. These rays follow slightly different paths through the glass, they’re planes are polarized and their vibrations are at right angles to one another. If a beam of polarized light is passed through a piece of glassware, and the emergent light is viewed through the analyzer; the regions of glass that are strained will show a brighter light intensity. Areas of bright narrow light bands will cause cracking, and should be reannealed.
Figure 2
Oven Annealing
A large or complicated piece of apparatus may be assumed to be strained after it is blown. Each piece of glassware produced should be oven annealed to insure that it will not crack when it cools. The glass is annealed in a thermostatically controlled electric oven. The still- hot glass is placed in the oven and heated to a temperature at which the glass is rigid enough to keep its overall shape, but plastic enough to flow so as to relieve internal strain. It is then cooled slowly to room temperature. Even though strains develop after the glass cools, or “sets”, these strains are never severe enough to crack the glass.
Polarized Plates
Strain-free Seal
Strain lines show as light band in polarized light
Another method of cutting glass is by applying a hot rod to the scored tube. This is done in the following manner:
Make a deep scratch on the tube as described above. Hold the tube in one hand and with the other hand, take a piece of 3mm rod and soften the end in the torch. When the end of the rod is molten, touch it to the scratch. If the scratch is straight, the tube will break cleanly. (See Figure 5) This method is convenient to use when the apparatus prevents you from grasping the tube in both hands.
Procedure for Rotating Tubing
Uniform rotation of glass during heating and blowing is essential for obtaining an evenly distributed wall thickness. The process of rotating cannot be overemphasized! If you stop rotating while your work is in the flame, it will sag or thicken on one side. Only by continuous, even rotation can you get smooth, even seals. You may rotate in any direction, but it is most common to have the top of the glass move away from the glassblower.
The tubing in the left hand should be supported by the last three fingers, which act as a bearing. The thumb and forefinger are then used to rotate the tubing.
Wet File Mark
Figure 5
The tubing in the right hand is held differently. The right palm faces up and the tube is held between the forefinger and the thumb. The other fingers are arranged so that at least one is under the tube and is ready to support it when the finger and thumb release their hold and take a new hold on the tube. This is the hand that will give the beginning student the most trouble. Practice the right hand rotation as much as possible.
You must synchronize the right and left-hand movements to prevent twisting of the tubing in the heated zone. This may be practiced by joining a pair of tubes with a piece of cloth, and then rotating the tubes without twisting the cloth.
Left Hand
Figure 6
Right Hand
Figure 7
Figure 8
Basic Glassblowing Seals
The following seals will be discussed and practiced by each student:
- Fire polish tube ends
- Pull points
- Round bottoms
- Flat bottoms
- Butt seals
- Flare tubing
- “T” seals
- Tubing bends
- Rod seals
- Blind seals
- Capillary seals
- Blowing Bulbs
Included in the basic seals portion will be construction of the following:
- Eye droppers
- Volumetric pipettes
- Glass flower
- Graduated cylinder
- Bulb to bulb distillation apparatus
- Migratory fowl barometer
Lesson 1: Fire polish tube ends
Fire polishing the sharp ends of the glassware is a very important procedure. The glassblower is constantly blowing into the open ends of the apparatus and a sharp edge can cut the lips very severely. For your own safety, fire polish all sharp edges before beginning to heat the apparatus.
Fire polishing is accomplished by rotating the glass in the flame near the outer edge. Heat the glass until the edges flow into the hemisphere shape on the end. Do not heat to the point of constricting the diameter of the tube. Flame anneal each seal.
Fire Polish
Lesson 2: Pulling points
“Points”, as designated by glassblowers, are elongation’s on the ends of tubing, formed by pulling the tube to a small diameter. They form convenient handles for holding short pieces of tubing, as well as providing a means for closing the tube.
The correct procedure in pulling a “point” consists of rotating the tube in the flame so as to heat a length of about 2 times the diameter. When the glass has become pliable, remove it from the flame, and while still rotating, pull slowly to a length of about 4-5”. It is important that the resulting “points” have the same axis as the original tube. If the “points” are not in line, it will be necessary to heat at the junction with the tube to straighten them. Flame anneal each seal.
Lesson 3: Round Bottoms
The round bottom is made using one of the “points” that you have just made. Place the large diameter in your left hand and the “point” in your right hand. (Refer to tubing rotation section.) Next, heat the junction of the “point” in the flame and slowly draw it away. Burn the “point” through in the flame and remove it. Now, with the tube end sealed, rotate down and into the flame to gather the glass. The glass will thicken as you are heating. After sufficient heating, and while still rotating, remove it from the flame. Turn the end of the tube up and blow lightly into the open end of the tube. Blow just hard enough to shape the molten glass into a hemisphere on the end of the tube. Repeat this procedure until the round bottom is formed. The glass in the bottom of the seal should have the same wall thickness as the starting tube. If your round bottom is not uniform, your rotation in the flame was not even and smooth. Flame anneal each seal.
Heat 2 times the diameter
Draw
Burn Through
Rotate!
Lesson 5a: Butt Seals
Uniform butt seals require even rotation of the glass with both hands. (Refer to Tubing Rotation Section.) Cut two tubes of the same diameter to a 6” length and put a cork stopper in the end of one tube. Place the stoppered tube in the left hand and the open tube into the right hand. In a narrow flame, begin heating both edges until they begin to flow. While continuously rotating, remove the tubes from the flame and touch the back edges together and roll the tubes together. While the seal is still molten, blow lightly into the open end. Move back into the flame and reheat the seal until the edges begin to flow and gather thickness. Again, remove the glass from the flame while rotating, and blow into the open end. Blow the seal up slightly larger than the diameter of the starting tubes. Repeat the heating process, but this time blow the seal up to the same diameter as the starting tube. Rotate the seal to straighten. Flame anneal each seal.
Pre-heat edges
Touch edges and roll together
Blow
Heat to fuse seal
Blow
Complete
Rotate!
Lesson 5b: Butt Seals with Different Sized Tubes
Butt seals on large diameter to smaller diameter tubing is quite a bit trickier than same size seals. First, cut and fire polish a 4” piece of 9mm and an 8” piece of 22mm. Then, you start by pulling a point at the middle mark on a piece of larger tubing. Next, remove the handle as if you were making a round bottom. You then blow out a small hole in the end of the 22mm that is about 9mm around. (Just the same size as the small tube.) Cork the 22mm tubing and rotate it in your left hand, and rotate the 9mm in your right hand. Heat both edges so they begin to flow, bring the glass out of the flame, attach the tubes together, and blow lightly. You may have to go back in and rework the seal a few times. Each time, heat directly on the seal, remove glass from the flame, and blow. Always remember to ROTATE!! Flame anneal each seal.
Pull a point, and remove the handle here
Rotate! Blow 9mm hole in end of tube
Attach the tubes, and work all sharp edges out of the seal.
Lesson 6: Flare Tubing
To begin flaring tubes, cut and polish 9mm tubing into 6” lengths. Hold the 9mm tubing in your left hand, and in your right hand, hold the graphite rod (found in your toolbox). The first of the flares will be a 45° flare. With a large flame, begin rotating the tubing in the flame. You will want to heat about 2 times the diameter of the tubing in order for the flare to be thick enough. Once the glass is hot, remove the tube from the flame, and insert the graphite rod into the tube. You should insert the rod far enough into the tube so that the far edge of the rod is resting on the cool part of the glass. In order for the edge to stay hot enough, you will want to keep the outer edge of the flare in the flame. Continue to rotate the glass, while bringing the graphite rod to about 45° angle. Completely remove the glass from the flame. Continue to rotate the glass against the rod until it completely cools. Flame anneal.
Lesson 7: “T” Seals
To begin the same size “T” Seals, cut and polish 9mm tubing into 8” (cut at 8”, and mark at 4”) and 4” lengths. With the corked 8” piece in your left hand, come up from underneath the small flame at the 4” mark. Heat a small area on the side of the tube until molten, and then blow lightly to form a small bump. This bump should be about 9mm. Heat the top of the bump in the flame until it becomes molten, and then blow out the glass. There now should be a hole about the size of the tube to attach to it (9mm). (If your hole is too small, you can use the graphite rod to push out a bigger hole.) Next, cork the other end of the 8” piece of tubing. Hold this in your left hand. You should come up from underneath of the flame with this tube, and hold the other tube in your right hand. Then, get all edges molten, come out of the flame, and stick them together. To get a good seal, you may want to stick the back edge together first and roll them together. Then, in order to get a nice, strong seal, the cold edges must be worked. At this point, you will want to get the smallest flame you can. You then can begin by picking one spot of the seal, and begin “spot heating” around until all of the sharp edges are gone. You can do the large to small “T” seals following all of the steps mentioned above, using an 8” piece of 22mm. Flame anneal each seal.
Blow out 8mm hole in middle of tube
Come from underneath the flame
Spot heat at the seal to work out all rough edges
Complete
Lesson 8: Tubing Bends
To begin, cut and polish 9mm tubing into 8” (4x) and 12” (4x) pieces. When bending tubing, it is important that you get enough of the tubing hot enough, so you don’t have to rework your bends. A good rule of thumb is to heat 3 times the diameter of the tubing for the 90° bends, and to heat about 4 times the diameter of the tubing for 180° bends. Begin by adjusting your flame to be the biggest, hottest flame you can get. Then, with the corked end of tubing in your left hand, begin rotating the tube in the flame, heating back and forth. Remember to heat about 3 times the diameter. So, for 9mm tubing, try to heat about 27mm (or just over 1”). Once you have the glass just to the softening point, you then want to sweep the backside of the tubing into the flame. (This will allow the outer side of the bend to be hot enough to blow out round.) In order to do this sweeping motion, you will need to move your left hand to hold the tube from the underneath (like the right hand holds the tube). This will also allow you to smoothly bring the tube up to your mouth to blow. After you sweep the backside, bring your right hand up to your mouth, bend the tube up 90°with your left hand, and blow. If the tube is heated correctly, you will not have to rework the bend. Sometimes, it may be necessary to use a small flame on the inside of the bend to work out any kinks. Flame anneal.
Heat 3 times the diameter of the tube Swipe backside of tube into flame.
Bend at 90° angle, while blowing into the right side. Work out any folds on inside of bend with small flame. Flame anneal.
