Views: 122

GLASS BLOWING

1. List four glassware used for measuring liquids in the laboratory.
   • Graduated cylinders,
   • Pipets,
   • Burets
   • Volumetric flasks.
2. Distinguish between the soft glass and hard glass.
   1. Soda glass or soft glass

• Soda glass melts on a Bunsen burner flame.
• They are very cheap and readily available in any quantity and size.
• Give an intense and persistence yellow sodium flame on heating.
• They are smooth on feeling with finger i.e. the edges will feel smooth on scratching.
• When viewed against a source of light, its edge will have a green tinge.
  1. Hard glass (Borosilicate
• Is a hard colorless glass with a low coefficient of expansion it softens at high temperatures
• Can be put to the flame directly  and requires  less  annealing than soda glass
• They are  rough on feeling  or the edge will feel  rough on scratching
• It’s expensive than soda glass

3. Describe the formation of bloom on glass

A bloom is a ring formed on a glass product about 3mm from the point of heating because of sodium ions in the glass coming into contact with sulfur ions in the glass

There are two types of blooms

(a)Temporary bloom

These can be wiped out on cooling

(b)Permanent bloom

This is only removed by chemical means

4. Explain how a bloom can be removed from glass.

Depending on whether it is a temporary or permanent bloom, blooms can be removed by simply wiping out on cooling (temporary bloom) or removed by chemical means (permanent bloom)

5. Define the  term  devitrification

Devitrification is a, process by which glassy substances change their structure into that of crystalline solids .Devitrification occurs in glass art during the firing process of fused glass whereby the surface of the glass develops a whitish scum, crazing, or wrinkles instead of a smooth glossy shine, as the molecules in the glass change their structure into that of crystalline solids.

6. Describe the cause of devitrified glass and how it can be removed.
   • Devitrification is the process of formation of crystals in glass (crystallization of glass).
   • Devitrified glass looks or appears translucent; it is rough and cannot be seen through easily .Its cause by;
   • Heating of a piece of glass on a hot flame for a very long time.

(ii) Heating a piece of glass and then suddenly introducing it to a cool condition     (rapid cooling of glass)

1. Chemical weathering  (due to old age ) , the moisture collects  on glass and when  it combines  with atmospheric CO₂, it forms carbonic acid  which eats up the soft  sodium ions  of the glass  and the hard ions  becomes crystallized  or crystallizing on the surface  of the glass

7. Devitrification can be eradicated by:

Pouring strong solution of NaOH on the glass surface and leaving it on for some time. These will etch up the ends of the glass that are sticking out and a smooth glass will be produced.

NB this process may however result in the formation of thin glass.

By fusion – in these case the piece of glass is put in an oven until it softens out so that the crystals ticking out of the glass will be  fussed into  the walls of the glass .These method is not suitable for  volumetric glassware , because when they are heated to high temperatures , they don’t regain  their original size  on cooling .

8. Explain the importance of annealing process and how it is done.

Annealing is the process of removal of strains from a fixed glass product   it is a process of cooling down of the glass from its annealing temperature in a slow, gradual, and stepwise manner until the room temperature is reached.

9. State the uses of the following laboratory wares

Desiccators

This is a large glass vessel with a tightly fitting cover in which the atmosphere is kept free of moisture by use of a drying agent called desiccant placed in the lower chamber or compartment

Used for  holding hot crucibles after it is heated  so as to protect it and its content  from contact with moisture. Between the glass cover and   ground glass rim is coated with Vaseline or grease to avoid air getting in

When using the desiccator, carry it using both hand and place on the table and hold firmly with your left hand. Hold the knob of the cover with your right hand and pull it aside by sliding it away.

Do not keep the cover on the table but hold it in your left hand facing upside down in order to avoid dirt getting in contact with the grease

Place the hot crucible in the desiccator using a pair of tong. Slide the rim of the desiccator until the rims closes completely. Do not place the red hot crucible in a desiccator but allow to at least cool.

Winchester bottles

Used to hold and store definite volumes of solutions in the lab

Clay triangle

They are used for supporting the crucibles on a retort stand while heating it on a Bunsen burner or while placing it in the desiccator for drying .it is formed by passing three pieces of glass through small length of heat resistant clay tubes, the wire is then twisted at the end to form a triangle.

Wire gauze

Used to spread heat of a burner flame

             Crucible tongs

Used to hold the crucible

10. Give examples of glass wares that fall into the following classifications
    1. General-purpose glassware

These glassware are not calibrated. They are used for various jobs that do not require measurements e.g. test tubes, beakers, flasks etc.

1. Special purpose glassware

They are designed to perform only specific jobs e.g. density bottles, condensers etc.

1. Standard, jointed, or quick fit glass wares

They are glassware with interchangeable ground joints e.g. distilling flask, soxhlet extractor’s etc. they are suitable for general use in preparative organic chemistry

1. Volumetric glassware

They include burettes, volumetric flasks, and pipettes. They are graduated either to deliver or to contain a specified volume i.e. EX – to deliver and   IN – to contain.

The temperature of calibration is also shown is also shown on the glassware (usually 20 ^o c).

Volumetric glassware are either classified as class A or class B Class A have a tolerance of + or – 0.001 cm³ at the stated temperature while class B have a tolerance of 0.010 cm³ at the stated temperature

11. Describe each of the following techniques used in glass blowing

Fire polishing

Fire polishing is the process of smoothening a glass rod after cutting

               Glass bending

The process of heating soft glass to enable folding or bending into different shapes and angles.

Describe how to make a Y bend using a glass tubing

The Y tube is made in a similar way but the tube is first bent to the desired angle. The other bulb is then attached in the manner described above. All such junctions should be carefully annealed. Y joints are used for sharing services in the laboratory e.g. gas and water.

12. Describe how a very thin capillary tube can be made from a glass of a larger diameter

The larger diameter tubing is sealed at one end with a rubber tubing and the other end is rotated in the flame until the bore is the same diameter as that of the smaller tube. One end of the smaller tube is then gently heated and the two hot ends are joined together. The flame is introduced and the junction is rotated over it.

When red hot, the tubing is removed and the free end is gently blown to form a small bulb at the junction. The process is repeated until the two tubes are fused together, but when fusion is complete, the two tubes are pulled slightly apart to cause slight tempering at the junction.

13. Describe how center bulb is made in glass blowing.

On end of the tubing is stoppered and heat is subjected at the middle of the tubing until it is soft and red. Remove it from the flame and press both ends towards the center to form a ring. Heat the ring formed until its red-hot and blow. Repeat the process until the bulb formed reaches the required size.

14. Outline the procedure for making Pasteur  pipette in the laboratory

Pasteur used long thin glass tubes cut into appropriate lengths. The ends were plugged with cotton wool to prevent any contaminants from entering. The centre of the tube was then heated until molten and quickly pulled apart to make a long and very thin tube between the larger ends. The tube was then snapped in half to create two fine tipped pipettes.

15. Explain” weathering” as used in glass blowing

A glass container may sometimes be affected by a phenomenon is known as “weathering” or “blooming” and occurs due to the presence of water on the glass surface. This is usually through the cycling of condensation and evaporation and can lead to the formation of deposits on the glass surface.

How does Blooming or Weathering happen?

The processes involved are typically as follows. Glass in storage is wetted by condensation, which usually forms due to a drop in temperature. The most common cause of temperature variation is the daily cycle of temperature from day to night. However, similar variations can occur due to transportation as well as storage.

This condensation leaches out alkali ions (sodium and/or potassium) from the glass leading to the formation of an alkaline solution. As the temperature rises throughout the day the liquid evaporates and leaves a more concentrated alkali solution. Eventually, all the liquid evaporates from the surface leaving alkali salts on the glass surface. These are usually in the form of carbonates from the reaction with atmospheric carbon dioxide.

What can be done to help prevent Blooming or Weathering on Glass Containers?

Factors that can affect the severity of this reaction are the humidity and temperature stability of the storage area, the packaging of the pallets and local weather conditions. While there are no set times for storage in any environment before the onset of weathering, this is an effect that normally occurs only after extended periods of storage under adverse conditions. Ideal storage conditions would be dry, well ventilated areas with a relatively constant temperature and low humidity.

16. Explain how to store glass tubing and rods of various sizes in the laboratory.

By first wrapping them together and placing them a box of appropriate length them keeping them in a shelf that can accommodate their length

17. Explain why laboratory glassware made up of borosilicate are more common than those made of soda lime

Because borosilicate glassware is highly resistant to heat, hence do not melt easily.

They also have high mechanical strength i.e. they do not beak easily, fairly inert to chemical   have high resistance to thermal shock, high melting point and softening point. They are used for making beakers, flasks and most laboratory apparatus

18. Explain why glassware made of hardened glass such as Pyrex has long chemical durability

They also have high mechanical strength i.e. they do not beak easily, fairly inert to chemical   have high resistance to thermal shock, high melting point and softening point.

19. Outline the procedure of joining glass tubes of equal diameter in a glass blowing laboratory.

To join two tubing together, one end of one tube is stoppered and one end of each tubing is gently heated. They are then both removed from the flame and the two heated ends are slightly pressed into each other. The flame is reduced, and the junction is carefully rotated over it.

When red hot, the tubing is removed from the flame and the free end gently blown to form a small bulb at the junction

The process is repeated until   when the two tubing are fussed together and the line of junction has disappeared. It’s then bowed and gently cooled until the bore is of uniform diameter

20. Give the uses of the following items in a glass blowing room

A triangular file

Used for polishing the ends of the glass tubing, for making a nick or to effect a mark on a glass tubing

Annealing oven

Used for removing strains in glass

21. Outline briefly the main features of glassblowing room

A glass blower’s workplace can range from a small one or two-person shop to a large, industrial building.

Since glass making requires three furnaces (a furnace, a crucible, and the annealer), space is often at a premium in small studios. Work areas include the long, flat marver surfaces, often aligned at a height that allows the worker to stand as they roll and shape the glass.

Glass blowing is hot, potentially dangerous work. A glass blower needs a high tolerance to heat, manual dexterity and the patience to work the molten glass using a step-by-step process. Safety is an important consideration in glass blowing workplaces, as burns from molten glass can be severe and debilitating.

22. State the use of each of the following glass blowing tools

Glassblowing is a glass-forming technique that involves inflating and shaping hot glass into a variety of objects such as art pieces, drinkware, and glass containers. Glassblowing is an important form of art and is vital in the making of glassware used in a variety of industries, such as the laboratory sciences.

Glassblowing takes years of practice and dedication to master, as well as specialized tools and equipment. Below is a comprehensive list of the tools glassblowers use to make the many products found on the market today.

Large Equipment Used in Glassblowing

There are several key pieces of large equipment used in glassblowing studios: furnaces/glory holes, annealers, benches, and yokes. These items are essential to the glassblowing process and serve important functions from the start of a project to the end

• Furnace/Glory Hole

Most glassblowers rely on furnaces as their sources of heat. Furnaces used today are typically gas-powered and reach temperatures of 2,000 degrees Fahrenheit. Each furnace has a glory hole, an opening in the furnace where glass is gathered and reheated.  

Benchs

The bench is the place where a glassblower performs much of his or her work. Benches are usually made of a mix of wood and metal. Benches have arms to support the blowpipe and glass project and hold the other small tools glassblowers use through the glass making process.

Yokes

A yoke is a stand that is placed in front of a glassblower’s furnace to support pipes as they enter the glory hole. The pipe is set on the yoke to keep it steady and guide it into the furnace to gather glass.

Annealer

An annealer slowly cools a finished glass product so it does not shatter. The annealer creates a controlled environment in which the glass can very slowly cool and harden to room temperature. Without the annealer, glass would cool too quickly and break. Annealers can be compared to kilns used by pottery artists.

Small Equipment Used in Glassblowing

Blocks

A block is a wooden tool used for shaping gathers of glass. After a glassblower gathers hot glass from the glory hole, he or she takes the glass over to a bench to begin working it. Blocks are soaked in water to create a layer of steam when in contact with hot glass. They help form glass into a rounded, even shape to prepare it for inflating and further shaping.

Blowpipe

Blowpipes are used to blow air into glass and inflate it. Used during the beginning and middle stages of the glassblowing process, blowpipes are hollow and metal with a mouthpiece on one end and a place for hot glass to gather at the other.

Torches

Torches are the equivalent of furnaces for lampworkers, but can also be used in glassblowing while moulding the workpiece.

In terms of lampworking, because they work on a much smaller scale, lampworkers rely on the heat of torches to soften and shape glass. While any torch technically works for lampworking projects, serious artisans use torches specifically made for glassworking. These torches have more precise flames and heat to the appropriate temperatures.

Jacks

Jacks are a pair of metal blades held together at the end with a curved handle. They look like large tweezers and are used to shape glass as it is rotated at the workbench. Jacks can be used to shape glass as it is being inflated, separate glass from the blowpipe towards the end of the work process, and widen the opening of glass vessels.

Shears

Shears are used to cut or constrict hot glass. They come in two types: straight and diamond. Depending on the type of project being completed, glassblowers will favor one over the other.

Paddles

Made from wood with a handle at the end, paddles are used to form the bottom or other flat edges of glass pieces. The glass is carefully pressed onto the paddle to create a flat surface.

Molds

Molds are used to shape glass into preset shapes and items. Molds are generally made from brass or wood and can be custom made to suit the needs of individual glassblowing projects.

Crimps

A crimp is a metal device that looks a bit like a pair of kitchen tongs, but has a textured surface. This tool creates a decorative design and texture when glass is squeezed between it. Crimps come in a variety of sizes, with different patterns to suit your specific needs.

Marvers

A marver is a table or surface on which glassblowers shape hot glass. Marvers are made from steel, brass, or graphite and were originally made from marble, which is how they got their name.

Parchoffi

A parchoffi is similar to the jacks discussed above, but they have wooden blades instead of metal ones. Wooden blades are more rounded and therefore do not leave any marks in the glass when used to flare or shape the opening of a vessel. A parchoffi is dipped in water prior to using it to help it glide across the surface of the glass.

Punty

Used after glass has been inflated, a punty is a small metal rod that glassblowers transfer their work to in the finishing stages of the glassblowing process. The punty is carefully attached to the bottom of an inflated glass piece so the glassblower can work on the top of the item.

Pyrometer

A pyrometer is a remote-sensing thermometer that records the temperature of annealers and furnaces. This tool is helpful in ensuring that glass is heated and cooled down properly.

Safety Glasses

Wearing high-quality safety glasses is extremely important when glassblowing. The work environment is dangerous due to the amount of heat and delicate glass being used. Some risks to glassblowers’ eyes include: shattered glass, sodium flares from the heating compounds found in glass, UV light, and infrared light.

Proper safety glasses protect the eyes from these dangers and allow glassblowers to see their work properly despite strong light.

Soffietta

If a glassblower needs to inflate a piece more after it has been taken off a blowpipe, he or she can do so using a soffietta. This tool features a metal tube with a conical nozzle at the end. The cone is placed at the opening of th glass and air is blown through the tube to further inflate the glass.

Taglia

A taglia is a steel knife with a squared-off end that is used to shape molten glass. Taglias can be purchased with sharp or rounded edges depending on the needs of the glassblower.

Tweezers

The tweezers used by glassblowers look like household ones, but they are much larger and are used to transfer glass to the punty rod

 

23. State the use of the following tools in a glass blowing laboratory

• Puffer
• Paddles

 

24. State three methods of cutting glass.
    1. Glass Cutter

• This is probably the most common way to cut glass. A marker pen is used to mark the cut, and a straight edge – such as a ruler – is used to guide the cutter over the glass. The correct technique involves making long, continuous movements with the cutter, ideally from one side to the other in one sweep.
• Don’t go back over spots that you have missed, make another whole sweep instead. You should be able to grab the glass with two hands, and force it apart to break it. The cut should be clean, but may need a rub down with sandpaper.
  1. Shaping Glass
• If you have a large sheet of glass that you need to reduce in size before measuring a window, you can shape and cut glass down by submerging it into cold water, and cutting it while it is under the water. Regular scissors (although a big pair will make the job easier) can be used to roughly cut the glass down to size.
• You will need to use a water tray that is fairly large and deep enough to hold the glass under the surface of the water as you work on it. The glass can be cut as soon as you submerge it, and can be safely used as soon as you finish cutting.
• Also, this method will leave the cut edge of the glass quite rough; take care when handling it. The science behind this trick is very simple; the water cancels out any vibrations that would normally crack the glass as you cut.
  1. Clean Cut With A Wire
• To get a clean cut without a glass cutter, the easiest method is to use a length of thin wire. You will also need a wide and a deep water container, big enough to allow you to plunge the sheet of glass into. Fill the container with cold water. Mark the glass with a pen, and then use a sharp implement to make a score mark along the maker. Make the score mark deep enough so that you can place the wire into it.
• Feed the wire into the score mark and remember to leave some excess wire at one end. Next, heat this excess wire, so that the whole of the wire heats up and becomes red hot. After around half a minute, plunge the glass into the water and then use a soft headed mallet to knock the glass. It should break off cleanly.

NB/ Always make sure you have eye protection and work gloves on when cutting glass.