ASSIGNMENT PART A
READ TOGETHER IN CLASS + TAKE NOTES
Glass...has a random molecular structure, whether the glass is cold or hot. It is often called a “super-cooled liquid” because, at room temperature, it seems to be a solid, but it has the random molecular structure of a liquid.
When, for example, metal is heated to a specific temperature, a phase change occurs. Its orderly molecular structure—crystalline—becomes random. This is the melting point, at which a solid becomes a liquid. Glass does not behave in this way. It has a random molecular structure, whether the glass is cold or hot. It is often called a “super-cooled liquid” because, at room temperature, it seems to be a solid, but it has the random molecular structure of a liquid. Odd, no? Thus, speaking practically (everything in this chapter could be described in this way because I am a glassblower and not a scientist), glass has no melting point; as it gets hotter, there is never a phase change. As glass is heated, it does something much more interesting than melting: its resistance to flow (viscosity) gradually diminishes as the temperature increases. (The temperature range in which glassblowing processes typically take place is roughly 1,300–2,100 degrees Fahrenheit [700–1,150 degrees Celsius]). At these temperatures, glass is in a “plastic” state; that is, it can be shaped easily. “Malleable” is another word used to describe its curious softness. In this state, molten glass can be stretched easily (Vid. 1).
In fact, at the most fundamental level, glassblowing is a way of stretching glass. Just as, say, tweezers can be used to pull a mass of glass to become long and narrow, compressed air can be introduced into the center of a molten mass to create and expand a bubble. The soft glass is stretched outward in all directions (Vid. 2).
This brings us to the second physical property required for glassblowing. Glass is a poor conductor of heat, compared with any metal. For glassblowing to work, the glass, as it is inflated, must hold its shape. It does so because, as the bubble grows in size, the outer surface cools rapidly and stiffens somewhat. Because glass is a poor conductor, the greater heat beneath the outer surface only slowly “replenishes” the heat at the surface. The soft bubble of glass can therefore increase in size while maintaining its form. This could not happen with metal because its greater heat conductivity would prevent the outer-wall/inner-wall heat differential required for an inflation process. In addition, as we have seen, metal exists as either a solid or a liquid. It never exhibits the “in-between” plastic state of hot glass that allows the stretching required for glassblowing.
You can learn more about the history of glass blowing and ancient forming techniques here: https://romanglassblowing.cmog.org/05-Ch01-Glassblowing-Its-Basic-Principle-Early-Processes/
Lampworking is a type of glasswork where a torch or lamp is primarily used to melt the glass. Once in a molten state, the glass is formed by blowing and shaping with tools and hand movements. It is also known as flameworking or torchworking, as the modern practice no longer uses oil-fueled lamps.
The technology for glass beadmaking is among the oldest human arts, dating back 3,000 years. Glass beads have been dated back to at least Roman times. Perhaps the earliest glass-like beads were Egyptian faience beads, a form of clay bead with a self-forming vitreous coating. Glass beads are significant in archaeology because the presence of glass beads often indicate that there was trade and that the beadmaking technology was being spread. In addition, the composition of the glass beads could be analyzed and help archaeologists understand the sources of the beads.
Wound glass beads
Probably the earliest beads of true glass were made by the winding method. Glass at a temperature high enough to make it workable, or "ductile", is laid down or wound around a steel wire or mandrel coated in a clay slip called "bead release." The wound bead, while still hot, may be further shaped by manipulating with graphite, wood, stainless steel, brass, tungsten or marble tools and paddles. This process is called marvering, originating from the French word "marbrer" which translates to "marble". It can also be pressed into a mold in its molten state. While still hot, or after re-heating, the surface of the bead may be decorated with fine rods of colored glass called stringers. These are a type of lampwork beads.
Source: https://en.wikipedia.org/wiki/Glass_beadmaking
Safety: According to the International Society of Glass Beadmakers, which referenced a recent NIOSH report the reasons to use didymium safety glasses are:
1. they help protect the eyes from flying glass shards
2. they help protect the eyes from radiation (IR, and with borosilicate - UV)
3. they help to filter out the flare of the molten glass so that you can actually see what you’re doing
[Didymium (Greek: twin element) is a mixture of the elements praseodymium and neodymium. It is used in safety glasses for glassblowing and blacksmithing, especially when a gas (propane) powered forge is used, where it provides a filter which selectively blocks the yellowish light at 589 nm emitted by the hot sodium in the glass, without having a detrimental effect on general vision]
NEVER STARE AT THE FLAME WITHOUT DIDYMIUM SAFETY GLASSES!
We are using a Hothead torch attached to Mapp gas (propylene). Be sure to turn the gas off securely every time you are finished. Always tie your hair back and do not wear loose clothing - you should wear long sleeved, cotton or natural fiber clothing and no shorts, plunging necklines or open toed sandals… just in case. Long artificial nails can sometimes pose a hazard for beginners. Always be aware of your surroundings. Do not light your torch with someone standing in front of your desk. Make sure there are no flammable materials on the desk. Assume everything at a heat station is hot.
ANNEALING EXPLAINED
Annealing
Annealing is a term used in both metal and glass industries. When you heat glass, it expands and as it cools it contracts. This sets up stresses between the interior and the surface of the glass and if the glass cools too quickly it can cause thermal shock - or breaking.
When you anneal an object you are slowly raising the object in temperature to just beyond it’s “stress point” – which is a type of melt point that removes any internal stresses within the object. The idea is to hold (or flame soak) the object at just beyond this stress point for a period of time to remove any pressure inside the object. Then the item is left to cool down very slowly and this action will strengthen the object and provide it with long term durability.
Flame annealing is the technique of heating the bead at the end of your flame (increasing the propane slightly for a hotter flame) until it is lightly glowing red to remove any stress put into the bead. In flame annealing, you will rotate the bead out of the flame until it loses it’s glow and then place it in a fibre blanket or vermiculite to cool down slowly.
Want to know more?
Assignment Part B:
Make a symmetrical glass bead. Present the bead on a bracelet, necklace or other application. If you want to create a more sophisticated bead you may as soon as everyone has had a chance to make a simple bead.
Art + Science of Materials Glass Bead Rubric
15 pts
Artwork and Studio Habits reflect students ability to:
________ 5) Studio Habits
________ 5) Create a symmetrically shaped glass bead.
________5) Employ good craftsmanship – smooth edges, presentation that enhances / showcases bead.
0 not observed 1 limited 2 emerging 3 basic 4 skilled 5 accomplished