It is difficult to think about when a glass was not a part of our every day lives, but for hundreds of years, glassmaking techniques have been a guarded secret which still is. Here is some information on these guarded secrets as well as how the people that work with glass bring this common material to life in various art forms.
There are various glass types, yet the more common type used for art is known as soda-lime glass which often goes by the name of "Soft Glass," while borosilicate glass is known as "Hard Glass." The soda-lime glass is the more widely used type which is used as the standard for glass containers and standard windowpanes.
The borosilicate glass is classified as a type of specialty glass, which is primarily used in glass-blowing processes which is called lampworking. This glass has a much higher melting point compared to soda-lime glass. Even though it is more complex to make compared to traditional glass, its physical strength and refractory properties have made it the preferred choice for laboratory equipment of high-durability like test tubes, beakers along with the items that are more common like telescope mirrors and cookware.
There are a number of different ways and techniques when it comes to working with either of these glass types to produce two-dimensional artworks, jewelry or sculptures. The approaches include: cold working that involves working at room temperature with the glass, fusing glass, glass casting, lampworking, stained glass and glass-blowing.
About Glass Blowing
Glassblowing which is also known as "Hot Glass," involves the process of working with a soft glass. The technique involves 3 furnaces, along with a specialized blowpipe which is dipped into a furnace that contains a crucible of molten-glass at a temperature of around 2000 °F. The molten glass is then collected onto the blow-pipe in a similar method to how honey is gathered onto a dipper.
The artist is then able to manipulate this glass into the desired base shape, followed by inflating it into a type of vessel. If a piece requires reheating between the different steps, the artist uses a 2nd furnace known as the "glory hole." The last furnace is known as the annealer or kiln, that is used for gradually cooling the glass. This prevents cracking in the glass caused by thermal stress. These techniques are commonly used for making medium onto larger artworks along with the functional pieces such as sinks, bowls and vases.
Glass Casting
Glass casting involves techniques of using soft glass in a furnace, inside a kiln or on a special torch. In general, the artist will make their mold from silica, plaster or refractory sand. The mold is then filled with colored, patterned or clear glass, dependent on the effects and techniques desired. The larger scale sculptures are typically created in this way.
Lamp Working
This is a term that describes glass which is heated and then manipulated with the use of an oxygen or propane torch. These are torches which have the ability to reach temperatures of up to 5300 degrees Fahrenheit. With lamp working the artist will usually work from a bench with the use of glass tubes and rods, and shaping with various graphite and metal tools, with gravity as the more important tool. With this technique, the artist is limited when it comes to the size of the end product, but an increased detail level is easier to achieve with this method.
Annealing
This technique is done inside a kiln and when it comes to glass, it involves heating the piece until the temperature of the glass reaches what is known as a stress-relief point. This means that the glass will still be hard enough that it won't deform, yet soft enough that the internal stresses start to ease up. The glass is then able to heat-soak until the temperature is consistent throughout.
The time-frame for this process will depend on the glass type and its thickness at the piece's thickest section. The piece of glass will then be gradually cooled to the predetermined rate, until the temperature goes below the critical point, where it will not generate any internal stresses, and is then able to drop to room temperature. The blown glass art which was not annealed might shatter or crack due to even a minor change in temperature or other types of shock.