Studio Art Glass
Glass is an amorphous solid (non-crystalline) material. Most of the studio glasses used today are referred to as soda-lime glass composed of approximately 70% silicon dioxide (silica), sodium oxide, sodium carbonate (soda ash), and calcium oxide (lime). Metal oxides make the colors in glass: gold, copper, tin, chromium, cobalt, silver, cadmium, manganese Etc. Hot glass can be formed into almost any shape. Glass can be poured, formed, blown, cast, extruded and molded into forms ranging from flat sheets to highly intricate shapes.
Common Glass Art Techniques
To create a blown glass object, the molten glass is "gathered" from the furnace on the end of a long hollow metal "blowpipe". At this stage the glass is typically heated to around 2100 F degrees, and has the consistency of honey (it "freezes" at around 900 F degrees). The glassblower introduces air into the center of the gather through the blowpipe. A variety of tools as well as gravity are then used to shape the glass into a form. As the glass cools it begins to stiffen and must be reheated to allow continuous shaping and reshaping. A smaller furnace, known as the "glory hole" (because of its bright glow) is used for the re-heats, which allow pieces to be worked-on for extend periods of time.
When the piece is finished being shaped, it is placed in an oven (kiln or lehr) for annealing. Annealing is the processes of stabilizing the glass form at the temperature in which it has stopped moving, but still soft enough for the stresses to relax, typically in the 900 F degrees range for most studio glasses. Uneven temperatures within the structure of heated glass causes stress and can result in cracking during the cooling, or even after a period of being at room temperature! The thickness of the glass and the thermal expansion coefficient determines the length of time the glass needs to anneal. Thicker pieces need a longer annealing cycle than thinner pieces. After “soaking” at its annealing temperature to remove internal stress, the kiln can begin its cooling down cycle. This process occurs very slowly, lasting anywhere from overnight to weeks! Annealing is utilized for any types of glass that requires being heated.
Denotes a technique in which glass is gathered from the furnace on the end of a solid metal rod and shaped with tools and gravity into a sculpture. Although the set up is essentially similar to that for blown glass, no actual blowing takes place.
Cast Glass (Hot Casting):
Entails molten glass, heated to a temperature of up to 2200F degrees, scooped from the furnace with a large ladle and poured into a mold where it solidifies. The technique has been used since the Egyptian period. Modern cast glass is formed by a variety of processes such as kiln-casting, or casting into sand, graphite or metal molds.
The object to be cast is modeled in wax and encased in a ceramic or plaster mold. The mold is heated and wax flows out; powdered or molten glass is poured in, and fired until the glass becomes fused or molten. Then it is annealed for an extended cycle due to the thickness of the ceramic/plaster and encased glass form. When finally at room temperature, the encasement is carefully removed and the glass is chased and cleaned.
Pâte de Verre:
Literally translated means glass paste. Finely crushed glass is mixed with a binding material making a paste. The resultant paste is applied to the inner surface of a negative mold forming a coating. After the coated mold is fired at the appropriate temperature, the glass is fused creating a hollow object that can have thick or thin walls depending on the thickness of the pate de verre layers.
Is an ancient technique still in use today. It involves creating a mold by depressing objects into damp silica sand, (which is mixed with a binder like bentonite or injected with C02 to make it hard), and molten glass is then poured into the mold.
Kiln-formed Fused Glass:
Thin sheets of glass are stacked and assembled, often using different colors, glass stringers, or frit (crushed colored glass) to create patterns or simple images. When slowly heated in a kiln, the glasses start to soften, and begin to bond together. Depending on the temperature and timing, the glass will 'tack' together and have texture and depth. At higher temperatures the glass will melt together more thoroughly and fuse flat with rounded edges.
In Slumping, the glass is laid into, or on top of a mold of plaster, metal or ceramic and heated just to the point where it softens or "slumps" to fit the form of the mold using gravity. Once the glass softens to the desired shape, it must then be quickly cooled to annealing temperature to stop the movement.
Lampworking Glass (AKA Flameworking or Torchworking):
Is a method of manipulating small rods and tubes of glass in the flame of a torch to create anything from art glass to scientific glassware. Its origin is vague and disputed, but experts agree that initially the glass was heated over small oil burning ‘lamps", hence the name “Lampworking”.
In the 15th century, “soft glass” was developed by A. Moretti to melt at lower temperatures in order to accommodate this technique. It was used to make small-scale sculptures, and glassware without the overhead expense of traditional glassblowing. Soft glass is still produced by the same Muranese family in Italy. Today, Lamp workers use it to create unique works of art with torches that burn gas and propane, producing a much higher temperature with a larger flame.
Is an Italian term for colored patterns or images made in a glass cane (long rods of glass) that are revealed when cut in cross-sections. The Murrina process first appeared in the Mideast more than 4,000 years ago and was revived by Venetian glassmakers on Murano in the early 16th century. Artists working in glass, design Murrine in a variety of ways from simple circular or square patterns to complex detailed designs to even portraits of people. Layering different colors of molten glass around a core, then heating and stretching it into a rod form Murrine designs. When cool, the rod is sliced into cross-sections of desired thickness with each slice possessing the same pattern in cross-section.
Is an art form that was developed in the 9th century in Central Europe. Originally, sheet glass was cut from large "roundels" (a method of blown glass in which the final form is spun out into a large round plate). Metallic oxides (for coloring) were applied to the surface of the glass and then heated in large kilns. These pieces of "stained" glass were cut and assembled, using strips of lead, into larger compositions, which not only provided light but also became a major architectural design element. They were predominantly used as pictorial themes in cathedrals. Although today, you will find stained glass used in contemporary glass art forms.
Glass can be flattened, beveled, smoothed or carved using techniques like sandblasting, engraving, cutting, grinding, and polishing tools. Abrasive materials hard enough to cut into glass include diamond, silicon carbide, and aluminum oxide. Polishing compounds include pumice, diamond and cerium oxide. Equipment includes belt-sanders, flat lap wheels, sanding discs, files, dremel tools and felt wheels.
Bonding glass together or laminating layers with specialized glues is also part of the Cold Working process.