Fused glass
Encyclopedia
Fused glass is a term used to describe glass
that has been fired (heat-processed) in a kiln
at a range of high temperatures from 593 °C (1,099.4 °F) to 816 °C (1,500.8 °F). There are 3 main distinctions for temperature application and the resulting effect on the glass.
Firing in the lower ranges of these temperatures 593–677 °C (1,099.4–1,250.6 F) is called slumping
.
Firing in the middle ranges of these temperatures 677–732 °C (1,250.6–1,349.6 F) is considered "tack fusing".
Firing the glass at the higher spectrum of this range 732–816 °C (1,349.6–1,500.8 F) is a "full fuse".
All of these techniques can be applied to one glass work in separate firings to add depth, relief and shape.
. Glassblowing
largely supplanted fusing due to its greater efficiency and utility.
While glass working in general enjoyed a revival during the Renaissance, fusing was largely ignored during this period as well. Fusing began to regain popularity in the early part of the 20th century, particularly in the U.S. during the 1960s. Modern glass fusing is a widespread hobby but the technique is also gaining popularity in the world of fine art.
. It is then allowed to cool slowly over a specified time, soaking at specified temperature ranges which are essential to the annealing
process. This prevents uneven cooling and breakage and produces a strong finished product.
This cooling takes place normally for a period of 10–12 hours in 3 stages.
The first stage- the rapid cool period is meant to place the glass into the upper end of the annealing range 516 °C (960.8 °F). The second stage- the anneal soak at 516 °C (960.8 °F) is meant to equalize the temperature at the core and the surface of the glass at 516 °C (960.8 °F) relieving the stress between those areas. The last stage, once all areas have had time to reach a consistent temperature, is the final journey to room temperature. The kiln is slowly brought down over the course of 2 hours to 371 °C (699.8 °F), soaked for 2 hours at 371 °C (699.8 °F), down again to 260 °C (500 °F) which ends the firing schedule. The glass will remain in the unopened kiln until the pyrometer
reads room temperature.
Note that these temperatures are not hard and fast rules. Depending on the kiln, the size of the project, the number of layers, the desired finished look, and even the brand of glass, ramp and soak temperatures and times may vary.
, glass tiles
, and jewellery, notably beads. Slumping techniques allow the creation of larger, functional pieces like dishes, bowls, plates, and ashtrays. Producing functional pieces generally requires 2 or more separate firings, one to fuse the glass and a second to shape it.
Since the 1970s, more hobbyists have focused on using kiln-fused glass to make beads and components for jewellery
. This has become especially popular since the introduction of glass manufactured for the specific purpose of fusing in a kiln.
Glass
Glass is an amorphous solid material. Glasses are typically brittle and optically transparent.The most familiar type of glass, used for centuries in windows and drinking vessels, is soda-lime glass, composed of about 75% silica plus Na2O, CaO, and several minor additives...
that has been fired (heat-processed) in a kiln
Kiln
A kiln is a thermally insulated chamber, or oven, in which a controlled temperature regime is produced. Uses include the hardening, burning or drying of materials...
at a range of high temperatures from 593 °C (1,099.4 °F) to 816 °C (1,500.8 °F). There are 3 main distinctions for temperature application and the resulting effect on the glass.
Firing in the lower ranges of these temperatures 593–677 °C (1,099.4–1,250.6 F) is called slumping
Slumping
Slumping is one broad technique of warm glass working, for the forming of glass by applying heat to the point where the glass will soften. The increasing fluidity of the glass with temperature causes the glass to 'slump' into or onto the mold under the force of gravity.- Technique :Glass is most...
.
Firing in the middle ranges of these temperatures 677–732 °C (1,250.6–1,349.6 F) is considered "tack fusing".
Firing the glass at the higher spectrum of this range 732–816 °C (1,349.6–1,500.8 F) is a "full fuse".
All of these techniques can be applied to one glass work in separate firings to add depth, relief and shape.
History
While the precise origins of glass fusing techniques are not known with certainty, there is archeological evidence that the Egyptians were familiar with rudimentary techniques ca. 2000 BCE.Gil Reynolds: The Fused Glass Handbook. Hidden Valley Books; Scottsdale, Arizona 1987, ISBN 0-915807-02-5 Although this date is generally accepted by all researchers, some historians argue that the earliest fusing techniques were first developed by the Romans, who were much more prolific glassworkers.Boyce Lundstrom: Kiln Firing Glass. Vitreous Publications; Colton, Oregon 1983, ISBN 0-9612282-3-7 Fusing was the primary method of making small glass objects for approximately 2,000 years, until the development of the glass blowpipeBlowpipe
Blowpipe can refer to:*The Blowpipe missile*Blowgun, a weapon*Blowpipe *Blowpipe , several Transformers characters....
. Glassblowing
Glassblowing
Glassblowing is a glassforming technique that involves inflating molten glass into a bubble, or parison, with the aid of a blowpipe, or blow tube...
largely supplanted fusing due to its greater efficiency and utility.
While glass working in general enjoyed a revival during the Renaissance, fusing was largely ignored during this period as well. Fusing began to regain popularity in the early part of the 20th century, particularly in the U.S. during the 1960s. Modern glass fusing is a widespread hobby but the technique is also gaining popularity in the world of fine art.
Techniques
Most contemporary fusing methods involve stacking, or layering thin sheets of glass, often using different colors to create patterns or simple images. The stack is then placed inside the kiln (which is almost always electric, but can be heated by gas or wood) and then heated through a series of ramps (rapid heating cycles) and soaks (holding the temperature at a specific point) until the separate pieces begin to bond together. The longer the kiln is held at the maximum temperature the more thoroughly the stack will fuse, eventually softening and rounding the edges of the original shape. Once the desired effect has been achieved at the maximum desired temperature, the kiln temperature will be brought down quickly through the temperature range of 815 °C (1,499 °F) to 573 °C (1,063.4 °F) in order to avoid devitrificationDevitrification
Devitrification is the opposite of vitrification, i.e., the process of crystallization in a formerly crystal-free glass. The term is derived from the Latin vitreus, meaning glassy and transparent.-Devitrification in glass art:...
. It is then allowed to cool slowly over a specified time, soaking at specified temperature ranges which are essential to the annealing
Annealing (glass)
Annealing is a process of slowly cooling glass to relieve internal stresses after it was formed. The process may be carried out in a temperature-controlled kiln known as a Lehr. Glass which has not been annealed is liable to crack or shatter when subjected to a relatively small temperature change...
process. This prevents uneven cooling and breakage and produces a strong finished product.
This cooling takes place normally for a period of 10–12 hours in 3 stages.
The first stage- the rapid cool period is meant to place the glass into the upper end of the annealing range 516 °C (960.8 °F). The second stage- the anneal soak at 516 °C (960.8 °F) is meant to equalize the temperature at the core and the surface of the glass at 516 °C (960.8 °F) relieving the stress between those areas. The last stage, once all areas have had time to reach a consistent temperature, is the final journey to room temperature. The kiln is slowly brought down over the course of 2 hours to 371 °C (699.8 °F), soaked for 2 hours at 371 °C (699.8 °F), down again to 260 °C (500 °F) which ends the firing schedule. The glass will remain in the unopened kiln until the pyrometer
Pyrometer
A pyrometer is a non-contacting device that intercepts and measures thermal radiation, a process known as pyrometry.This device can be used to determine the temperature of an object's surface....
reads room temperature.
Note that these temperatures are not hard and fast rules. Depending on the kiln, the size of the project, the number of layers, the desired finished look, and even the brand of glass, ramp and soak temperatures and times may vary.
Finished products
Fused glass techniques are generally used to create Art glassArt glass
Definitions of art glass can be as complex and contentious as definitions of what constitutes "art" and will inevitably include many refinements and exceptions...
, glass tiles
Glass tiles
Glass tiles are pieces of glass formed into consistent shapes. Glass was used in mosaics as early as 2500 BC, but it took until the 3rd Century BC before innovative artisans in Greece, Persia and India created glass tiles....
, and jewellery, notably beads. Slumping techniques allow the creation of larger, functional pieces like dishes, bowls, plates, and ashtrays. Producing functional pieces generally requires 2 or more separate firings, one to fuse the glass and a second to shape it.
Since the 1970s, more hobbyists have focused on using kiln-fused glass to make beads and components for jewellery
Jewellery
Jewellery or jewelry is a form of personal adornment, such as brooches, rings, necklaces, earrings, and bracelets.With some exceptions, such as medical alert bracelets or military dog tags, jewellery normally differs from other items of personal adornment in that it has no other purpose than to...
. This has become especially popular since the introduction of glass manufactured for the specific purpose of fusing in a kiln.