Spectrum 96 is now  available as a tested glass with a COE of 96.  However we shall focus our efforts on Bullseye
glass for this discussion, although much of what we say applies to Spectrum.  You can find Spectrum 96 glass here.
 

FUSING AND SLUMPING GLASS
In recent years glass fusing and slumping have become a major activity in the glass community.  To get started you will need a number of different tools, some of which are listed below.
1. A glass kiln that can reach at least 1600 degrees F.
2. Glass cutters to cut the pieces of glass to be slumped or fused.
3. Running and breaking pliers to break glass.
4. Kiln wash and a wash brush to apply kiln wash to the glass.
5. Safety glasses that protect from the infrared wavelengths emitted from heating glass.
6. High temperature gloves.
7. Glass that is compatible with one another.  (Same COE)
8. Elmers glue to stick the glass together until it is fired.

KEEPING GLASS FROM STICKING
Kiln wash keeps the glass from sticking to the shelves and molds.   It is sometimes called separator.  You can also use fiber paper.  This is a high-temperature ceramic paper that can be placed between the glass and the kiln shelf to prevent sticking.   Fiber paper comes in Thin, 1/32" and 1/8" thicknesses.  The thicker pieces can be used to create Bas Relief work and to make molds, a subject beyond the scope of this presentation.

GLASS
Bullseye, Spectrum and other glasses have all been used successfully in fusing projects.  Bullseye has a COE's of 90.  You can do a compatibility test, to check your glass.

DEVITRIFICATION
  When glass is heated to high temperatures crystal can form on the glass giving it a dull, dirty, matte finish.  This is called devitrification.  In general, this occurs from 1300 deg. F. to 1400 deg. F.  The longer the glass remains at these temperatures, the more crystals grow.  Bullseye cathedral glass stays shiny.  Bullseye opals will devitrify given enough heat and time, but are generally not a problem.  When fusing slowly, a devitrifier, such as Super Spray, should be used.

SETTING UP YOUR KILN
1. Keep it at least a foot and one-half from flammable surfaces and walls.
2. Place it where it is easy to load and unload.
3. Keep it close to your fuse box.
4. Have the proper outlet at hand.  Do not use extension cords as high amperages are needed.
5. Raise it so that heat can escape from the bottom.
6. Make sure it sits level.

GLASS PREPARATION
1. Cut the glass to the desired shape.
2. Grind the edges if needed.
3. Clean the glass thoroughly using soap and water or a commercial glass cleaner..
4. Assemble the glass in the desired form on the kiln shelf.
5. Spray the glass surface with Super Spray by Fuse Master Products.  Note: These sprays will cause an iridescent surface to disappear, a fact that can also lead to artistic creations.
5. Carefully load the kiln with the shelf.

FIRING GLASS
Your kiln will have its own particular properties of firing, but in general, glass goes through four basic stages.

COLD or BRITTLE ZONE
From room temperature to around 900 deg. F., if glass heated or cooled too quickly, it will break.  This is due to thermal shock.

TRANSITIONAL ZONE
From about 900 deg. F. to 1250 deg. F, glass is beginning to change.  The lower end of this temperature is referred to as the strain point, the upper end the softening point with the annealing point somewhere in between.  Annealing simply means you heat glass (and cool it) slowly to relieve the internal stresses built up by the heat.

WORKABLE or PLIABLE ZONE
From about 1250 deg. F. to 1350 deg. F., glass will begin to take the shape that gravity allows it.  This is the zone where glass is slumped.  A piece of glass held up by four pegs at each corner will begin to "slump" down toward the kiln floor.

MOLTEN or FLUID ZONE
Above 1350 deg. F. glass become a fluid like honey and can flow.  Fusing occurs around 1500 - 1600 degrees..

THE LOG
It is important that you keep a log of each firing.  This will help you make changes and find possible errors later.
 

HEATING RATES   The two primary concerns on heating are 1) avoiding thermal shock and 2) preventing devitrification. Thermal shock - breakage due to excessive heat differential within the glass body - can be prevented by a slow rate of heating below the strain point. Devitrification - a crystalline scum on the glass surface - is rarely a problem with Bullseye glasses manufactured in recent years. Using an overglaze or rapidly heating the glass through that temperature range where devitrification may occur (1300 ° - 1400 ° F) will prevent it. The following chart is a rough schedule for heating Bullseye glasses. It assumes a first time firing in which none of the individual pieces of glass in the lay-up is greater than 25% of the total glass mass. It further assumes a kiln with top-firing elements. For a top-fired slumping of a pre-fused piece, double the initial heating times. For a side-fired slumping of a pre-fused piece, increase the initial heating by at least 2.5 times. HEATING A TYPICAL (12" DIAMETER) COMPOSITION OF BULLSEYE GLASS Thickness(inches) Initial Heating (Room temp. to 1000°F) rate(°F/HR) Rapid Heating Rate(A) For Full  Fuse(From 1000° To 1500° F & above) (B)(°F/HR) Soak Time At Full Fuse (1500°F) Cooling Rate* From Full Fuse (or Slump) To 960° (°F/HR) 1/8" 600 (C) (C) AFAP** 3/16" 525 (C) (C) AFAP** 1/4" 450 1000 ° F 10 mins AFAP** 3/8" 375 1000 ° F 10 mins AFAP** ** AFAP = As fast as possible *Most kilns will not cool this rapidly due to residual heat in the refractories. Allowing the kiln to cool at its own rate between 750 ° F and room temperature is usually adequate for the final cooling stage. This may result in an actual cooling rate slower than that shown above. Cooling the work by opening the kiln door or large vent hole, however, risks thermal shock.     (A) If you are having problems with bubbles, try slowing the rate of heating up to full fuse. Inserting a half-hour soak at 1250 ° F may also help "squeeze" air from between the glass pieces before the edges seal and trap bubbles.    (B) A "full fuse" - generally considered to have occurred when the surface of the glass is completely smooth and free of bumps - is dependent on both temperature and time. Some kilns will achieve a full fuse of Bullseye at 1450 ° F with a 45 minute soak. The same kiln may achieve full fuse with a much shorter (5 minutes or less) soak when taken to 1540 ° F. At the factory we typically program a full fuse at 1500 ° F with a 10 minute soak.    (C) Glass lay-ups of this size (12" diameter) which are less than 1/4" thick should not be taken to a full fusing temperature. They will distort in shape and are extremely prone to bubbles. They may, however, be successfully slumped to a shallow depth or tack fused at ~1375 ° F. See Note (A, SLUMP FIRINGS) above.

THIS SCHEDULE IS COURTESY OF THE BULLSEYE GLASS COMPANY

 

ANNEALING SCHEDULE   Annealing, the controlled cooling of a glass, is critical to its longevity. Glasses which are not properly annealed will contain stress which may result in breakage before or at any time subsequent to their removal from the kiln. The following chart represents a simple schedule used routinely in Bullseye's factory studio. Annealing schedules for thicker pieces (up to 8") are available from the factory upon request.     ANNEALING A TYPICAL (12" DIAMETER) BULLSEYE GLASS PROJECT Thickness (inches) Anneal Soak @ 960 ° F (In Minutes) Anneal Cooling Rate 960-750° F (°F/HR) Actual Time In Range 960-750 ° F Cooling Rate* 750 ° F To Room Temp (°F/HR) Actual Time* In Range (750°F To Room Temp) 1/8" 15 min 420 30 min 1013 40 min 3/16" 23 min 280 45 min 675 60 min 1/4" 30 min 210 60 min 500 80 min 3/8" 45 min 140 90 min 335 120 min *Most kilns will not cool this rapidly due to residual heat in the refractories. Allowing the kiln to cool at its own rate between 750 ° F and room temperature is usually adequate for the final cooling stage. This may result in an actual cooling rate slower than that shown above. Cooling the work by opening the kiln door or large vent hole, however, risks thermal shock. THIS SCHEDULE IS COURTESY OF THE BULLSEYE GLASS COMPANY

SLUMPING
Glass can be slumped into, over and through a mold at temperatures between 1200 deg. F. and 1350 deg. F.  Molds can be made of clay (green ware), metals (not aluminum or copper), castable cements, Luminar papers and insulating cements.  The manufacturers can provide data on their products.   Here are some of the characteristics to consider when choosing a mold.

Metal Molds usually contract and expand faster then glass and are usually slumped over, rather than in.  If the glass slumps into the metal, the faster contraction can crack the glass.  Metal molds are durable and will last a long time.  They can also provide a very shiny surface against the glass.  Common metals are stainless steel, cold rolled steel, cast iron , brass and nichrome wires.

Clay Molds have less contraction and are often slumped in.  The glass next to the clay will take on the texture of the clay, so be sure the good side of your project is not against the clay.

Castable Cements are dry powders that you add water to and then make your own mold.  They are usually mixed to the consistency of cement and then trowelled over the form you wish to make a mold of.  To keep castable cement from sticking to the model, spray the model with PAM or wipe it with suntan lotion.  DO NOT USE PETROLEUM BASED PRODUCTS.
 
 
 

COMPATIBILITY TESTING
You can test glass for compatibility using the Reynolds Interface Compatibility Test (R.I.C.T.)
This test uses pieces of clear glass as a base.  Perform the test as follows:

1. Cut a piece of your main glass 1" by 8"  This is your base glass on which the other glass will be placed.
2. Cut samples of various colored glass to be tested for compatibility 1" by 1/2".
3. Cut 1" squares of your main glass, so that you have one more piece than testing pieces..
    i.e.: if you are testing 4 colored pieces, you will need 5 - 1" main glass pieces.
4. Lay the long main  glass down.
5. Starting at the left side, place a main glass square, then colored glass sample, main square, colored glass sample . . . . and finally a main square on the right hand end.
6. Heat the bar of glass to a full fuse and anneal.
7. Place the cooled glass between two backlit polarized lenses.
8. Rotate the lenses to the darkest orientation.
9. Move the bar 45 deg.  Samples that have a COE different from the base glass will show a white glow along the edge of the sample.  The size and brightness of the glow indicates the amount of mismatch between the glass.