Yesterday I told you that Wendy Talaro has graciously shared her tutorial on fusing glass. I’m so glad, because even though I’ve tried it a few times, I feel in no way qualified to speak at length on the how tos! It’s a lovely thing when folks are so willing to share their expertise
Glass Fusing Primer
So What Is Glass Fusing?
Glass fusing is the process of assembling pieces of fusing compatible glass (i.e. glass that has the same rate of expansion/contraction when heated or cooled) and melting those pieces in an electric kiln until they stick together, becoming one single piece out of many. The look of finished pieces could be described as stained glass without the leading.
Don’t let the equipment intimidate you. Just think of a glass fusing kiln as a very expensive oversized electric oven on steroids. That said, let’s move on now to describe the qualities of the glass that you will be using to create your art and to define compatibility.
Glass Types and Manufacturers
Technically any piece of glass is compatible with itself. For instance, you could smash a Coke bottle and fuse all of the pieces into a new form or take an ordinary pane of window glass, cut it up and fuse it together again. Glass is a curious material. Neither crystalline nor liquid, it is a solid at room temperature. By adding heat generated by a kiln, glass can be made to visibly flow. There are three principles to remember when glass liquifies and becomes viscous: temperature, gravity and surface tension. The hotter the glass is, the less viscous it becomes and the more it visibly obeys gravity and the less surface tension constricts its flow.
Solids expand when heated. (A notable exception is water, which actually expands when it is cooled to the temperature until it forms the solid we know as ice.) Glass also expands but different formulations of glass have different rates of expansion depending upon the manufacturer, batch, color and chemical composition. Glass is composed primarily of silica (the primary component of sand), soda ash, and lime. The quality of glass can be improved by adding lead and potash, the coefficient of expansion lowered by adding boron, and colors are created by the addition of sulfur, cobalt, gold, and other metals.
The term “coefficient of expansion” describes the change in length of heated glass as a function of change in temperature measured in degrees Centigrade. Glasses that share the same rate of expansion are said to have the same coefficient of expansion or COE. The three primary manufacturers of Tested Compatible (i.e. factory tested in labs to verify the coefficient of expansion) fusible art glass are Bullseye, which is based in Seattle, Washington; Uroboros Glass Studios, which is in Portland, Oregon; and Spectrum Glass Company in Woodinville, Washington. Below is a chart that lists several manufacturers of glass and the measured ranges of COE.
Uroboros 90 and 96 COE
Bottle Glass 89-92
Pyrex or Borosilicate Glass 32
Float Plate 85-87
Float plate or what is more commonly referred to as window glass has a COE range from 85 to 87. This type of glass receives its name from the manufacturing process. The molten glass is fed to a float bath of more than 120 tons of molten tin and the glass thickness is determined by the rate at which the glass is floated onto the tin, thus producing glass with the characteristic doublesided smoothness associated with modern production methods.
For project success, it is necessary to use glass that has the same COE in the same piece. Mixing glass of different coefficients of expansion results in stress fractures that form as the fused pieces cool. Effetre and Murano are commonly used in lampworking, which is working molten glass in an open flame produced by a torch. Bullseye, Uroboros, and Spectrum are used in fusing and lampworking. Borosilicate glass is frequently used in scientific labware and for elaborate sculptural figurine lampworking with fine details. The low coefficient of expansion of borosilicate glass allows for sculptural flourishes that would be impossible with other glasses.
Bullseye and Uroboros manufacture glass for fusing in primarily two thicknesses, 1/16” and 1/8”. The thinner of the two is favored for jewelry and other small items because of the ability to layer the glass for different color effects and visual textures without adding a lot of bulk or mass to a finished design. It may help conceptually to think of designing in fused glass as a sandwich. Design with consideration for the thickness for the finished piece. Four layers of 1/16” thick glass results in a piece that is 1/4” of an inch thick.
The thicker the piece, the longer it has to anneal in a kiln. Annealing is the process of creating temperature uniformity throughout a fused piece and then cooling it slowly so that stress fractures do not form. Stress fractures can be very sneaky. A piece that has been well-annealed is structurally stable at the molecular level, whereas a piece that has internal stresses may not manifest those stresses immediately, nor will that stress be visible to the naked eye. A piece can look fine day after day only to inevitably crack of its own accord eventually due to the buildup of internal stress that was present from the day the piece emerged from the kiln. Other pieces manifest stress fractures due to glass incompatibility immediately.
Tools and Equipment
Glass fusing is not inexpensive. As a hobby, the materials are costly, particularly when you start to include dichroic glass in your pieces. This is to say nothing about the cost of the kiln itself, kiln furniture, and shelves and adjunct optional tools such as a diamond blade saw or a grinder with multiple grades (coarse, medium, fine, and extra fine) of grinding bits. At a minimum, you will need to invest in the following equipment:
Oil reservoir glass cutter – pencil or pistol grip configuration
6” or 8” running pliers
Breaking / grozing pliers
Non-skid cork backed steel ruler 12”
Cutting mat 8.5” x 12”
10 or 12 square per inch plastic canvas
Gloves that allow manual dexterity and feeling but still allow you to protect
Drafting table brush or dusting brush
The type of glass cutter chosen will be a matter of personal preference and comfort, as will be the choice in running plier size. Eight inch running pliers will provide more leverage for running scores in thicker and larger pieces of glass. Grozing pliers are good for removing small pieces that do not break off readily along the score line. The cork-backed steel ruler allows you to cut straight lines, using the ruler as the cutting guide while you run a glass cutter along the ruler’s length. The cutting mat provides a firm, non-scratching surface for cutting glass pieces and plastic canvas allows the fine splinters of glass to fall through the grid. The drafting table brush or dusting brush is for cleaning off your surfaces of glass small debris. Whatever you do, do not use the side of your hand or your fingers to sweep debris off the cutting surface! You’ll be picking glass splinters out of the side of your hand for hours.
Other supplies that will be desirable to have are as follows:
1) Sharpie or Staedler permanent marking pen (extra fine point)
2) Toothpicks for applying white or cyanoacrylate glue
3) White craft glue for securing cleaned glass during assembly before firing: Elmer’s, Sobo,
Aleene’s. Cyanoacrylate glue is less likely to leave residue after firing, although the fumes
produced during burnout are considerably more toxic than white glue. All glue is to be used
sparingly, just enough to secure the pieces in place as they are assembled and then
transported to the kiln for firing.
4) Fine tweezers for manipulating small pieces of glass
5) Morton grid system for production or precision cutting of glass.
6) 90% or greater isopropyl alcohol or commercial grade acetone (please don’t use fingernail
polish remover) for cleaning glass of cutting oil, marker ink, and fingerprints before final
assembly and firing
7) Plastic bags with zipper enclosures for carrying scrap glass or work in progress. Freezer bags
are highly recommended due to their thickness.
8) Pad of paper or notebook for sketching and/or recording ideas and design strategies, graphite
pencil or colored pencils, eraser
9) Band-aids and tea tree oil (cuts are almost inevitable)
10) High quality respirator mask with changeable filters (to be used when scraping and sanding
spent kiln wash off kiln shelves). This applies if you have your own kiln and shelves. Do not
skimp on safety equipment.
copyright 2009 Wendy Talaro
Image: Wendy Talaro