Art or science?

I got into art to get away from technical fields (physiology, molecular genetics, flow cytometry, and systems administration), but glass fusing can get as technical as anything I’ve done in science or IT.  The complexity comes from the properties of the glass you’re working with, the modifications that you’re trying to produce, and the operating characteristics of the kiln you use.  I’m a rank beginner, with plenty more to learn, but I’ve picked up a bit.  And I learn something new with every firing.

blue bowl

I described the basics of fusing (also called kilnforming) yesterday:  you bake glass in a kiln to change it’s shape (and possibly color) and create new forms.  The kilns used are similar to those used in ceramics and are electric powered (I don’t know of anyone using a gas fired kiln for fusing), though kilns designed specifically for glass are often wide and shallow, and may have elements in the lid as well as the sides.  This makes sense when you consider that most fusing begins with melting assembled pieces on a flat shelf, and even when the final product is a vessel it’s usually shallow.

The kiln I’m using for fusing was passed to me from my grandmother, who used it for firing the china she painted.  It’s a manual Paragon 11inch hex, which I equipped with a digital controller I built (see this post for a bit about that project).


This old kiln is fine for jewelry and small vessels, but the largest I can fire is about 8″ in diameter, so when I saw a used Skutt 1414 (42″ by 25″) on ebay I bought it.  It’s huge, and I can’t wait to use it for larger pieces, but it’s in storage until I can finish building the 3rd room in my studio.

I added a digital controller to my Paragon because glass needs to be heated and cooled in a specific sequence (called a firing schedule) that may consist of a dozen steps.  Programming a digital controller to handle that is the only way to stay sane.  Most firing schedules include the following:

  • moderate (300F/hour) heating from room temperature to 900F to avoid thermal shock
  • rapid heating to about 1100F
  • slow heating to 1250, often with a hold at that temperature to allow air trapped between the glass pieces to escape
  • rapid heating to the “process temperature”, which could be 1350 to tack pieces together, 1430 to soften and round the parts, or 1475 or more to fully fuse the components into a solid mass
  • rapid cooling to the annealing point (900 or 950, depending on the type of glass you use)
  • holding at the annealing point to relieve any strain caused by heating and cooling
  • slow cooling down to about 700F, after which the rate of cooling can increase until the piece is back at room temperature

As you can see, it’s not something that can handled by a kiln that has low, medium and high power settings.  And further complicating matters is that the specific rate (degrees/minute) of cooling or heating and the amount of time spent at each step is dependent on the type of glass you’re using, any added components such as metal foils or wire, and the number of layers of glass you’re fusing together.  And to top it off, it also depends on the design of the kiln, and the placement of pieces inside the kiln, so you can’t just look up a schedule for two layers of 1/8inch glass and expect it to work in your kiln.  Keeping records help a lot, which makes firing projects a lot like the experiments we used to do in the lab.

There’s a lot more to the subject, but what I’ve been up to lately is fairly simple (now that I know what works for my kiln).  I’ve been stacking layers of dichroic glass with colored transparent glass, fully fusing them, and then cutting out simple shapes with my ring saw.  I fire those pieces again at a lower temperature (“fire polish”) to produce smooth and glossy cabochons, that I then make into jewelry, as though they were cabochons of stone.  Here’s two photos of the fired bars, followed by two of the cut cabs before fire polishing.  Thanks for reading!