Factors to consider when selecting a firing schedule

First, envision what you want your finished piece to look like and ask yourself the following questions:

  • What is the size (diameter) of the piece? How many layers thick will it be?
  • What is the desired finished look?
  • Will it be a full fuse, a more textural tack fuse, a combination of both?
  • Will it be slumped or draped to become a more 3 dimensional and possibly functional piece?
  • Will it be embellished with any surface decorations like enamels or metallic paints?

The size of your project is defined by both the diameter of the piece as well as the number of layers of glass. Glass as a material is a very poor heat conductor. The larger or thicker your project is, the more slowly it needs be fired so that the glass has more time to heat or cool evenly all of the way through. Imagine that you are going to bake a cake. You have set your oven on preheat to heat it up quickly, put the cake into the oven to bake, and forgot to change the dial setting to bake. When the timer goes off, you look in the oven and discover that the cake is overcooked and possibly burned on the edges, yet the center is still sunken and uncooked.
It’s just the same for glass. If you heat the glass too quickly, the edges may be fused to the desired finish you like, but the center hasn’t finished fusing. One solution would be to soak the piece at the process temperature for a longer period of time, but you are also taking the risk that devitrification (visible clouding due to crystallization) on the surface or that the edges will over fire and have an unusual appearance.Another possible scenario is that the edges of the glass have melted more quickly, trapping a large amount of air in the center of the piece which expands into large bubbles within the glass, thus distorting the design. Both scenarios could have been avoided simply by slowing down the firing program.Think about your finished piece again. You are creating a 10” bowl that will have a full fused appearance with some added textural design elements that will be added using liquid stringer. The finished appearance will also have Hanovia gold added as accents and be slumped into a 10” bowl mold.

Seldom can a fused piece be finished in one firing. It’s usually necessary to fire your piece multiple times in order to achieve the finished look that you have envisioned. With this in mind, make a list of the steps that you will need to do to create this piece, then organize them in order by process temperature from the hottest to the coolest.

By order of process, the full fuse is the hottest process and will be the first firing, followed by 3 different firings to create your original glass art piece.

This Ramp-Hold Firing Profile from Paragon might also come in handy!