The first step is to create the “pattern bar”. This is done by creating a pattern bar loaf which is then cut into quarter inch slices (the “pattern bars”) using a diamond blade wet saw. The pattern bar loaf is made by cutting strips of glass in various colors of interest and melting (fusing) them together to create the solid glass loaf. Typically, the loaf is 9 inches by 4 inches and 1.5 to 2 inches thick. The glass strips are brought to 1500 degrees to totally melt them together. In order to maintain the desired thickness, the glass forming the loaf must be contained on the shelf. If it were not contained, it would spread out to its natural thickness of a quarter of an inch. Figures 1 and 2 show several pattern bar loaves before and after fusing. This process typically takes 36 hours from start of the firing to removal of the loaves from the kiln.
The pattern bar loaves are then cut using a diamond blade wet saw into quarter inch pattern bars. These slices are called “pattern bars” because two slices could be book-ended to form a pattern. See Figures 3 and 4 for an example. The pattern bars can then be used as the building block to create a design. The pattern bars that result from the cutting tend to have rough edges which result in fusing issues. To deal with this, the cut bars are put in a rock tumbler for 16 to 24 hours to smooth out the edges. After that, the bars are arranged (typically on a base piece of glass) to create the design. See Figure 5 for an example of a pattern bar piece assembled and ready for fuse firing.
The fusion process is essentially the same as for Mosaics. (See the Mosaic write-up.) The key differences are that the temperature is brought up more slowly (175 degrees per hour) and the annealing at 900 degrees is held longer (2 to 3 hours). Also as with Mosaic pieces that need slumping, pattern bar pieces are placed on a mold. Again, the temperature is brought up more slowly (175 degrees per hour) than for Mosaics. Figure 6 shows the resultant “Pattern Bar” piece.