The medium used in Teresa Kowalski’s artwork is referred to by several names, such as fused glass, kiln formed glass, art glass fusion and warm glass. The reason the term “warm glass” has been widely adopted is because most furnace work, including casting and blowing, takes place between 1700 and 2300 degrees. Compared to that, kiln work has taken the secondary place of being only “warm”, because operations generally included in this category, such as sagging or fusing take place anywhere between 1200 and 1700 degrees Fahrenheit.
During the process of fusing glass, pieces of compatible glass are fired in a kiln to a temperature between 1400 and 1500 degrees F until they are red-hot and melt together. The glass is then fired a second time to a slightly lower temperature to slump into the desired shape and then annealed (a slow cooling process that relieves stress in the glass). Many unexpected and wonderful things can happen in each firing that make each piece unique.
The spectacularly vibrant colors exhibited by dichroic glass are created by a very sophisticated combination of extremely thin, clear, crystalline layers that interact with each other and produce very specific reflected and transmitted colors. There are no absorptive pigments used in this process. This allows all of the light energy to be either reflected or transmitted and, in turn, creates the rich colors that characterize art works created with this glass.
Dichroic glass is created via the application of many individual thin films on the order of one micron in total thickness. These films are composed of alternating high and low index of refraction materials that produce multiple internal reflections. Some of these reflections will add together constructively producing very vibrant reflected colors. Others will add together constructively only in the transmitted direction producing very rich transmitted colors. By varying the thickness of the layers carefully, different colors can be created, all with incredible vibrancy. The fact that the glass exhibits both a transmitted color and a different reflected color is why it is called “dichroic”. Di- is Greek for two, and -chroic is Greek for color, thus combined we have “dichroic”, or two color.