You know that old chestnut about necessity being the mother of invention? Nowhere is it more true than in a kiln-glass studio. At least in mine. I’ve repeatedly found myself having to research subjects about which I was completely ignorant, learning a new skill (such as brazing stainless steel for a sculpture base), or experimenting with an unusual new material.
Case in point: I’ve been working with glass frit powder in a variation of the pate de verre technique, making three-dimensional glass bird feathers. Many real feathers have iridescent surfaces and glint with metallic tints when the light catches them at certain angles. I wanted to figure out a way to emulate this effect, but Bullseye Glass doesn’t manufacture iridescent frit. What to do?
Through a bit of research online I learned that some glass artists have experimented with mica powder in their designs, with mixed results. The tinted mica used for homemade cosmetics (manufactured by Jacquard Products) can be purchased on Amazon, and comes in beautiful shades. In its natural state, mica is a sparkly, transparent silicate mineral that cleaves in flakes, also called “books”. It remains elastic at high temperatures, and was once used for furnace viewing ports. Today mica is can be found in everything from electronics to toothpaste to eyeshadow.
Processed mica has some characteristics that make it tricky to work with. Some shades are more stable than others at high temperatures, for instance. This means some trial and error is required to determine how color-safe the powder is at your peak firing temperature.
I wanted to create an iridescent surface at tack-fuse temperatures (1225-1275 degrees F), but for my own curiosity, I also did some color testing in the full-fuse range (1490 degrees F). The results were very interesting, and I recorded some of the effects from various firings with photos.
Here’s a critical factoid: mica powder will stick to glass when fired, but it will not stick to itself. This means that mica powder can be applied to glass in a very thin layer, but not built up thickly—only the particles in direct contact with the glass surface will adhere.
I took a 4″ x 7″ sheet of clear Tekta and tack-fused a layer of black opal powder to it. I then rubbed mica powders of various colors into the rough surface, and also tried mixing some mica with different shades of frit powder in a 3:1 blend—which I sifted onto the surface in bands. I then tack-fused it at 1275. The places where I had sifted the frit/mica mixture thickly didn’t adhere, and flaked off after firing (except for the thin layer directly against the base glass). I surmised this was because there was too much mica relative to frit, which interfered with adherence.
To make things even more interesting, I then laid a strip of clear 3 mm Tekta across the top and refired the whole shebang at 1490 degrees F.
Predictably, the results were mixed. The spots on the bottom third of the panel where I rubbed pure mica into the surface resulted in truly beautiful, subtle metallic finishes in lovely shades of blue, purple, and ruby. Other colors/applications were less successful: gray, green, and bright yellow tended to burn out to a whitish grey. Capping the mica/frit powder with a layer of clear powder resulted in almost an orange peel texture (see the upper left side, second swatch from the top). Blue held up very well, as did all colors in the copper range. Ruby and purple were also quite color-stable at full-fuse temperature. The mica made an interesting streaky texture where it was subsumed below the overlaid Tekta strip.
I took the samples to Bullseye’s Santa Fe Resource Center, where staff member Meredith Gill had asked me to show her the results of my mica tests. She used sheets of polarizing film and examined the full-fused panel on a light table, looking for signs of stress in the glass (caused by incompatibility that might have been created by adding a foreign material like mica to the glass). Fortunately, she didn’t see any indication of this, so the mica didn’t appear to impact the stability of the glass.
Of course, I’ve only scratched the surface of what effects could be created using mica combined with frit powders. For instance, I didn’t test mica with coarser grades of frit. However, my limited testing did point me in the direction I needed to go with my own work, and the two small frit feathers pictured below show the effect gained by rubbing a bit of colored mica over them and then firing to 1250 degrees F.
Some of the mica washed off after firing, but enough stuck to the surface to give the feathers a subtle but noticeable warm shimmer. My next challenge will be to tackle a peacock plume…that will be the real acid test for mica’s magic.
Editor’s note: Guest blogger Lois Manno is a New Mexico-based writer, artist, and illustrator. She’s also a newcomer to kiln-glass who’s agreed to share her adventures in her new medium here. She blogs at www.glassbirdstudios.com.