I get asked many questions about this. Not being an experienced potter I thought i would learn as much as I could so I could refer customer to a credible source. Here is a great article from Ceramics Network. If you want to read the whole article click on the link.
To learn more about mica powder specifically I have cut and pasted the article below.
by Kate and Will Jacobson
For the past year, we’ve been exploring the sub- tle luster and compelling color palette of mica as a glaze element. We usually teach naked raku, but wanted to give our students some other low- fire techniques to explore. While preparing for a workshop, we tested the reaction of various terra sigillatas, colored porcelain slips, and even acrylic paint in the ferric chloride saggar process.
Why did we try a copper-colored acrylic paint? We discovered the pigment in the copper color is mica coated with titanium and iron. We thought it would be a good source for these oxides. Turns out, it was a good source of mica.
Mica, a mineral often used in cosmetics for it shimmery essence and in electronics for its insulat- ing properties, is a very refractory mineral. It easily withstands the 1472°F (800°C), (cone 015), temper- ature a lot of bare-clay firing techniques call for, mak- ing it ideal for using in several low-fire techniques such as naked raku, ferric chloride saggar, horsehair firing, clay saggar and pit-fired ceramics. Detailed explanations of these firing techniques are well cov- ered in the book Naked Raku and Related Bare Clay Techniques published by The American Ceramic Society (www.CeramicArtsDaily.org/bookstore).
Glazing with Mica
There are several ways to use mica as a glaze el- ement in low-fire techniques. Wearing a dusk mask, mix 5 grams of mica powder into one cup of terra sigillata made from OM4 ball clay.
Life Aquatic, sponged and painted with copper colored “mica paint” and block printed on the surface, ferric- chloride red.
This will give you a starting point for your color. The more mica you add, the more saturated the color becomes.
Next, brush two coats of plain terra sigillata on a bone dry piece. Then apply a topcoat of the mica sigillata. This can be brushed, sponged, painted, stamped, sprayed, etc. (figures 1 and 2).
1. Applying mica paint (matte acrylic medium mixed with 1⁄2 gram of colored mica powder) with a stamp.
3. Wave, OM4 sigillata, copper-colored mica paint sponged on surface, ferric chloride red.
When dry, burnish with a piece of plastic wrap and bisque fire to 1382°F, (cone 017). Your piece is now ready to be used in one of many low-fire techniques. The mica gives an added luster and subtle sheen that emanates from within the clay. This application also works well with any bare clay technique that fire at or under 1472°F.
Making Mica Paint
Another way to use mica is to mix your own mica paint. This is particularly effective in ferric chlo- ride, aluminum-foil saggar firings. Mix two table- spoons of matte acrylic medium (available at art supply stores) with 1⁄2 gram of colored mica pow-
2. Brushing a top coat of Jacobson’s Super Copper mica sigillata on top of 2 coats of regular OM4 sigillata.
4. Applying colored mica dry rub onto a slightly dry, textured clay surface with a soft bristle make-up brush.
der. Paint or sponge this mixture onto an already bisque-fired pot that has been coated with either regular OM4 terra sigillata or mica sigillata.
Once dry, and wearing latex gloves and a respi- rator, paint or pour ferric chloride on the piece. Then, wrap the piece with two layers of alumi- num foil, making sure you get a tight seal. Fire the piece rapidly to 1472°F, then back off the temperature to 1382°F and hold for 10 minutes. Warning: Wear an appropriate respirator when firing with ferric chloride as you must take ex- treme caution to not inhale the fumes.
After firing and unwrapping the piece, take a soft brush and remove some of the residual dust.
5. Pineapple, 10 inches (25 cm) in height, Laguna Amador Clay, mica dry rub, heated and smoked.
In order to fix the surface, use a UV-resistant fixa- tive spray to seal and protect (figure 3).
We have discovered that one of the properties of mica is that it does not trap carbon. This is good news because it allows for contrast between the clay and mica in a smoke firing. This technique works well with highly textured forms. We like to call this the ‘dry rub’ technique. Use a soft bristle make-up brush to scrub dry mica powder onto a not-quite- leather-hard pot (figure 4). The mica is pushed into the clay and then the excess is brushed off. Bisque fire the piece to cone 017. Now it’s ready to fire in a raku kiln followed by reduction in a smoke cham- ber. The result is shimmering mica embedded into the clay juxtaposed against the matte black of the carbon-infused clay (figure 5).