I've worked out my technique for crafting eyeballs for Halfland puppets. I bought some air dry clay at an office supply store, of all places, something I never would have bought ordinarily. It turned out to have very interesting properties for this task that make it ideal. It shapes smoothly, dries on its own without special equipment, carves nicely in the greenware stage before it's dry, and burnishes with a soft cloth to a wonderful, gentle sheen, seen above. Reminds me a bit of an eggshell finish. I love its natural dry color as well. No need to paint the whites.
Koi of Enlightenment's eyes and other paintings years back, I remembered that real gold leaf, not metallic paint, not iridescent mica, only real gold leaf, sitting at the bottom of a stack of painted layers carries forward with magical effect. It's as though the gold imbues whatever colors placed on top of it with an inner light, like magnified jewels. I applied gold size to flat faces of the balls and proceeded to layer up watercolors and other mediums to see what a mermaid's irises might be.
Back in New York, I bought several expensive pairs of hand-blown glass eyes from a taxidermy shop in Manhattan. Two seen top left, I noticed that what really gave them depth was how the pupils were not on the surface of the cornea but rather embedded under a thick clear layer of glass. I copied this with my liquid diamond glaze medium, building up the layers as each step dried. I used paper punches in black paper for pupils to get them as perfectly round as possible. My favorite results seen lower right. A smaller version, without its pupil, seen lower left, in the test Kyra puppet's face.
On the top right are two whimsical glass eyes bought on that same trip that I embedded into clay and painted many years ago. These were made for a soft plush monster toy idea I had so I made them have crazed bloodshot look by painting the whites with a porcelain crackle medium and tinting the craze with stark red glaze.