Picture 017

More spirals.

But look, no huge contrasting colour dot, and you can see the native colours all the way to the center. How was that done?

With a very skinny mandrel; use it just like a metal pontil. Push into the soft glass, spin gently to form a spiral, then heat the mandrel red hot (but not the marble) and let it slip back out, taking only a small glob of glass with it.

The marble itself was another hell-child. It had equatorial lumps that would not even out; the white, gray and orange glass seemed to be barely on speaking terms with each other, let alone willing to lay down into smooth stripes; and the gray started reducing and blistering at the edges. It was a real nuisance.

It's going back in the kiln sometime soon for another try.