How I would attempt to do this.
This is just a hunch. But I would use my favorite cone 10 porcellin clay - Highwater's Helios
and make a vessel. Trim until translusent. Get a dremel tool with a round diamond tip and make
a design on inside. Borrow the light box from the art dept and flip the bowl upside down on
light box. Then lightly match the inside etching with an exterior etching, being careful
NOT to make it pierce work. Then glaze the bisqued piece with clear glaze.
I'd fire this cone 10 reduction, since clear fired in reduction becomes grey, which would
make it appear clear on the translucent white clay body.
If it matched Pinnell's example, great! If not, re-group and try something else.
But this would be my starting point if I were to try figuring out this technique.
PS - Pete is a really neat potter to sit down and talk with if you ever get a chance.
In my most humble opinion,