For a set of earrings, ring and necklace. Further exploring this idea. Now the previous piece seems so primitive :p
The candidate stones are grey moonstones and blue lace agates (not dyed). And black glass.
Transparent grey enamels over opal enamel over copper.
Alternating layers of grey opal, white opal and black vitrifiable pigment (on glaze paints).
It is difficult to show the layered effect on a picture.