You could use some clay mixed with pearl ex powders to more closely mimic Opal perhaps.
Making a cane
ХОЛОДНЫЙ ФАРФОР , ПЛАСТИКА (МАСТЕР КЛАССЫ)
Холодный фарфор мастер класс букет сирени.
Polymer Clay Zebra Millefiori Cane Tutorial
Polymer Clay Millefiori Cane: Photo Zebra Cane Tutorial by KatersAcres
Faux snakeskin polymer clay cane by adena Plastelina.
Image for Free Polymer Clay Vase Tutorial
van FIMO blauwe ogen maken Blue iris eyeball - designed for polymer clay but I'm seeing fondant (for halloween cakes)
Pansies and violets from polymer clay. she loved pansies
Tuto cane kaléïdoscope 3
Sue - great pic tute for ombre effect
DIY Polymer-Clay-Pansy - could also make them out of gumpaste.
Imitating agate (Polymer Clay Daily)
The UK's Claire Wallis intrigues us with another smoothly blended cane. This time her cane layers imitate a blue lace agate geode. Made into a small brooch, it cradles a small pocket of crystals in its heart. Claire's recent Water and Lightning [.
Kerstin Rupprecht's photo tutorial, IN GERMAN, on making eye iris canes
Making and using various basic polyclay canes (in French but images are self-explanatory)