You will need oven bake clay, like fimo in black, silver, turquoise and gritty sand.
Then roll it out into a long thin snake.
usually about 15 minutes at 275*F
I love to see the shimmer of the silver in their...and the cool veins.
You could glue things right on top of them...like steampunk cogs and wheels...flowers or cabochons...or even a cameo!