The only requirement being it must contain something made of metal or metal based so for example you could use metallic paint, embossing powders, metal embellishments, eyelets & staples.
Can't wait to see what you come up with.
My example:
Tag with Moo
The Moo is painted gold and has gold embossing powder sprinkled on it as well as a dragonfly brad. The tag is edged in gold embossing powder & has gold ribbon attached.
