I've made both elements of this pendant from metal clay which I have then fired in my kiln to be left with a perfectly pure piece of metal. This one was made using sterling white bronze. The rectangular part has been textured with a texture plate and the little heart has been left plain for contrast.  The chain is made from a silver toned base metal.
 
The length of the necklace is 18 inches / 45cms and the pendant is 1.25 inches / 3.25cms in length