Hi Halley-

Any of the mixtures that uses perlite or vermiculite would give you a pretty light end product, as long as you didn't use alot of sand in the mix. Since you are creating a wall hanging instead of a stepping stone, strength isn't as big a consideration as weight is. Check the faq here and you should find lots of choices in lightweight aggregates and mixes.

You can embed eyebolts in the sides of your casting to which you can attach wire after a full cure has been accomplished. Just make sure they're straight across from each other to make leveling your piece easier.

Jo