Help with making a mold?

Ok so i want to make a mold. I have the basics down....

Make a mold box, put subject in mold box...pour solution, acrylic, RTV etc...

My question is that what i want to do is take the object and make a mold of just the outside of it...so it is just a 'shell' of the original piece and hollow completely inside....kinds of like an armor that would fit perfectly over the original piece.

The end result would be that the original piece would fit perfectly inside the relplica piece that i want to create.

Any ideas on how to do this?

Thanks Guys.

don

This post edited by dsedy 11:15 AM 09/12/2008