I'm not sure what you want to emboss or if we're talking about the same thing but...
For paper I've used this thing called the "ShapeBoss" by Fiskars from Wal-mart. It has templates with designs cut out-like stencils. But there are 2 of the same template-you put the paper in between and press down on the design with a blunt edged pen or something similar-like the end of a small paintbrush.
And that's it-no heat for this-you have a cute design "pressed" into the paper. You turn it over so the design is raised for cards or whatever. This would work the same for soft metal-like copper or aluminum I suppose.
I've used this on cards and invites and it's very cool and EASY.
My SIL is getting into the other type of embossing with the special ink raised on the paper-that does require heat-she has a special "heat pen" but I don't know much about this.
Good luck,
Ann