Objective: How do you create a soap dish mold?

Which of the following solutions is more sound in terms of naive physics reasoning?

Possible answers:
[a]. Take an existing plastic soap dish. Cover with concrete and let harden. Apply heat to melt the plastic dish and drain..
[b]. Take an existing plastic soap dish. Cover with molding clay and let harden. Apply heat to melt the plastic dish and drain..
[b].