Originally Posted by

**lewisje** Any book on complex analysis or "complex variables" or "theory of functions" (even older term) should be a good starting point for learning about complex numbers.

I wonder though, when you say "complex envelopes" are you talking about envelopes of families of complex manifolds: manifolds derived from a metric tensor on C^n for some n? If so, you may also want to read up on differential geometry, geometric function theory, several complex variables, complex differential geometry...