Expanded separation portfolios ( Se ) and Treasurer's portfolios T( Se ) are a sect of themselves. They arise out of risk-free assets and risky portfolios like other mutual funds. But their distinctive features set them apart from the common lot. This paper puts forth, firstly, a down-to-earth axiomatic that allows a complete formalization of the class of Se portfolios. Secondly, simple separation portfolios are featured and their differences with ( Se ) are highlighted. Next, the category of T( Se ) will be defined and their main properties brought to light. Last of all, there will be an expansion on the building of financial synthetics by means of enlarged separation portfolios.