http://jmcolberg.com/weblog/2008/02/what_makes_a_great_portrait/
Research- Studio Portrait
What makes a good portrait

Portraits can define what work the person does and to construct reality rather than reproduce it, they densely coded such as ladder tights can  be meaning to them, might want to come out as different not looking perfect.

Portraits can challenge stereotypes we have on children, mothers and can explore issues of themselves.

Trying to pinpoint what really makes a good portrait is like trying to figure out why the person smiles at you and feels good. Portraits can become a great image when photographer creates a strong and moving story when viewed and furthers itself with great use of light, lines and framing. Photographers can make a strong meaningful portrait because subject and photographer are both willing to take a stand and make a statement about the subject. What strikes a good portrait can be a full visual combination of texture, light, expression, the eyes and regard of the subject and portraying a sense of  tense from the moment  and humour coming from the subject. The subject being vulnerable and looking awkward can be access  point for a viewer to point out humanity.