Hi Caro,
I am not an expert but did my dissertation on 'Mask and the Actor' and have some references that you may find useful. I am not a primary source however but some of the resources I found may lead you to a primary source. Chris Vervain and David Wiles may be your best bet, if you can contact them and get them to be primary sources. The references that you may find useful are:
Coldiron, M. (2002) "Masks in the Ancient and Modern Theatre, New Theatre Quartely, Volume XVIII, Part 4 (NTQ 72), (pp393-394) - Cambridge University Press
Marshall, C. W. (1999) "Some fifth-Century Masking conventions", Greese & Rome, 2nd Ser,k Vol 46, No2, (pp(188-202) - The Classical Association
Vervain, C. (2004) "Performing Ancient Drama in Mask: the case of Greek New Comedy", New Theatre Quarterly, Volume XX, Part 3, (NTQ 79), (PP245-264) - Cambridge University Press
Vervain, C. & Wiles, D. (2001) "The Masks of Greek Tragedy as Point of Departure for Modern Performance", New Theatre Quarterly, Volume XVII, Part 3, (NTQ 67), (pp254-272) - Cambridge University Press
Wiles, D. (2001)" Greek Theatre Performance - An introduction", 2nd Ed, Cambridge University Press.
I hope this helps.