i was first introduced to this technique by watching Sarajane Helm's masks. I wrote this tutorial a few years ago and was is a better time to take off the dust than Purim? :-)
here is another tutorial written by Israela Angel for makink a polymer clay mask on a plaster armature http://www.art1.co.il/instructionsteps.aspx?wid=78a873b1-e734-4cf0-b608-9430722e849d
my friend Maskit uploaded to her blog some links for mask tutorials - if you read hebrew check this post too.
Barbara McGuire shows how to make this mask on HGTV
the craftgossip showcased a mask gallery which is very inspiring.
did all these tutorials made you want to make masks? do you already make pretty masks? Sarajane is seeking for masks for a potentail new book she is working on. click here for more details.