They start as clay sculptures onto which two- (or more) part molds are made in order to reproduce all the details.
ðeɪ stˈɑːɹt æz klˈeɪ skˈʌlptʃɚz ˌɑːntʊ wˌɪtʃ tˈuː ɔːɹ mˈoːɹ pˈɑːɹt mˈoʊldz ɑːɹ mˌeɪd ɪn ˈɔːɹdɚ tə ɹᵻpɹədˈuːs ˈɔːl ðə diːtˈeɪlz.