In the ancient Far East, natural bitumen was slowly boiled to get rid of the higher fractions, leaving a thermoplastic material of higher molecular weight that, when layered on objects, became hard upon cooling.
ɪnðɪ ˈeɪntʃənt fˈɑːɹ ˈiːst, nˈætʃɚɹəl bɪtˈuːmɛn wʌz slˈoʊli bˈɔɪld tə ɡɛt ɹˈɪd ʌvðə hˈaɪɚ fɹˈækʃənz, lˈiːvɪŋ ɐ θˌɜːməplˈæstɪk mətˈɪɹiəl ʌv hˈaɪɚ məlˈɛkjʊlɚ wˈeɪt ðˈæt, wˌɛn lˈeɪɚd ˌɔn ˈɑːbdʒɛkts, bɪkˌeɪm hˈɑːɹd əpˌɑːn kˈuːlɪŋ.