In his 1766 Alchemical Catechism, Théodore Henri de Tschudi denotes that the usage of the metals was merely symbolic:
ɪn hɪz wˈʌn θˈaʊzənd sˈɛvənhˈʌndɹɪd sˈɪksti sˈɪks ælkˈɛmɪkəl kˈæɾɪtʃˌɪzəm, θˈeɪoʊdɚɹə hˈɛnɹi də tˈiːʃˈuːdi dᵻnˈoʊts ðætðə jˈuːsɪdʒ ʌvðə mˈɛɾəlz wʌz mˈɪɹli sɪmbˈɑːlɪk: