He began by checking a Japanese-Dutch dictionary and a Dutch-English dictionary, and then went on to a modern Dutch dictionary that explained the usage of the colonial period. When he couldn't find a word, he turned to the Oxford English Dictionary, which includes etymologies of words in Western languages and provided him with useful leads on the many foreign loan words in the Dutch of the period.
曹永和查起字典可謂上窮碧落下黃泉：先查日蘭辭典、荷英字典，然後查用現代荷文解釋古荷蘭文的荷文字典，如果還查不到，再去查牛津大字典，因為這部大字典裡收錄了西方語文的字源，古荷蘭文中也有不少外來語，可以藉此找到有用的線索。