#dutch
Siersma is the maiden name of his wife: Tjalke Koene née Siersma
https://archief.amsterdam/indexen/deeds/98517a9c-6df6-3112-e053-b784100aeeb7?person=98517a9c-6df7-3112-e053-b784100aeeb7
https://www.openarch.nl/saa:5f13ab1e-e0af-48cc-980f-c7b1ec887123