in vennootschap met zijn broer Christoph Frederik tot 1 mrt 1906, daarna met een derde vennoot August Morel. Jan Frederik stapt uit deze firma op 19 jan 1911.
leeftijd 54 jaar; begraafplaats Zorgvlied
(1) He is married to Anna Catrina de Graaff.
They got married on January 21, 1904 at Amsterdam , he was 25 years old.Source 3
Child(ren):
The couple were divorced from March 17, 1909 at Amsterdam .Source 4
(2) He is married to Marie Catharine Wilhelmine Elisabeth Brandt.
They got married on August 11, 1910 at Amsterdam , he was 31 years old.Source 5
Child(ren):
Jan Frederik Jacob Jonkhart | ||||||||||||||||||||||||||||||||||
(1) 1904 | ||||||||||||||||||||||||||||||||||
Anna Catrina de Graaff | ||||||||||||||||||||||||||||||||||
(2) 1910 | ||||||||||||||||||||||||||||||||||