In the late summer of 1912 Jan Sirks advertised for a “Clothed Model”. Hillegonda Mol spotted the advertisement,quite by chance,in the Rotterdam daily newspaper. She was a highly accomplished pianist in need of funds for an upright grand piano and saw this as an opportunity to make some money.It was highly inappropriate for a young woman of her milieu to do such a thing so she initially kept it a secret. Somehow,her stepmother Johanna,with whom she did not get on,found out about it.Johanna told Hillegonda’s father but failed to admit that the advertisement had stated “clothed”. They unsuccesfully tried to stop her.
Hillegonda posed for Jan for several weeks and then told him that she thought his work was so good that it ought to be sold. Sirks found that highly amusing and laughed aloud. This moment changed their relationship forever as Jan confessed his love for her and Hillegonda became his agent. In turn for her work Sirks bought Hillegonda a Bluthner upright grand. They were engaged in 1915 and were married on 15 June 1916. Sirks painted,etched and drew Hillegonda throughout his life.