Because of the great power it emenates, the port of Rotterdam is the artist's main source of inspiration.

There she found an abundance of forms in primarily unflexible materials such as iron and steel; anchor-wiches, davit's, bolders, cranes, the poop of a ship etc. are the subjects of her prints. In silk-screen Calis was able to achieve full artistic potential. Graphic perfection was of paramount importance to her: all her work was hand-made in her own workshop and printed in very limited editions.