When Klaas first became interested in visual art, he drew inspiration from nature. He began sketching outdoors, and soon developed a preference for drawing trees, which he tried to depict as realistically as possible.
After a few years, he decided to broaden his horizons by taking classes at the Academy of Industrial Design in Eindhoven. After some time, his interest shifted from the realistic to the abstract. Initially, he painted large abstract paintings, but soon his works became smaller and more contemplative in nature.
Another constant in his life has always been his interest in music, especially classical music. He sought to express in his work the mood he experienced while listening. This often resulted in a series of paintings and gouaches that shared a similar atmosphere, all of which had a contemplative character.