For many years, he led this society, starting as chairman and later serving as treasurer. Hesselius was also a member of the Federation Council for ten years and served as vice president for several years. He devoted much time and energy to showcasing the work of fellow artists, organizing exhibitions in Amstelpark (1975, 1978, and 1981) as well as in the Noorderkerk and Westerkerk.
Along with other members of the Dutch Circle of Sculptors, he co-organized exhibitions in Den Helder, Lochem, Roosendaal, Wageningen, and on the "Midwood Route." "Creating a joint play with works, building a total theater—this is undoubtedly creativity, but in space." He has been actively involved in organizing the Heineken Gallery in Amsterdam for over 25 years. He is responsible not only for selecting artists but also for overseeing and arranging exhibitions.
Hesselius' paintings from 1972-1974 went through a certain evolution, which ultimately led to the completion of this phase. Geometric frames became increasingly important compared to the expressive brushstrokes. When these frames finally defined the entire painting, Hesselius believed he had taken the final step.
In 1974, Hesselius stopped painting and fully transitioned to sculpture. Alongside his works on two-dimensional surfaces, there had always been sculptural pieces; early on, these were plaster and wire sculptures. After a period (around 1965-1966) of creating sculptures from scrap metal, he decided in 1971 to start working with more durable steel, cutting shapes autogenously (i.e., with gas) from sheets. From about 1972 to 1974, when his paintings became defined by geometric frames, Hesselius changed the direction of his sculptural work.
Playfulness and openness gave way to clear simplicity and mathematical precision. He reduced the form language to strict minimal abstraction and limited the color palette to white and sometimes light yellow. A series of monumental works emerged (including two commissions for Martin Luther King Park in Amsterdam in 1972 and for the Ford/Entam office in Amsterdam in 1974) that were closely connected to his paintings. Here, too, geometric, open and closed frames are present, now three-dimensional, in the form of intersecting beams.
Due to their rigid industrial appearance and precise construction, these works seem associated with minimalism. However, through their titles, Hesselius linked his works to human actions or the situations they embody. For example, the sculpture with yellow horizontal beams rising upward along vertical beams relates to forms of growth, sometimes fast, sometimes slow. Themes such as equilibrium, balance, and carrying are often present in his works; the process of creating sculptures is a slow one, starting with a theme or concept.
"For me, the process of creating a sculpture is important," says Hesselius. "First comes the idea, the thought, then the first movements in space, then the cutting and shaping of all the details that can contribute to the whole. Then comes the moment when you consider the work complete. And finally, the transfer—this is the essence."
The craftsmanship of sculpture plays a crucial role for Hesselius. Although he was self-taught as a sculptor, he has always been responsible for the design and execution of his sculptures. He never delegates the execution to anyone else because he wants the ability to make changes at that stage. To produce large steel sculptures, he built his own workshop in 1978 and equipped it to work with various cutting and welding techniques, such as plasma cutting, autogenous, electric, and CO2 welding.