Koster's work balances on the border between design and autonomous work. When does an object become furniture, and when can furniture be seen as a work of art? And what are the consequences of this question of definitions on the interaction between object and spectator? To find the answers to these questions Koster creates synthetic casts of architectural fragments, spaces and bodies.

One of the most striking examples of koster's work is her version of the Porta del Paradiso by Lorenzo Ghilberti (1378-1455). During the final years of her education at the Royal Academy for the arts in The Hague she became fascinated with this monumental entrancepiece, of which the academy owns a reproduction. The original plaster cast was bought in 1921 by the former director of the academy, Mr. Scheurleer. Koster collaborated with the finest mouldmaker of the Netherlands, Oscar Paanen, to create a rubber cast of the inverted gates of paradise. To realise this challenging project they use a technique for rubber casting developped by Paanen himself. From this cast Koster created a stand-alone, horizontal and treadable reproduction. A piece of 'furniture' which simultaneously serves as a functional object and a new autonomous work of art. This approach allows her to re-appropiate the history of architecture, and to reconfigure the ornament to a physical, tangible presence in space. Her ambition is to use this technique to rediscover architectural history worldwide. koster's latest body of work, elements in time, is a continuation of these ideas. For it, she created playful rubber stools that take on the iconic shapes from the history of ornamentation.