From Wikipedia: For Joop Sanders' 1960 exhibition at the Stedelijk Museum, critic Thomas B. Hess wrote the following.
"It was in 1948 that I first met the advanced painters and sculptors who a decade later were to become famous as the “New York School”. And it was then that I was introduced to Joop Sanders and I was told that Joop was painting in a new style. Later I saw his pictures in some of the huge lively exhibitions the artists themselves organized in empty lofts and stores (no one in New York with the exception of Pollock was selling any paintings). At the time Sanders was obviously influenced by de Kooning and as it turned out this influence was the healthiest, the most open and stimulating of the moment as many of Sanders’ young colleagues can testify. They went on to discover or invent some of the most original forms of the 1950s. Shortly thereafter Sanders went to Europe where, I heard, he was establishing a growing reputation."