Wulff studied crystal growth processes and modified Curie's principle on the minimization of surface energy. Now called the Gibbs-Curie-Wulff principle it states that the growth rate of the faces of a crystal are proportional to the specific surface energies of the faces. This is further extended by his idea of Wulff vectors and the Wulff construction. He also introduced a stereoscoping projection method using what is called the Wulff net. Wulff was one of the first to experiment with X-ray crystallography. He developed a relationship in X-ray diffraction (nλ = 2d sin θ) which was also found independently by the Bragg father and son duo in 1913 and sometimes called the Bragg–Wulff equation. The mineral wulffite are named after him.