We apply the concept of "island formation" established for planar substrates, where ligands laterally cluster as they adsorb, to preparing nanoparticles (NPs) with precisely sized surface patches. Using gold triangular nanoprisms and 2-naphthalenethiols (2-NAT) as a prototypical system, we show that the preferential adsorption of 2-NAT on the prism tips leads to formation of tip patches. The patches are rendered visible for direct transmission electron microscopy and atomic force microscopy imaging upon attaching polystyrene-b-poly(acrylic acid). Using this method, the shape of patchy prisms is varied from small lobed, big lobed, trefoil, T-shaped to a reuleaux triangle by increasing the 2-NAT-to-prism concentration ratio. This trend matches with predictions of island formation as elucidated by our self-consistent field theory modeling, from which we exclude Langmuir adsorption. The tip-patched prisms assemble into unexpected twisted dimers due to the patch-patch interactions. We expect the island formation as a generalizable strategy to make patchy NPs of various shapes for emergent assemblies and applications.