Natural user interface (NUI) can be defined as human-computer interaction systems in which the user employs intuitive actions based on the human behaviour. Common examples of NUI interfaces are those ones that use multi-touch screens, gesture and sound recognition systems, and painting tablet devices. Paper marbling is a painting approach in which the artist uses proper tools - as combs and brushes - to interact with the paints deposited on an aqueous surface, producing thus marble-like paintings. These paintings are then transferred to an absorbent paper, which are used, for instance, as book cover. In this work, we present a computational marbling system that incorporate NUI to easy the generation of marbling patterns.