To make these works it has been necessary to involve the dirt of the streets, the tyres of cars or the soles of the shoes of anonymous pedestrians (unaware of their essential participation in the creation of a work of art), the course of the time and the unpredictable atmospheric conditions. Chance, therefore. But also the relief of the sidewalks or the roughness of the road in different points of the city; and of course the decisions of the artist. They all contribute to create its extraordinary texture and subtle colour, hard to get by other means.