I giochi del disegno. Forma, costruzione e proliferazione nei pattern chiusi dai rosoni del duomo di Milano.

The terms ornament and decoration, often used interchangeably, express similar concepts with different meanings. According to the dictionary, the first tells "the elements (friezes, frames, bas-reliefs, gilding, stuccos, frescoes, marble flounces, wallpapers, etc.) that embellish the external or internal structure of a building, breaking up its nudity and monotony". In classic architecture, the decoration arises from the needs of the construction, which conditions the formal archetypes. There is an intrinsic decoration in the building. It manifests in the relationship between the signs left by the joining of the constructive elements and the wise principles of ornament. These refer to ordered repetition, depending on rules deduced by the regular conformations of nature, with the combinatorial possibilities of the same four elementary symmetries at the base of the geometric principles of decoration. Nineteenth-century mathematicians and ornamental grammars describe the rules of drawing and the associative modalities of basic patterns, which refer to modular multiplication or circumference division. The topic refers to the plane tessellation and reflects the principles of contemporary Design Theory. At the end of the XIX century, the Polytechnic culture set the teaching of design on the same rules of ornamental grammar. Hundred years later, the developments of digital representation gave a new life to the integration between decoration and construction with the development of textile applications in architectural surfaces, decorated in their being. Digital technologies open new paths to representation and production, joining the thinking and the making actions in a sole process that solves complexity. That gives growing relevance to decoration patterns, which contemporary aesthetics lived contradictory, alternating the rational exaltation of constructive rigor and the exaltation of ornamental design. Their constructive regularity coexists with the possibility of drawing and texturing surfaces as an effect of their properties. The gothic design shows good examples of structural decoration. The rose windows in the Milan Cathedral have different articulations in size, radial divisions, and symmetries with a limited number of both angular and radial divisions. The research focuses on the rose's pattern rules. The aim is to apply generative computation to using closed patterns in open surface tessellation. Starting from the symmetries of the dihedral rose windows, visual computation produces available solutions in the creation of parametric patterns. Overcoming the specific limits of the periodic aggregation of circular modules with constructive applications at all project scales, they underline that decoration can still be the matrix of surface design.