During the 1st century, the use of bolster ashlars was a hallmark of Roman architecture. The shaped stone gives the parietal surface a volumetric outcome with greater monumentality and, at the same time, creates a light and shadow effect that changes throughout the day, with different visual results according to the sunlight exposure. The plastic and visual expressiveness, combined with the different textures created during the construction process, prompted a renewed interest in Italian architects at the end of the 15th century. The Palazzo Medici, by Michelozzo Michelozzi, the Palazzo Pitti, by Filippo Brunelleschi, and the Palazzo Strozzi, by Benedetto da Maiano, are some examples of the use of this decorative resource as a way of providing grandeur to buildings.
During the artistic development, the rustic and large-volume masonry was reduced in scale, regularized, and gained a purer geometric expression, becoming represented as a quadrangular pyramid. One of the most iconic examples is the Palazzo dei Diamanti, designed by Biagio Rossetti, which entire façade, covered with this ashlar pattern, suggested its name. In Portugal, influenced by Italian models, the best-known case is the Casa dos Bicos in Lisbon, built in 1522, with a project attributed to the architect Francisco de Arruda.
The use of the diamond pattern was not limited to the application on the façades of noble houses, and, in the last decades of the 16th century, it gained prominence again through the transference to tiles, this time for the interior decoration of religious areas. According to the historian Santos Simões, the pattern of “clavos” would have been first made in the potteries of Talavera, then later produced in Seville, from where it was imported for the decoration of the Jesuit church of São Roque, in Lisbon, in 1596.
The principal decorative motif tile forms a pyramid, with the top sectioned and filled with a vegetal element. This central decoration can gain some variation, but the most common version is a floret with eight ends, with a fuzzy sensation of movement caused by the small petals. On the diamond, the contrast between white and blue highlights the three-dimensional form of the design, which distinguishes it from the traditional pattern tiles produced in Lisbon in the 17th century.
The diversity of the ornamental motifs is such that it would be better to describe the pattern as a decorative family rather than a simple set of variations made from an initial base. Over the years, the pattern receives frames, flowers, and geometric combinations. In some cases, the pyramidal shape was replaced by an egg-shaped ornament or a pyramid with a triangular base accompanied by vine leaves.
In the last decades of the 19th century, the pattern returned to decorate the façades of Portuguese urban buildings. Once again, in the 20th century, the painter and ceramist Manuel Cargaleiro used it in the Lisbon metro station of Colégio Militar, reinterpreted with the addition of symbolic and mundane elements.
SIMÕES, João Miguel dos Santos. Azulejaria em Portugal nos séculos XV e XVI. Lisboa: Fundação Calouste Gulbenkian, 1979.
TOUSSAINT, Michel. Significados do azulejo na arquitetura. Portugal. Século XX, in O azulejo em Portugal no século XX. Lisboa: Comissão Nacional para as Comemorações dos Descobrimentos Portugueses, Inapa, 2000, pp. 239-255.