Alberti’s scientific and rational conception of nature did not prevent patrons and artists in later Quattrocento Italy from admiring paintings for their more obvious charms of naturalism, pleasing design and skill. Landino, after all, had praised Masaccio as ‘a good imitator of nature’, and when a knowledge of the prestigious Flemish ‘ad olio’ technique began to reach Ferrara and Venice in the middle of the century it was eagerly adopted by northern Italian painters
like Cosimo Tura (before 1431—95) and Antonella da Messina (d. 1479), and, later, by Florentine artists such as Antonio del Pollaiuolo (c. 1432—91), both as a direct and rapid method of working, and as a technique which could transform the opacity of fresco and tempora — the equivalent of painted sculpture — into real textures, reflective surfaces and effects of landscape distance unprecedented in the art of Masaccio and his contemporaries. And in Giovanni Bellini (c. 1427—1516), the greatest Venetian painter of his day, ‘still the supreme master’ as Durer called him in 1506, the perspectival rigour and sculptural rilievo of Masaccio was combined with Netherlandish oil technique to elevate light — a colour-saturated light as translucent and vibrant as Venetian glassware — to the primary and immanent element of all creation (plate 18).
Bellini’s empathetic and poetic response to nature stands in marked contrast to Alberti’s search for the laws of mathematical harmony that structure the world and our perception of it. All three of his treatises centre round problems of optics, mathematics and perspective. De pictura was the first proper formulation of Brunelleschi’s single-point perspective. De statua tested the Polyklitan and Vitruvian proportions of the human body against empirical observation and created a new scientific canon of proportion — a canon extended by Durer and Leonardo, and given scientific, anatomical depth by the first artists’ dissections of corpses by Michelangelo and Leonardo in the early sixteenth century. In turn, Pollaiuolo’s various renderings of the Labours of Hercules (plate 15) amount to a manifesto of his ambition to become, in Leonardo’s words, ‘an anatomical painter’, for they achieved a new level of naturalism in the depiction of the male nude body in varieties of violent action. De re aedficatoria centred around the proper ordering of city life, in terms of functional decorum, and of mathematical beauty, for (borrowing Protagoras) man is the mean and measure of all things, and (borrowing Vitruvius) the proportions of the human body can be best identified in buildings and parts of buildings. Alberti’s neo-Stoic aesthetics merged with a neoplatonic cosmology which saw human proportion as a microcosm of the musical and heavenly harmonies which order all creation. The observation of the Franciscan mathematician, Luca Pacioli, friend of Piero della Francesca in Urbino and Leonardo in Milan, that the human body ‘contained all the ratios by which God reveals the innermost secrets of nature’, is the counterpart of Vitruvius’s diagram (drawn by Francesco di Giorgio and by Leonardo) of a man with extended arms and legs placed in a square or circle. The geometric lucidity of much Quattrocento church architecture (from Alberti’s unfinished Tempio Malatestiano in Rimini to Leonardo’s drawings of centralised churches), and particularly its emphasis on the dome and the circle, crystallises this cosmic-corporeal harmony. In contrast to the real, medieval, untidiness of most Quattrocento cities, the ideal townscapes painted at Urbino for Federigo da Montefeltro, with their rigorous perspectives and perfectly proportioned fagades, remain the purest reflections of Alberti’s ideal of civic-cosmic order (plate 19).
Piero della Francesca (c. 1420—90), who worked for some time in Urbino, distilled this clear and dignified world into figural art. For Piero, mathematics offered the key to understanding much of what the later Quattrocento meant by ‘nature’. His textbook, De abaco, provided merchants with a mundane tool for the calculation of cubic capacity. His treatise on perspective, Deprospectiva pingendi, offered mathematicians (like his pupil Pacioli) the most theoretically precise definition of spatial projection. And for artists, that treatise underlined the specifically mathematical value of commensuratione (the proportional relations of figures in space according to perspectival rules) as a central skill in painting. But in the last resort, the ‘truth’ of painting, for Piero and for most of his contemporaries, went beyond mathematical exactitude. In his understated colour harmonies, and his solemnly natural figures - all enveloped in a crystalline daylight — mathematics is subsumed into the symbolic, the epic and even the rustic (plate 20).
Leonardo da Vinci’s (1452—1519) single-minded identification of art with knowledge — demanding from the artist both an encyclopaedic grasp of nature and a mastery of the theoretical rules for its proper representation — extended Piero’s investigations into a complete cosmology. Overstepping the traditional boundaries between the various arts and the scientific disciplines, Leonardo’s art (particularly his drawing, which he elevated into a new tool of research) became at once the instrument of knowledge and the summit of all theory: ‘Painting . . . compels the mind of the painter to transform itself into the mind of nature itself and to translate between nature and art, setting out, with nature, the causes of nature’s phenomena regulated by nature’s laws.’ The consequences of this obsession with process and impersonal principle are evident in Leonardo’s output. Because intellectual mastery far outweighed technical realisation, the work of art often remained unfinished once its theoretical (essential) problems were solved. And as the artist uncovered nature’s secrets, so he came closer to the mind of God himself. Alberti had already called the artist alter deus. Durer characterised artistic activity as ‘creating just as God did’, and in 1500 — in a spirit that hovered between self-glorification and the Imitatio Christi — he painted a self-portrait in the startlingly frontal and hieratic pose reserved for kings and for Christ (Munich, Alte Pinakothek). Leonardo elevated the painter to ‘signor e dio’. In this deification of the artist lay the germ of the post-Romantic worship of artistic genius. What separated Leonardo from his contemporaries was his denial of the didactic value of history, and particularly of Antiquity, at the very moment when Botticelli and the young Michelangelo were reappraising the lessons of the Tuscan and antique past for the creation of a new culture. Against Leonardo’s Aristotelian fascination with the multiplicity of creation must be placed the neoplatonic belief — shared by many Florentine artists of Lorenzo the Magnificent’s circle in the final decades of the century — in the powers of artistic invenzione, and in the kinship, not between art and science, but between artist and poet.