8
The Idea of a Book on Painting
In the Renaissance, art was not created to express an artist’s personal feelings or ideas. It was commissioned by patrons to serve specific purposes. Patrons decided what artists would depict. Luckily, patrons could not control how artists chose to interpret the subjects that were selected for them. Indeed, artists were constantly revising traditional interpretations of famous subjects and finding new techniques to differentiate their works from those of their peers in the ferociously competitive art scenes of Florence, Milan, and Rome.
Occasionally, artists were able to carve out time to create works that no patrons had commissioned but that reflected their personal interests. Typically, these were small works that did not require huge investments of time and materials. Renaissance artists also wrote books on their art, and while they often sought the favor of a patron for their books, they did so after they had already written them. In a way, the writings of Renaissance artists were some of the best examples of art (albeit not paintings or sculptures) made outside of the patronage system.
Like any Renaissance artist, Leonardo worked within this system of art patronage. His paintings were meant for confraternities, dukes, merchants, religious orders, and governments that told him what to paint, although not how to paint. But unlike most of his peers, he was extraordinarily successful at setting aside time for his own interests, especially when he worked for the duke of Milan. In that city, in his large workshop in the Corte Vecchia, surrounded by a small but devoted group of assistants, enjoying the luxury of continuous employment over an extended period of time, he was able to “express” himself and to start work on his book. And not just a book, but a book for painters—a book about how philosophy and science would transform them into great painters.
We can identify the period when Leonardo started to convert his thoughts on art into book form. It was between 1489 and 1491. Leonardo was about forty, a mature artist, and the head of a hectic workshop. Leonardo called it “my factory,” la mia fabrica, nearly five hundred years before Andy Warhol called his own studio “the factory.” Leonardo’s factory was incredibly busy, and yet the artist somehow found time for his book. He was determined to write it.
Let me give you a sense of how busy Leonardo’s factory was. He got involved in architecture, no doubt thanks to his friend the ducal architect Donato Bramante, and even submitted a proposal for the tower that would crown Milan’s cathedral—though he withdrew from the contest as he was not qualified to build it. Nonetheless, the experience gave him the opportunity to think about the relationship between architecture, the human body, and the cosmos. He wrote that the “ailing cathedral” needed “a doctor-architect” who knew “what are the causes whereby the building is held together, and is made to endure.” He sketched churches with round, polygonal, or cruciform plans in a quarto-sized notebook (known today as Manuscript B), again following the example of Bramante, who had designed such churches as the ducal architect (Bramante also designed the dome of Santa Maria delle Grazie, next to the refectory where, later, Leonardo painted the Last Supper).
Leonardo also sketched water pipelines for the duchess’s bathroom and imagined new urban structures to minimize contagion during pestilence outbreaks. (A devastating one had swept through the city in the winter of 1485.) He became interested in Vitruvius’s book On Architecture, and in order to understand it better he befriended several experts on Vitruvius. He also worked on a monumental bronze equestrian statue representing Ludovico’s father.
He designed sets and costumes for court festivities, and on January 13, 1490, he dazzled the court with a stage set for the Feast of Paradise, a play that was to be performed at the celebration of a ducal wedding. Beams of colored light, projected through tinted glass, cast moving shadows on the walls around the hall. The light emanated from a golden globe with lamps suspended inside.
Leonardo painted, too, of course—but because demand for his work had increased so dramatically, he filled his factory with partners and assistants who helped him out. Some did more than help, in fact.
Several accomplished painters, such as Marco d’Oggiono, Andrea Boltraffio, and Andrea Solario, who had joined Leonardo’s workshop as fully formed artists, were by and large responsible for the works that came out of the factory. Leonardo had taught them his way of painting, and they had become proficient at making small devotional images, altarpieces, and portraits based on his drawings and executed in his style. He supervised them and occasionally added finishing touches here and there, but these artists did the bulk of the painting. This may seem like a form of deception to us today, but in the Renaissance a work by a master was a work based on his design, made in his workshop, and executed under his supervision. It was not necessarily a work the master painted from beginning to end.
Other young boys came to Leonardo’s workshop to be trained. One, Gian Giacomo Caprotti from Oreno, joined in 1490 at age ten and would remain with Leonardo until the master’s death, but when he arrived he was more trouble than help. In less than a year, he managed to steal valuable tools from other assistants, money, and “Turkish leather to make boots” from Leonardo, as well as money from Leonardo’s patrons—not to mention the copious amounts of food and wine he consumed. Leonardo called him “thief, liar, obstinate, and glutton” and nicknamed him Salai, after the name of a little devil in a famous epic, Morgante, written by the Florentine Luigi Pulci. But Leonardo kept him, as he had become very fond of this handsome boy. Salai even became Leonardo’s lover.
In short, Leonardo’s factory was a busy place in those years, and a tough place to work. Leonardo supervised everything and everybody, but he played favorites, too.
He himself painted only works commissioned directly by the duke, such as the portrait of the duke’s mistress, Cecilia Gallerani.
He represented the young lady with a slight twist to her body, to show that her attention had been caught suddenly by an unseen visitor (the duke?). She holds an ermine, which is a pun on her name—galee is the Greek word for “ermine” and the root of her family name, Gallerani. But the ermine was also a symbol of purity because, according to a popular belief, the animal would rather die than dirty its white coat. It was also one of Ludovico’s emblems, and so a proxy for the duke. The portrait came out so well that a court writer claimed that nature itself was envious of Leonardo because he portrayed one of nature’s stars; for this writer, Leonardo was “the Apelles brought from Florence,” a nod to one of the most famous painters in ancient Greece.
For another court portrait, La Belle Ferronnière—which most likely represented another of Ludovico’s mistresses, Lucrezia Crivelli—he created stunning reflections that bounce off the lady’s red dress and onto her right cheek. As he wrote in those years: “Every object devoid of color in itself is more or less tinged by the color [of the object] placed opposite. This may be seen by experience […] if the surface thus partially colored is white, the portion which has a red reflection will appear red […].”
Optics was as central as ever to Leonardo’s thoughts in those years. The connection between optics and art had received a major, unexpected boost a few years earlier, on March 16, 1485, when Leonardo witnessed a total solar eclipse. He observed it with a rudimentary tool he himself had made: a sheet of paper he had pricked with a needle to create a small hole through which to observe, without hurting his eyes, the shadows and reflections created by the moon covering the sun. But what interested him was not the total eclipse in itself, but rather the optical effect of the moon seen against the backdrop of the sun. “The moon,” he wrote, “though it is at a great distance from the sun, when, in an eclipse, it comes between our eyes and the sun, it appears to the eyes of men to be close to the sun and affixed to it, because the sun is then the background to the moon.”
Backdrops meant a lot to him as a painter. He had learned from optical books that our perception depends a great deal on the background against which the edges of an object terminate, and if he read Alhacen’s book he was familiar with innumerable such examples. He himself wrote that “no visible object can be well understood and comprehended by the human eye excepting from the difference of the background against which the edges of the object terminate and by which they are bounded.” He translated these theoretical ideas into practice when he painted human faces against dark backgrounds: Ginevra against a juniper bush, Mary against rocks. Rarely did optics and art come as close in Leonardo’s mind as they did on that day in 1485 when he observed that total eclipse through a pinhole on a sheet of paper.
In those years, he was deliberate in his search for books. He knew exactly who owned the best and rarest books in Milan, as perhaps he knew as a youth who owned them in Florence. “The heirs of Maestro Giovanni Ghiringallo have the works of Pelacani”—Pelacani was an Alhacen expert and the author of optical books. “A grandson of Gian Angelo’s, the painter, has a book on water which was his father’s.” “Messer Vincenzo Aliprando, who lives near the Inn of the Bear, has [the copy of] Vitruvius once owned by Giacomo Andrea,” an architect and an expert on Roman architecture whom Leonardo used to visit with his assistants. Leonardo reminded himself to “Get the friar di Brera to show you ‘de ponderibus’”—this is Euclid’s book on mechanics, a copy of which the physician Maestro Stefano Caponi also owned. “Ask Messer Fazio to show me di proportione,” a complex text on proportions written by al-Kindi, a ninth-century philosopher.
He went after the classic books on optics, Witelo, Pecham, and Bacon. He sought out Aristotle’s Meteorology because of its extensive discussion on the atmosphere.
He took field trips to scrutinize the effect of the atmosphere at different altitudes. He climbed the Monte Rosa, or Il Momboso, as he called the Alpine mountain between France and Italy, and observed that “the blueness we see in the atmosphere is not [its] intrinsic color” but the result of “warm vapor evaporated in minute and insensible atoms on which the solar rays fall, rendering them luminous against the infinite darkness of the fiery sphere which lies beyond and includes it.”
In the midst of all these activities, he was also determined to find time to work on his book on the art of painting.
It would not read like any previous art book. Over the years, he had collected recipes for mixing colors and varnishes, but his book would not be a “recipe book” like Cennini’s The Craftsman’s Handbook, which had been written about a century earlier and remained invaluable as a guide to how to grind colors and prepare panels. Nor would it be a biographical account of previous artists or a hodgepodge of quotations from optical authors along the lines of Ghiberti’s Commentaries, although he had learned a lot from that book, too.
Nor would it be an essay like Alberti’s “On Painting,” which was written in 1435 in Latin and Italian and was another book he read with great interest, although he got from it only very general principles. In fact, as noted earlier, Alberti had purposefully left out the most sophisticated parts of optics—“all the functions of the eye in relation to vision” as well as disquisitions on “whether sight rests at the juncture of the inner nerve of the eye, or whether images are represented on the surface of the eye, as it were in an animated mirror.” Alberti thought these topics were not essential to painting.
Leonardo begged to differ.
His art book would teach artists about natural philosophy and science, about how we see and know the world, and all he had learned concerning the soul, the senses, and the emotions.
As he read philosophy and science books, he had taken notes from those parts that seemed most promising to him and tried to rephrase them in his own words. But he was an artist writing for other artists, and even though his book included philosophical discussions, its strength would lie in its many pictures and diagrams. He predicted that “many will say that this is useless work,” but he regarded them as men who “possess a desire only for material wealth and are entirely devoid of the desire for knowledge [sapienza] which is the sustenance and truly dependable wealth of the soul [anima].” Instead, he planned to tell artists to “first study science [scienza], then follow the practice born of that science.” His view was that painters “who are in love with practice without science are like a sailor who boards a ship without rudder and compass.” Those painters have to, in essence, reinvent the wheel each time they pick up a brush, hoping that through trial and error they will come upon a breakthrough. Those painters might succeed, but they will never know how they did it. And they might not be able to do it again. But the artist who develops a deep knowledge of the science of optics, “the signpost and gateway” of painting, understands the rules—born from experience and the senses—by which the passions of the mind can be brought alive. That artist can use those rules time and again to confidently guide his work.
The book would also offer very practical advice. It would teach the modern painter that “narrative paintings [storie] ought not to be crowded and confused with too many figures”—he had learned this lesson the hard way with the failed Adoration. And it would teach that the modern artist has to draw from nature the lights and shadows on each muscle, but that he cannot be satisfied with this. Leonardo’s intention was to save his peers the efforts he went through to figure out that the core of art did not lie where everybody thought it did—in the narrative, or in the anatomy of the body, or in bright colors, or in the technical mastery of foreshortening—and that artists who painted figures that looked “like a sack of nuts rather than the surface of a human being or, indeed, a bundle of radishes rather than muscular nudes” were wrong. He did not mention any artist by name, but everybody knew whom he meant: the Pollaiuolo brothers. They were great artists, and they understood anatomy, but they were “wooden painter[s] [pittore legnoso]” because they did not recognize that anatomy and musculature did not lie at the heart of great art, but were only means to a greater end.
Art had to capture something else.
Leonardo tried to explain what he meant.
He jotted down notes about the “purpose of the soul” and about paintings in which the most praiseworthy thing is a figure that “best expresses through its actions the passion of its soul.” He wrote a draft, and then another, and then a third, but he crossed them out before finishing them. It took a while before he could find the right words to express what he meant:
The good painter should paint two main things, and these are man and the intention of his mind [concetti della mente sua]; while the first is easy, the second is difficult, because it has to be captured through the gestures and the movements of the limbs, and these should be learned from mutes, who better actualize them than any other sort of man.
He also drafted an introduction, which is indicative of his feelings at the time. Part of him was defensive and insecure: “I know well,” he wrote, “that, not being a man of letters, it will appear to some presumptuous people that they can reasonably belabor me with the allegation that I am a man without learning [omo sanza lettere].” He had no formal training in Latin and had never learned how to write an elegant essay with a beginning, a middle, and an end.
But another part of him was as assertive as ever. “Foolish people,” he called those who accused him of not having “literary learning” and being unable to “express the things I wish to treat.” Those fools “do not grasp that my concerns are better handled through experience rather than bookishness.” Experience as knowledge acquired through the senses had been Alhacen’s mistress. It also became Leonardo’s mistress: “Though I may not know […] how to cite from the authors, I will cite something far more worthy, quoting experience, mistress of their masters.”
In order to produce his book, Leonardo went digging through the mess of disorganized notes he had accumulated over the years. He must have spent days and days searching for the best diagrams and observations, which he copied onto new folios. He left these folios unbound in order to write on them more easily, but he organized them into sets (effectively loose-leaf notebooks), each on a different topic. In the span of two or three years, between 1489 and 1491, he filled pages and pages with notes on colors, shadows, and the atmosphere, and sketched dozens of optical drawings and skull and proportion studies. About two hundred pages and over one hundred diagrams have survived, but these may be only a portion of those he made. It was in these pages that he wrote that the illusion of relief created by shadows is “the soul of painting,” that “painting is grounded in optics,” and that optics is “a rational demonstration by which experience confirms that all things send their semblances to the eye by pyramidal lines.”
These folio sets were his working draft, and we have to imagine them stacked on his desk for months on end, readily available to him for revisions and additions.
As in a painting, he looked for the right spot for everything. Things had to be spaced just right, images had to be balanced with words, the shape of blocks of text had to be adjusted to the shape of drawings, and things had to be shaded impeccably.
The fact that many of these folios are so carefully planned—word and image are beautifully combined, drawings are highly finished, and some are fully shaded—indicates that they were advanced versions of notes and sketches Leonardo drafted earlier; how much earlier is a matter for debate, but I would speculate years earlier, perhaps as early as his years in Florence. Many shadow drawings seem like studies for Ginevra’s head, for details of the Adoration, and for the heads in the Virgin of the Rocks, for instance. Many notes on the atmosphere seem to explain the landscapes he had been painting since the 1470s.
Judging from Leonardo’s notes from those years, around 1490, it seems that he planned his book as a collection of short chapters, each with a title posing a philosophical question and a short text solving that problem step-by-step. Many chapters would be illustrated by images.
For example:
How shadows fade away at long distances.
Shadows fade and are lost at long distances because the larger quantity of illuminated air which lies between the eye and the object seen tints the shadow with its own color.
Or:
On the three kinds of light that illuminate opaque bodies.
The first kind of light which illuminates opaque bodies is called individual light [lume particulare] and this is the sun or any other light [coming] from a window or flame. The second is universal [light] [universale] such as we see in cloudy weather or in mist and the like. The third is composed [light] [composto], that is when the sun is entirely below the horizon, either in the evening or morning.
His book on painting would read more like Euclid’s Geometry or Alhacen’s Optics, and this fact alone would show that, like optics and geometry, painting was a branch of natural philosophy, and his art book was as authoritative as Euclid’s and Alhacen’s own works.
A folio set titled “On the Human Figure” was started on April 2, 1489.
Here, Leonardo gathered highly finished skull drawings and spaced them elegantly on the page, adjusting their accompanying text to the sketches’ shape and size. He drew each bone and eye socket so masterfully that one has the illusion of handling a real skull and feeling the textures and recesses of each bone. He drew them in a sagittal view, as if the skull had been sliced open and viewed from the side. This was itself something of a revolution, as nobody had ever thought of cutting skulls—or any other part of the human body—into two halves to distinguish left from right and to make their interiors visible. These skulls revealed the hidden scaffolding of muscles, which, in turn, provided the hidden structure of facial motions. But they also indicated exactly where the soul and the sensus communis, the organ that combines sensory data and gives us knowledge of the world, resided. Most artists had no interest in the location of the sensus communis, but Leonardo had learned from optical manuals that “the common sense is the seat of the soul,” the place where sensory experience is gathered and analyzed. His view of art as philosophy demanded that artistic training begin with a study of the workings of the soul, starting with identifying its location in the body. This was why he took the trouble of locating the “chamber” containing “common sense,” with cartographic precision, inside the head.
His ability to translate knowledge into images, to visualize even complex concepts, was unsurpassed, and nowhere was this more evident than in these stunning skull drawings. He also portrayed these skulls using yet another skill he wanted artists to master: proportion. Human proportions had always been of great interest to artists, even though each culture and time had different ideas on what perfect proportions were. Alhacen had considered proportion to be the second-hardest “visual intention” or characteristics of an object to judge (the hardest was beauty), but most Renaissance artists followed what Vitruvius said about proportions. The problem was that Vitruvius’s technical language was hard to understand, and that the many handwritten copies of his text were corrupted and inconsistent. A typical instruction from Vitruvius might read something like this: the distance between the eye socket and the chin equals the distance between the eye and the top of the head, which in turn is the exact half of the distance between the chin and the nose, or the distance between the nose and the eye socket. Vitruvius was not an easy read.
Being the great artist that he was, Leonardo made visible Vitruvius’s instructions with unprecedented clarity. He superimposed Vitruvius’s proportional division of the human face over his skulls, showing at a glance not only the location of the common sense but also the perfect proportions of the human head: nose, mouth, eyes, and forehead were proportionally related.
And then he went a step further than Vitruvius or any previous author of medical or optical texts had gone. He used the module, or unit, Vitruvius had used to measure the human face (Vitruvius had settled on one-third of its length) to place the chamber of the sensus communis inside the skull at one-third of the skull’s depth.
Leonardo’s famous Vitruvian Man, which was conceived in those same years, extended this exercise from the head to the whole body.
This pen-and-ink drawing, sketched in metal point on a large folio, has become an iconic image of Western culture, defining the relations between the universe and the human body. But for Leonardo this was only a draft, a personal summa of observations he had found in various Vitruvian manuscripts, each manuscript reporting different measurements due to the numerous discrepancies that appeared in handwritten copies. He transcribed the contradictory measurements, planning to rework them later and come up with a clean version of Vitruvius’s text. He never managed to combine Vitruvius’s words into a single, coherent passage, although he summarized Vitruvian proportions in a sentence: “a man opens his arms as far apart as is his height.” And he did visualize that sentence in a superb image of unique clarity.
In another folio set, which he had prepared using a blue wash, he captured the human body from within.
Anatomy was essential to understanding the force (forza), or motion (moto), that animates human beings. Similar to Aristotle, he called this force a “spiritual virtue” that flows “through the limbs of sensate animals, thickens their muscles, and whence these thickened muscles contract and pull with them behind the nerves with which they are conjoined, and from here the force of human limbs is caused.” He wanted artists to learn human anatomy—if they did not they “will accomplish little.” They had to know “which chord or muscle is the cause of such movement”—the muscles that close eyelids, raise eyebrows, part “lips with teeth clenched,” and bring “lips to a point”; even those that make people laugh, sneeze, and yawn, or express wonder, thirst, sleep, hunger, fatigue.
These notes on anatomy are highly illustrated. His illustrations made it possible for artists to learn anatomy without having to find a corpse, convince a doctor or at least a barber to flay and dissect it, and struggle to capture its various parts before fluids spilled all over or the muscles got out of place or the blood vessels decomposed. Not only did Leonardo make anatomical drawings more accurately than anybody had ever done before, but he also peeled the skin off of the bodies he drew in order to visualize the tendons and muscles underneath. A head study showed each muscle of the mandible, face, and neck located in its proper place, the view unobstructed by blood, the form unaltered by decomposition. There simply was no better drawing to study the movements of facial muscles—and therefore the underlying anatomical structures of emotions.
Alberti had suggested previously a similar approach to painting a nude: “sketch in the bones, then add the sinews and muscles, and finally clothe the bones and muscles with flesh and skin.” But Leonardo was the first to actually draw anatomy “in transparency,” turning Alberti’s generic instructions into a system for artistic practice.
At about the same time, he assembled another folio set, which he left untitled.
Here he gathered notes on colors and the atmosphere. He also included thoughts on the different arts—painting, sculpture, music, poetry—based on the senses they primarily engage—sight, touch, hearing. It would come to be known as Leonardo’s paragone, or comparison of the arts. Here, also, is his famous description of the human body as a microcosm:
The ancient called man a lesser world and certainly the use of this name is well bestowed, because his body is an analog for the world, in that it is composed of earth, water, air, and fire.
But the majority of this untitled notebook, known today as Manuscript A, dealt with painting as an activity that “embraces all the ten functions of the eye; that is to say darkness, light, body and color, shape and location, distance and closeness, motion and rest.” As discussed earlier, these were an adaptation of Alhacen’s functions of the eye. So much so that when Leonardo explained that “my little work [piccola opera] will comprise an interweaving of these functions” to help painters imitate nature with their art, he seemed to suggest that he thought of his book as an optical manual for artists—a sort of simplified “Alhacen for artists,” one might say.
He adapted to artistic practice Alhacen’s examples on the thickness of the medium, on distance, and on the intensity of light. Here is a note on reflected colors that demonstrates his use of optical literature, but that also brings to mind the reflected colors of his paintings—the blue reflections on Ginevra’s bust, the red reflection on La Belle Ferronnière’s cheek: “The painter,” he wrote, “must pay great attention in situating his bodies amongst objects which possess various strengths of light and various lit colors” because “the surface of every opaque body takes on the color of an object opposite to it.” Here is another on his famous smoky effects: “Note […] that your shadows and highlights blend together without hatching or strokes, in the manner of smoke [a uso di fumo].” In another passage he wrote that “shadows partake of universal matter” and asked a key question that shattered long-standing beliefs about painting:
Which is best, to draw from nature or from the antique? And which is more difficult to do, outlines or lights and shadows?
For him the answer was unequivocal: it is best to draw from nature, and it is more difficult to paint lights and shadow than outlines.
His advice was revolutionary. Florentine artists had worked to perfect their outlines, or disegno, for over a century, and Cennino Cennini had codified the practice in the early fifteenth century when he told artists in training to “Begin with drawing or outlines [dal disegno t’incominci].” His view had never been challenged. But Leonardo thought that there are no boundaries in nature: “The boundaries [termini] of two conterminous bodies are interchangeably the surface of each. All boundaries of a body are not parts of that body,” he wrote, adapting the teachings he had learned from optical literature and possibly from Alhacen. What the eye sees in nature are the blurred edges between things, and he wanted artists to render the mingling of colors and shadows at these edges with pigments and varnishes. If they did not, their works would have “a wooden effect [legnosa resultazione].”
Leonardo’s new art was about getting viewers to feel a certain way. It was about connecting real people to painted figures at a very deep level, having those who look at a work feel the same feeling that the painted figures felt—fear, terror, joy, or amazement. It was about transporting Renaissance viewers in time and place, giving them the illusion of moving in the same landscape or building where the painted events occurred, being immersed in the same atmosphere and light. This new art had to capture hazy contours, soft edges, indistinct thicknesses, smoky boundaries, reflected colors, misty air.
He told artists that if they wanted to move viewers, they had to master three kinds of perspective, each based on how things appear as they recede from the eye. Linear perspective, or prospettiva liniale, deals with “the reasons behind the diminution of objects” in terms of their quantity, or size, such as a building seen from afar or a tree line along a road. This was the perspective Renaissance artists were most familiar with, as Alberti had offered instruction on how to diminish the size of objects geometrically; his instructions, which were based on Brunelleschi’s perspective panels and on the practices the artist Masaccio adopted for his paintings, had become part of the training offered in workshops. The second and third kinds of perspective, perspective of color (prospettiva di colore) and perspective of disappearance (prospettiva di speditione) or aerial perspective (prospettiva aerea), were less familiar to artists, as Alberti had omitted discussions about color and the air. But for Leonardo, it was essential for artists to know “the way colors vary as they become more remote.” Aerial perspective was “concerned with how objects [in a picture] ought to be less detailed as they become more remote.”
Both color and aerial perspective are due to the intervening air, which for Leonardo was not inherently blue but took its color from a mixture of light and shade—that is, the light of the sun and the darkness of the atmosphere. For Leonardo, painters had to diminish the size of objects, soften the intensity of their colors, blend their details, smooth their boundaries, and tone down the contrast with their backgrounds according to universal rules that govern how we see.
A section of the planned art book would be devoted to light and shadows. In fact, this section was the most fully realized of all. Leonardo filled an entire folio set with highly finished light and shadow drawings, which, like his skull studies, he positioned carefully on each page, adjusting the size of the accompanying notes.
This set on light and shade, which is known today as Manuscript C, was the largest in size, the most advanced in its concepts, and contained the greatest number of diagrams of all the folio sets he assembled in those years (or at least among those that survived).
Here can be found specific instructions on how to draw with geometric precision “the convergence of shadow [rays] with light rays,” which always has “a mixed and blurred appearance,” as well as famous principles such as that “no object […] will ever appear separated from its background” and that “optics adds knowledge to things.” Here is Leonardo’s dictum to artists that painting is superior to the other arts because it is “the master and guide of optics.”
The diagrams were works of art in their own right, a fact the art historian and Leonardo expert Anna Maria Brizio described in one of the first studies dedicated to these shadow drawings: although these are just geometrical diagrams, they have “an airy lightness, a transparency […], a complex ‘radiant’ texture” that conveys “an extraordinarily vibrant suggestion of space and motion” thanks to how carefully Leonardo traced the multiple directions and intersections of light rays.
Some diagrams Leonardo enlarged to fill half a page, so as to make visible the blurred edges of shadows and penumbras with geometric precision—and not just the shadows and penumbras cast on discrete objects, which he called primary shadows (ombre originali), but also the shadows and penumbras cast on walls and on pavement, which he called secondary shadows (ombre derivative)—as well as the shadows that were projected in the air between these discrete objects and the walls or pavement forming the background.
Even a young artist in training would be able to follow his instructions. All he had to do was to imagine that a small circle, for instance, was a human head and then place the figure in similar lighting conditions. For instance, in one especially beautiful shadow drawing, two suspended spheres with nuanced penumbras generated by different light sources provide the optical basis of the heads from the Virgin of the Rocks.
In these diagrams, he would reveal the secret behind his signature blurring effect, which came to be known as Leonardo’s sfumato, although Leonardo never used the word.
This series of immensely complicated technical drawings on light and shadow was the centerpiece of the book. They were, in a sense, the core of his art as philosophy, for they revealed in a visual language that other artists could readily understand the immense power of the secret tool Leonardo had employed for many years in the service of a new type of painting. They taught artists to look at the surfaces of people—their skin, hair, and expressions, and even the smallest of motions—and to capture them with the slightest gradations of light, shadows, and penumbras, and with subtle colors or the smooth layering of glazes, to paint the purpose of their soul (i concetti dell’animo loro).
The section on light and shadow was where Leonardo’s stunning originality resided. This was also where Leonardo explored a revered concept from Aristotelian philosophy that no artist had ever applied to shadows or painting.
Aristotle used the concept of infinite divisibility to explain the physical world. It stated that space, time, and motion, which are continuous, can be divided into smaller parts, which can themselves be further divided, the process never terminating in something that is indivisible. Some philosophers, the atomists first among them, had harshly criticized infinite divisibility because they believed that there are small elements in nature that are indivisible—namely, what they called atoms. But for other philosophers, infinite divisibility allowed them to break down and so better understand complex natural phenomena.
In fact, some Arab philosophers had applied Aristotle’s principle of infinite divisibility to shadows. There are instances in Leonardo’s writings that seem to suggest he did read some detailed work on shadows and penumbras in his twenties in the library of San Marco, which may have inspired his own treatment of shadows based on Aristotle’s concept of infinite divisibility. But there is no way to know for sure or to identify what those hypothetical sources were.
He wrote, however, that “shadow partakes of the nature of universal matter,” and that like any other natural element, shadows can be divided endlessly into smaller units. As Aristotle had done with space, time, and motion, Leonardo divided objects and light sources into ever smaller units. What resulted was a web of lines that revealed how much light and how much shadow could be found in each spot in a drawing, which made it possible to show with geometric precision minute gradations in light and shade.
This was a clear instance of his originality, old ideas deployed to new ends.
In his optical diagrams, there are shadow rays (razzi ombrosi)—Leonardo had lifted the term from Ghiberti’s Commentaries—that combine in the air with light rays (razzi luminosi). It was as if Leonardo was portraying, with geometrical precision, solid bodies rather than thin air.
He imagined sunlight coming into a room through a large window or small aperture, and he imagined how it sifted through the clouds, the sky reflecting filtered sunlight all around. Alhacen had analyzed in detail similar lighting situations, and Leonardo had painted a few.
Leonardo believed the optical effects described in the notebook on light and shadow and in other folios made the art of painting superior to all the other arts, an argument he planned to expand in his art book, perhaps even in its opening section. In fact, he felt so strongly about the superiority of painting that he defended it forcefully in public debates at court.
In Renaissance courts, a favorite entertainment was the staging of debates on controversial topics—prominent courtiers were called to participate, each courtier defending opposing views, each resorting to subtle and witty arguments to amuse the ruler and his guests. Given his bright intellect, his wit, and his vast knowledge, Leonardo was the perfect courtier for such public debates. At least twice he argued for the supremacy of painting. One time, in 1498, in front of cardinals, generals, courtiers, and “eminent orators, experts in the noble arts of medicine and astrology,” he faced his friend Luca Pacioli, a Franciscan polymath and Sforza courtier, whose job was to defend mathematics, one of the liberal arts.
Since antiquity, debates on the paragone had excluded painting and sculpture because they were considered manual rather than intellectual arts. Only poetry, rhetoric, and music were arts of the mind. But this view began to change in the fifteenth century, when artists started to write their own art books. Cennino Cennini said that painting ought to be “crowned with poetry.” Leon Battista Alberti wrote that painting, like rhetoric, was meant to persuade viewers. Lorenzo Ghiberti argued forcefully that painting and sculpture were pursuits of the mind, not just of the hands. Ghiberti’s expertise in optics was an indication of his intellectual interests, his friendship with scholars the proof he was not merely a craftsman.
Leonardo was familiar with the writings of his fellow artists from earlier generations—Cennino, Alberti, Ghiberti—but unlike them, he argued his case based on what was said in optical literature, including in Alhacen, in favor of sight over other sensory organs. There lay the origin of his genius.
For Leonardo, painting was superior to all the arts because it dealt with “subtle speculations” that no other art was concerned with. Unlike other artists, painters engage in a “higher mental discourse [maggiore discorso mentale]” because their work is based on sight, which is the noblest sense and the closest to the common sense. Painting is superior to poetry because it creates its own images, while poetry uses words to recall actions, places, and forms (“form” is another term used by Alhacen, which Leonardo may have lifted from Ghiberti’s translation). It is also more universal than poetry because languages change from country to country, but the forms of painting are understood everywhere. And painting can represent different things simultaneously, while poetry can evoke them only one after another.
Music is the “younger sister” of painting, because music addresses the sense of hearing, which is inferior to sight, although music is superior to poetry because it creates sounds simultaneously.
Above all, painting is superior to sculpture. Unlike painters, sculptors cannot “depict transparent bodies.” They cannot “show the colors of all things and their diminution,” nor can they represent “luminous sources, nor reflected rays, nor shiny bodies such as mirrors and similar lustrous things, nor mists, nor dreary weather.” Nor they cannot render “veiled figures which show their nude skin under the veil that covers them; or small peddles of various colors underneath the surface of transparent water.” In sculptural works, “aerial perspective is absent.” This comparison between sculpture and painting was a constant in Verrocchio’s bottega, where the same design could be rendered in paint, marble, bronze, or terra-cotta. Leonardo himself often painted objects his master had made in metal or marble—we have only to remember Mary’s lectern in the Annunciation or the glass vase in the Madonna of the Carnation (Figures 2 and 3).
Around 1490, as a mature artist, Leonardo transcribed workshop conversations on painting and sculptures into a philosophical discourse based on the comparison of the senses that he had learned from optical literature.
Later in life, Leonardo would unabashedly say that the painter is “the lord and creator” of all sorts of people and “of all things man can think of,” but also “the monstrous things which might terrify.” But around 1490, he was content to state that painting was merely the “kin of god” and the “granddaughter of nature,” and that those who despise painting do not love either philosophy or nature.
He would be equally categorical, later in life, about who should read his notes as well. “Let no one who is not a mathematician read my principles,” he wrote next to a drawing of pulmonary valves that he may or may not have made with his art book in mind.
Leonardo worked consistently on his art book for a period of two or three years. He made concrete progress on themes that he planned to develop fully in the various sections of his book, or libri, as such sections were often called in the Renaissance. The folios about the skull located the common sense in the head, charted the way emotions travel through the body, and connected the skeleton to facial proportions. Other folios dealt with other parts of human anatomy, still others with the proportions of the entire body. Another notebook discussed colors and the atmosphere and offered a comparison of the arts. Another notebook dealt with the science behind penumbras.
Leonardo never came to a final decision about these various sections, not even about how many of them would be included.
But he did draft a table of contents of sorts: “On the Order of the Book.”
“This work should begin with the conception of man,” he wrote. It continued with the nature of the womb, then the anatomy of children and how their limbs grow, and proceeded to the anatomy of a grown male and female, showing their blood vessels, nerves, muscles, and bones.
The four “universal conditions of man” followed: he associated joy with various ways of laughing; weeping; combating with “various acts of killing, fight, fear, ferocity, boldness, murder”; and labor “with pulling, pushing, carrying, stopping, supporting and similar things.”
Then there was a section on attitudes and a final section on effects, which was devoted to “optics through the function of the eye; on hearing, I shall speak of music; and describe the other senses.”
The table of contents remained but a draft. He kept the different sections gathered in separate folio sets, each waiting to find its proper place within the overall structure.
Around the time he was drafting his art book, Leonardo also began to imagine an art academy, a school where—we presume—artists would learn about the science of art from his book. All we know about this academy is what we can glean from an engraving somebody made, presumably after a drawing by Leonardo.
A beautiful, intricate knot is tied around the words, in Latin, “Academia Leonardi Vinci.” According to the art historian and Leonardo scholar Pietro Marani, we have to think about Leonardo’s academy as “a group of artists who freely gathered around Leonardo, who learned from him not only the rudiments of art but also theoretical teachings from his own voice.” In fact, about seventy years later, a doctored selection of notes that Leonardo had written for his planned art book became the textbook for newly founded art academies in Florence and Paris, and possibly in Rome, too.
Later, Leonardo worked on his book on painting more and more sporadically. He sketched diagrams but did not provide accompanying texts. He stopped numbering his various folio sets, and soon he abandoned them altogether. On May 17, 1491, he started another notebook. That evening, sitting in candlelight at his desk, he wrote: “here a record shall be kept of everything related to the bronze horse, presently under execution.” The horse he was designing for the duke had consumed Leonardo’s attention, and the great book on the science of art was destined to be yet another of Leonardo’s unfinished projects.
But even though he abandoned these drafts, he did not entirely abandon the idea of a book. He spent the rest of his life revising the principles he had so carefully extracted from optical literature, including Alhacen’s work, while at the same time perfecting the technique of painting people’s souls.