Zaccolini and Leonardo's Manuscript A

by Janis C. Bell

Originally published in Il collezionismo dei leonardeschi a Milano e la Madonna Litta, Ed. M.T. Fiorio e P.C. Marani, Milan: Electa, 1991, pp. 183-93.

The Documentary Evidence

Internal Evidence in Zaccolini's Manuscripts

Zaccolini's Knowledge of MS A.

Matteo Zaccolini was a Theatine perspective painter and the author of a four volume perspective treatise. Seventeenth century writers claimed he was the teacher of Domenichino, Filippo Gagliardi, and a consultant to Pomarancio and the Cavalier d'Arpino for problems in perspective painting. The Frenchmen, Félibien, lauded his accomplishments in perspective painting, and noted that he was greatly esteemed by Poussin. Dughet wrote that he made a copy of the treatises for Poussin, and Félibien wrote that Poussin "showed what he had learned from Zaccolini in his paintings."note 1 His treatises were greatly admired by Cassiano dal Pozzo, who prepared his own copy of them during the 1630's while at work on preparing the edition of Leonardo's Trattato della Pittura which was eventually published by Raphael Du Fresne.note 2

Nevertheless, Zaccolini was forgotten in subsequent generations. His paintings were destroyed with the sequestration of the Theatines and his manuscript treatises were lost in the large uncatalogued collections of the Barberini and others. He would have remained nothing but a footnote to history were it not for Carlo Pedretti's success in locating the manuscripts nearly twenty years ago in the Ashburnham collection of the Biblioteca Laurenziana in Florence.note 3 His interest had been stimulated by a short biography of Zaccolini written by Dal Pozzo, bound into a manuscript of miscellaneous notes and transcriptions relating to the edition of Leonardo's Treatise on Painting.note 4 The discovery of the manuscripts makes it possible to confirm the allegations of Dal Pozzo and other sources that Zaccolini knew and admired the writings of Leonardo da Vinci--not just the Treatise on Painting which was circulating in numerous manuscript copies, but also at least some of the original notebooks. The purpose of this short paper is to provide evidence that Zaccolini knew at least one of those notebooks.

The Documentary Evidence

Let me first review the documentary evidence. Our best witness is Cassiano dal Pozzo. In his Montpellier biography, Dal Pozzo wrote that, in his treatise, Zaccolini

explained many things pertaining to Leonardo's Treatise entitled Opinion of Leonardo da Vinci about the way of Painting Perspectives, Shadows, Distances, High and Lower Places from nearby and far away, and so on. On account of which treatise, and because he had seen many things written by Leonardo in mirror script, the said Matteo got used to that kind of writing and began writing many of his notes in that manner with great facility and in well-formed script, so that no one could at first understand them.note 5

Cassiano is here attesting to Zaccolini's knowledge of a manuscript copy of the Treatise on Painting--what he calls "Opinion of Leonardo da Vinci...,"--as well as to Zaccolini's knowledge of manuscripts in Leonardo's own hand. Indeed, he indicates that Matteo became so familiar with Leonardo's idiosyncratic handwriting that he began to imitate it.

Perhaps we could dismiss this as a curious rhetorical exaggeration, if we did not know as much as we do about Cassiano dal Pozzo.note 6 He was a careful scholar and serious antiquarian. His letters and papers on the Leonardo project and other publications that he administered reveal a concern for accuracy comparable to the best scholarship of his age. There is no reason to doubt his assertion that this biography of Zaccolini was based upon an autobiographical account by the artist/writer, for Cassiano lived in Rome in the palazzo adjacent to the Theatine house of Sant'Andrea della Valle.

Zaccolini also spent most of his life in Rome. He arrived from Cesena in late 1599, professed as a Theatine lay brother at San Silvestro a Monte Cavallo (now known as San Silvestro al Quirinale), and died at San Silvestro in July of 1630. In the spring of 1623, Zaccolini spent three months living at Sant'Andrea della Valle, after having returned from a temporary period of residence in Naples. It is likely, therefore, that Cassiano had the opportunity to acquaint himself personally with the Theatine artist and writer.

The author of the manuscript Nota delli Musei, Librerie, Gallerie & Ornamenti di Statue, e pitture, ne Palazzi, nelle case, e ne Giardini di Roma of 1664, which has been convincingly attributed to Bellori, described various treatises by Zaccolini in the library at San Silvestro "in his hand written backwards, as Leonardo da Vinci used to do."note 7 Although the accuracy of this reference has been questioned--and there is no doubt that the author was relying upon hearsay and did not personally check out all of his assertions--it is still a valuable piece of evidence for Zaccolini's reputation as a student of Leonardo da Vinci.note 8

Furthermore, Baglione, writing before 1642, also commented on Zaccolini's familiarity with Leonardo. In a short biography of less than one page, he noted that Zaccolini had studied "in particular the writings of Leonardo da Vinci."note 9 Thus, we know that Zaccolini had a reputation in early Seicento Rome as a modern commentator on Leonardo and as a curious imitator of Leonardo's idiosyncratic writing.

Internal Evidence in the Zaccolini Manuscripts

There is also much internal evidence, that is, evidence in the manuscripts themselves, that Zaccolini had studied the writings of Leonardo. No doubt he knew the Treatise on Painting well. Numerous copies of it were available in Seicento Rome, in the collections of artists, art academies, and wealthy book collectors. The contents of the second volume of his treatise, Prospettiva del Colore, deal with many topics that engaged the attention of Leonardo, but had been largely ignored by subsequent Cinquecento writers, such as the relationship between background color and relief, aerial perspective, and light and shadow. I am currently preparing an edition of this volume.note 10

The manuscripts themselves, however, are copies made in the workshop of Cassiano dal Pozzo, as I have shown elsewhere,--not writings "in rovescio" in the manner of Leonardo da Vinci.note 11 Yet they can still help us to corroborate the assertions of later biographers about Zaccolini's familiarity with Leonardo's original notebooks. For one thing, Zaccolini himself alluded to a knowledge of writings that "could only be read by looking at the image of the characters in a mirror or in water."note 12 I believe this can be taken as a reference to Leonardo although he did not mention Leonardo by name.

However, several difficulties stand in the way of establishing Zaccolini's familiarity with any particular Leonardo manuscript. For one thing, a great many of Leonardo's ideas were not totally original, and since Zaccolini read many of the same classical and medieval scientific texts that Leonardo had consulted, the identification of similar ideas does not necessarily indicate a borrowing. Furthermore, Zaccolini rarely paraphrased his sources. He read Leonardo and other texts critically, rephrasing ideas in his own words, elaborating and expanding upon both commonplaces and unusual ideas in light of his own experiences as a practicing artist.

Barring these difficulties, I believe it is possible to demonstrate that Zaccolini was indeed familiar with at least one original notebook of Leonardo da Vinci. This notebook is Paris MS. A. In the last section of Zaccolini's second volume, Prospettiva del Colore, are five chapters grouped together as "Trattato 17" and four of them are closely related to passages in MS. A. However, since many passages from MS. A were transcribed by Melzi into the Treatise on Painting, we have to fine-tune our method as follows: in order to demonstrate that an idea came from a Leonardo notebook, we have to be able to show either that it derives from a passage that was not transcribed into the Treatise on Painting, or that this passage was not copied into the abbreviated redaction of the Treatise on Painting, that is, the short version circulating in manuscript copies during the sixteenth and seventeenth centuries.note 13 (The manuscript of the Treatise on Painting which is today in the Vatican Library (Codex Urbinas Latinas 1270), was in the Ducal collection in Urbino during Zaccolini's lifetime and its whereabouts were not known to Zaccolini nor to other Leonardo collectors in Rome and Naples.)note 14 Furthermore, some aspect of the idea paraphrased ought to be peculiar to Leonardo so as not to have been found in the basic scientific literature studied by Zaccolini. The passages from MS A meet these tests, as only two of them appeared in the abbreviated redaction of the Treatise on Painting.note 15

The first chapter of Zaccolini's Trattato 17 (17.1) is entitled "Standing in a street and looking towards the darkness inside the doors and windows, you can't see the objects that are in there." It follows a passage from MS. A 90a (BNF Ash. 2038, fol. 10a) which is entitled "All colors are at a distance undistinguishable and undiscernible"(Ri 293). Although this passage had been transcribed into the Codex Urbinas, fol. 205r-v (Mc 815, Lu 799), it had not been copied into the abbreviated redaction.note 16 Leonardo described a person looking towards a house from outside, unable to see anything but darkness through the doors and windows even though the level of illumination was sufficient for a person looking around inside the house. He used this situation to illustrate the principle that an object cannot transmit its image to the eye through an atmosphere more luminous than the object itself.

All colors at a distance are undistinguishable in shadow, because an object which is not in the highest light is incapable of transmitting its image to the eye through an atmosphere more luminous than itself, since the lesser brightness must be absorbed by the greater. For instance: We, in a house, can see that all the colors on the surface of the walls are clearly and instantly visible when the windows of the house are open; but if we were to go out of the house and look in the windows from a little distance to see the paintings on those walls, instead of the paintings we should see a uniform deep and colorless shadows.note 17

Zaccolini used the same example of objects that are seen in full color and detail when the viewer is inside the house, but look obscure when viewed from outside. However, in contrast to Leonardo, he argued that the image of these objects were transmitted to the eye, but the visual sense was unable to register the sensation because the bright light was excessive enough to interfere with vision.

Whenever strong light makes a strong effect on vision, it prevails by preventing the species of color from perfectly impressing their images inside the eye to move the visual sense. The reason is that this impression [of the speties] requires blackness, yet because the eye is illuminated by excessive light, it would seem, that the sense would have already been moved by the same dark place of a black tint around the crystalline humors. This part of the eye being strongly illuminated, it acts as if it itself sees; what really happens is that the sense, moved from this black tint, sees only the darkness and is not able to see the images of the other objects. Thus, it acts as if it has been trampled upon or extinguished.

(Book 17, chapter 1, fols. 147v-148):

Quando il lume sarà molto gagliardo facendo movimento alla vista, prevale in tal maniera che le spetie dei colori non possono così perfettamente imprimere le imagini dentro all'occhio per muover il senso, essendo che tale impressione si fanno nel nero, perciò essendo l'occhio da soverchia luce illuminato, pare che il senso sia mosso dall'istessa oscurità posta di tintura negra intorno à gl'humori christallini perciò illuminandosi soverchiamente questa parte dell'occhio vedendo se stesso, mosso /[148] il senso da tale tintura negra vedendo l'oscurità non potendo vedere l'imagine degl'altri obbietti restando come conculcate et estin

This explanation builds upon archaic notions of the crystalline humors and black tints inside the eye--concepts typical of the theory of vision before Platter, Kepler and Descartes but making little sense to the modern reader. Rephrasing these ideas, we can reduce Zaccolini's explanation to the following: the light sensitivity of the eye has a certain maximum threshold (e.g. the quantity of sensitive blackness surrounding the crystalline humor); the bright light from outside reaches this threshold, making the eye insensitive to the lesser light from indoors because it is not strong enough to compete for the same sensitive blackness that is already in use; thus the viewer perceives darkness and obscurity.

Zaccolini went on to mention the role of the pupil in admitting light to the eye. When too large, it would admit too much light, creating visual problems such as myopia.note 18 Leonardo had also explored the role of the pupil, coming up with several original speculations.note 19 Among these was the idea that the pupil contracts or dilates according to the amount of incident light--an idea based upon the Aristotelian premise that nature maintains itself in a dynamic state of equilibrium, continually adjusting the light sensitive mechanism of the eye.note 20 Although this idea was anticipated by the tenth century Arab writer, al-Razi, the role of the pupil had been virtually ignored by optical writers in Greek antiquity and medieval Islam and Christendom.note 21 Another original idea was that the size of the pupil affects the size of the image, a larger pupil leading to a larger image.note 22 Zaccolini's failure to refer to these ideas in the context of a discussion of pupil function and excessive light indicates that he did not know MS D, nor was he likely to have known other manuscripts dealing with the function of the eye, such as I, L, and H.note 23 Instead, Zaccolini's reference to the short-sighted eye leads me to believe that he had consulted a medical source which I have not yet been able to identify.

The next chapter in Trattato 17, "How to determine where the highlights will be on a shiny surface that acts like a mirror" (17.2) is more appropriately included in a section headed "On Pictures that Shine (Delle Pitture che Lustrano)."note 24 The concept is closely related to a passage in MS. A 32 (BNF Ash. 2038, fol. 32), which had been copied into the Codex Urbinas but was not found in the abbreviated redaction in circulation in the sixteenth and seventeenth centuries.note 25 Both writers used illustrations to clarify their arguments, Leonardo using a line diagram, Zaccolini a grisaille illustration on a small sheet glued onto the page at the left margin, slightly overlapping the text. The scribe had left room for the illustration, which turned out to be wider and lower than the space allotted. (Figures 1, 2, 3). Zaccolini's chapter is not a paraphrase. Leonardo deals with round objects, revealing his debt to the medieval science of catoptrics (reflections in mirrors) in which the location of images in spherical mirrors was a frequent concern.note 26 Zaccolini presents the case of a plane figure, the equivalent of a lustrous painting. The general principle, however, is the same: the luster appears at the point of intersection of the cathetus (the perpendicular from the image) and the ray, such that the angle of incidence is equal to the angle of reflection.

This principle was commonplace in optics, with its roots going back to the study of catoptrics in Greek antiquity--and both writers were familiar with much of the scientific literature in this area. However, examining the commonly-used optical texts reveals that the problem was phrased in a very different way. Therefore, I think we can make a case for Zaccolini's familiarity with Leonardo for two reasons. Both authors are concerned with the accuracy of the painter's rendition of surface lusters, that is, the points of reflection on shiny surfaces. Second, both authors emphasize the principle that the luster appears to move as the observer moves.

Leonardo's text reads as follows:

Of the highest lights which turn and move as the eye moves which sees the object. Suppose the body to be the round object figured here and let the light be at the point a, and let the illuminated side of the object be b c and the eye at the point d: I say that, as luster is everywhere and complete in each part, if you stand at the point d the luster will appear at c, and in proportion as the eye moves from d to a, the luster will move from c to n.note 27

Zaccolini defined the luster as "the image or reflection of the light source." After explaining that this reflection rebounds to the eye at the same angle with which the light percusses (that is, hits) the illuminated surface, he argued that finding the location of the lusters is a necessary task for the painter wishing to imitate nature. He then presented a diagram to illustrate the method to use in locating the lusters. Condensing Zaccolini's rather wordy text, we can follow the diagram in which the line AB is perpendicular to the ground and on which is raised the illuminated [picture] surface. Point C is the luminous source placed in front of it. When the eye is at point K, the point of luster will be at point F on the surface AB, but will seem to be beyond the surface by as much as the light is distant from the surface AB, hence at the distance D. In order to determine where to place this point of reflection, the artist should first draw a line at right angles to AB coming from C, and continuing beyond the same distance to D. Then a line should be drawn from D to the position of the eye at K. The point of intersection with the surface, F, is where the luster should be represented.

Zaccolini observed that although the light source and object remain stationary, the luster will appear to move as the eye

It is this very luster and image that will appear on the same perpendicular plane (like Leonardo, he uses the word parete)note 28 now in one place and now in another according to the diverse sites where the eye is placed. Nevertheless, as the sites vary, whether from nearby or from far away, from above or from below, these lusters or images will continually vary. You can call them whatever you wish because one and the other are essentially the same. Luster does not differ from the image other than that sometimes they doesn't show the image in all its perfection. And since the luminous body does not move its site, but it is the eye that moves, it will seem that the image is moving and changing its site on the surface.

(Book 17, chapter 2, fol. 149v)

quello tal lustro e imagine apparerà nell'istessa parete hora in un luogo et hora in altro secondo che con l'occhio si starà collocato in diversi siti tuttavia si variarannò di sito poiche se da vicino e da lontano, et hor alto, et hor basso con l'occhio di continuo si variarannò questi lustri o imagine, chiamandosi in qual maniera si vogliono perche l'istesso l'uno che l'altro, benche il lustro non differisca in altro dall'imagine se non che alle volte non dimostrano l'imagine di tutta perfettione e benche il luminoso corpo non si muova di sito, movendosi l'occhio, parerà che si muova l'imagine, mutandosi di sito nella superficia

Returning to the diagram, we see that Zaccolini, like Leonardo, includes a second situation: if the eye is moved lower to point M, the luster will now appear in G. However, if the eye is moved anywhere along the straight line between the eye and D, either closer or further from the surface, the luster will appear at the same point. Thus, when the eye is at N or at P, the luster will still appear at F or G respectively.

Zaccolini's argument that the luster appears behind the surface is also found in Leonardo's writings in another passage from MS A on folio 19v (where Leonardo also talks about the movement of the image with the movement of the eye). Leonardo wrote "if the object c is in n it appears as much behind as it is away [from the mirror]; therefore c appears to be at d./ se la cosa c e in n ella pare di tanto dentro quanto ella e fori; adunque c si vedera in d."note 29 (Figure 4) Since this idea was commonplace in the science of catoptrics, it alone would not be sufficient to establish Zaccolini's knowledge of Leonardo. I bring it in, however, because in the context of these other ideas on lusters, additional parallels can reinforce the thesis.note 30

Zaccolini's next chapter 17.3, is entitled "Where the eye should be for the most comfortable viewing of pictures that shine." It further develops these ideas on the location of lusters, and relates closely to MS A 113v (BNF Ash. 2038 32b) entitled "Where a spectator should stand to look at a picture" (Ri 547; CU 134, Mc 555, Lu 415). Leonardo presents a line diagram (Figure 5), and explains that line ab represents the picture while point d represents the light source, which is a window. Since point c will be the maximum lustre, the spectator is advised to stand between d and e (the shaded area on the diagram) to avoid the interference of reflections.

Supposing a b to be the picture and d to be the light, I say that if you place yourself between c and e you will not understand the picture well and particularly if it is done in oils, or still more if it is varnished, because it will be lustrous and somewhat of the nature of a mirror. And for this reason the nearer you go towards the point c, the less you will see, because the rays of light falling from the window on the picture are reflected to that point. But if you place yourself between e and d you will get a good view of it, and the more so as you approach the point d, because that spot is least exposed to these reflected rays of light.note 31

Zaccolini's diagram (Figure 6) duplicates Leonardo's except that it has been expanded to illustrate two possible situations. The line AB represents the picture surface, D is the light source, and the angle DF the optimal viewing position to avoid the reflection at point G. The second situation is superimposed. The light source, D, is constant, but HS represents the picture plane; now the optimal viewing position would be within the angle FG to avoid the reflection at point D (due to the perpendicular placement of the light).

Zaccolini's discussion is also dependent upon Leonardo, for this particular issue was not discussed in the optical literature, nor was it to be found in Cinquecento art treatises.note 32 Indeed, Zaccolini's text reads as a wordy paraphrase of Leonardo, for like his source, he oriented the discussion towards paintings in oil or those that are varnished such that they shine and act like mirrors. Furthermore, his light source is a window rather than a candle or torch. The fact that this passage was retained in the abbreviated redaction of the Treatise on Painting accounts for the close similarity.

Another illustration for this chapter, found loose by Pedretti and now attached to a sheet at the end, shows the ideal viewing situation in a perspective drawing.(Figure 7) In the upper drawing, the painting surface AB is set at an oblique angle to the light source, with the ideal viewing position at F, because the luster will be seen at G. Below, the painting HS is turned perpendicular to the direction of the light, and the optimal viewing position is now between F and G. The presence of this illusionistic grisaille drawing following a line diagram is characteristic of Zaccolini's manner of presentation, where it is used extensively in the volume on cast shadows.note 33 I suspect, however, that this may be the invention of the illustrator employed in Cassiano dal Pozzo's workshop, for there is no reference to it in the text.

In the following chapter, 17.4, Zaccolini basically plagiarized Leonardo's drawing as it appeared in the Treatise on Painting (Figures 8 and 9), but transformed the context to demonstrate how the painter ought to adjust the lighting in a chapel or other viewing location in order to avoid disturbing lusters on the painting. His text explains that AB represents the picture placed directly opposite the eye in F. If the light source comes from this same direction, the viewer will see nothing but the luster; therefore the painter is advised to close up this window and put in one which will permit lateral lighting.

The best remedy for this inconvenience would be to build, closing up the window in part F and opening another one to the side, or even on the same wall but placed opposite [the painting] in such a way that the light which illuminates the picture is oblique. For example, if the window where the light enters is in D, as it illuminates the painting it will reflect elsewhere in G at an equal angle. Thus, at this point G the luster of the image of the light will be seen, and at the part F where the eye rests, not being able to see the lusters of the image, the beholder will comfortably see the picture without any offence to the visual sense.

(Book 17, chapter 4, fol. 153)

...per il cui inconveniente ottimo rimedio sarà fabricare e chiudere la finestra della parte F. e farne un'altra laterale o veramente nell'istessa facciata posta in tal guisa dirimpetto che il lume vada ad illuminare la Pittura obliquamente, come che la finestra per dove doverà entrare il lume fusse in D. illuminando il quadro si rifletta- ra nell'altra parte in G in angolo uguale percio da questa G si vedrà il lustro dell'imagine del lume o la parte F dove starà posto l'occhio non si potendo vedere i lustri dell'Imagine si potrà vedere commodamente la pittura senza alcuna offesa del senso visibile?

With this lateral lighting, the light coming from D will have its luster in G, and therefore the viewer will see the picture without difficulties at F.

The opposite situation is also addressed--that is, where the light is oblique and the viewer is also oblique, such that the painter would need to block off the light at G and put in a window at D. A grisaille illustration (Figure 1), also now attached at the end because the copyist failed to leave a space for it, shows this situation with a picture in a church. The identifying letters on the drawing are somewhat obscured by the darkening of the ink, but one can still ascertain that C is the archway in the distance by which one views the picture wall AB at an oblique angle, F is the window directly opposite, D is the high window, and G is the low window, all on the wall facing the picture.

The last chapter in Trattato 17 entitled "You can only see exactly by looking at one point at a time" also recalls ideas in a passage from MS A that was retained in the abbreviated redaction of the Treatise on Painting. Leonardo's passage on folio 108a is entitled "What rules should be given to boys learning to paint." (BNF Ash. 2038, folio 28a, Ri 491: CU 31a-b, Mc 60, Lu 49) In the first part of this passage, Leonardo makes an analogy between the step by step study of painting and the process of visual comprehension, alluding to the difference between glancing and careful looking.

We know for certain that sight is one of the most rapid actions we can perform. In an instant we see an infinite number of forms, still we only take in thoroughly one object at a time. Supposing that you, Reader, were to glance rapidly at the whole of this written page, you would instantly perceive that it was covered with various letters; but you could not, in the time, recognize what the letters were, nor what they were meant to tell. Hence you would need to see them word by word, line by line to be able to understand the letters....note 34l

Leonardo then goes on to give other examples of operations that need to be performed step by step, in order to create a foundation for the argument that the young painter must proceed systematically, mastering elementary things before undertaking more complex tasks.

Thus I say to you whose nature turns towards this art: if you want to have true knowledge of the forms of things, begin with the details of them and do not go to the second step if you do not have the first mastered in practice and in memory. If you do otherwise, you will waste time and even prolong your studies. And remember to learn diligence before facility.note 35

The title of Zaccolini's chapter--that you can only see at one point at a time--indicates a different focus. However, he makes use of the same analogies to argue his point, suggesting a dependence on Leonardo in the context of the other passages. Just as Leonardo had referred to the process of visual perception as a model for the painter to proceed systematically, Zaccolini similarly argued that a mere glance is insufficient to memorize the distinctive features of a person so that they can be recorded in a portrait. The painter must proceed step by step, studying and observing the face in order to comprehend each of its minute parts.

However, in this the painter has a great deal of experience for in making a portrait of someone it is not enough to have seen him the first time all at once. Rather, it is necessary that the image should continually present itself to the mind following along with the sense of vision as it exactly looks at and observes all the most minute parts down to the smallest point. This careful observation will give finish and perfection to a painted portrait.

(Book 17, chapter 5, fol. 154):

"Perciò di questo ne suol fare esperienza i Pittori, i quali nel fare il Ritratto di alcuno non gli basta quella prima vista di vederlo tutto ad un tratto mà e necessariò che del continuo presenti al mente vada con la vista esattamente risguardando, e osservando tutti le parte piu minute sin un minimo punto per dare compimento e perfettione al ritratto fatto di Pittura

The analogy to reading is then invoked to reinforce the benefit and necessity of a gradual, cumulative process.

This principle can be proved more conclusively to anyone who wants to look at an open book or some other obvious thing where all the letters that are on this sheet would be seen at once, that is, with a simple glance. Nevertheless, if asked what letters they are, the reader certainly will not be able to identify them accurately. In order to know them it will be necessary to fix the glance on one at a time, looking at them as if reading them.

(Book 17, chapter 5, fol. 154):

...e non ostanti questa ragione lo proverà più evidentemente ognuno sia chi voglia risguardando un libro aperto o cosa manifesta che vedra ad un tratto con una semplice occhiata tutte le lettere che in quella carta sarannò non dimeno si dimanda se egli saprà che [154 v] lettere siano quelle certamente non si potrà dire con verità quali siano, mà per saperlo sarà necessario che à una per una affisando lo sguardo li vada tuttavia vedendo nel leggerle, non essendo possibile per veloci che sia lo sguardo di poterne vedere più che una per v

The notion that sight operates in two ways was commonplace in optics. Its roots go back to the eleventh century Arab writer, Ibn al-Haytham, known in the West as Alhazen. In his long treatise on optics, Ibn al-Haytham had distinguished between vision by glancing and vision by contemplation.note 36 Vision by glancing would take in all of the rays of light emanating from the object contained within an imaginary cone which had its apex in the center of the eye. However, only the part of the object in the center, directly opposite the eye would be perceived clearly and distinctly. All of the other parts would be vague, since the rays were not perpendicular to the surface of the eye and would therefore be refracted as they passed through the watery humors inside the eye.note 37 This process was adequate for the recognition of familiar things, but in order to comprehend precise details, or to build recognition of new things, the eye would have to operate by contemplation, scrutinizing each part of the object by moving the eye in order to align that part with the center of the sensible organ.note 38

Zaccolini most probably knew Ibn al-Haytham's treatise, which had been published in Latin translation in 1572 by Friederich Risner together with the Ten Books on Optics of Witelo.note 39 The explanation that follows the passage quoted above summarizes Ibn al-Haytham's theory of distinct vision by means of the perpendicular ray. (Leonardo, incidentally, may also have been familiar with the Italian translation of Alhazen known to Ghiberti, now in the Vatican Library.)note 40 However, the theory of distinct vision by means of the perpendicular ray was so diffused in Renaissance philosophy that it is impossible to pinpoint Zaccolini's source.note 41

His debt to Leonardo, however, is more certain, for only these two authors use the specific example of reading letters on the page of a book to convince painters that they must continually examine and observe their subjects in order to give perfection to the representation of nature.note 42

It is significant that chapters 17.3 and 17.5 which both derive from passages included in the abbreviated version of the Treatise were paraphrased more closely than the two chapters 17.1 and 17.2 based upon passages accessible only in the original notebooks. This suggests to me that Zaccolini had a copy of the Treatise available to him when he was writing in Rome and Naples, but had to rely on his notes and recollections for material from the original manuscripts.note 43

Zaccolini's knowledge of MS A

How Zaccolini got the opportunity to read MS. A is still a mystery. This volume was part of the Arconati donation to the Ambrosiana in 1636, and presumably was one of the 15 small notebooks in the Leoni collection which were offered for sale to Duke Cosimo II of Florence in 1614.note 44 But we cannot assume that Arconati owned the treatises much before 1622, when he paid 45 ducatoni towards a debt of 445 ducatoni to Francesco Maria Calcho, Leoni's grandson. Were the notebooks in Milan during these 8 years, requiring us to postulate a trip to Milan by Zaccolini or were some of the manuscripts brought to Rome or to Naples?

Let us consider the first possibility. Zaccolini stated in the Letter to the Reader in De Colori that he had lived in "various other countries," not only in Rome but wherever his superiors sent him.note 45 Perhaps he spent time in the Theatine center of S. Antonio Abate in Milan or in one of the outlying areas. The Theatine order was growing rapidly in the early seventeenth century and had opened several houses in Lombardy. Since the order had an efficient, centralized government, it was not unusual for lay brothers with useful skills to be transferred for short periods to places where their services were needed. Zaccolini's temporary transfer to Naples is an example; he helped there with the decoration of the residence at SS. Apostoli, with the design of the tabernacle there, and worked on stuccoes, fountains, and diverse ornaments at other Theatine churches in the area.note 46 Thus, a thorough study of the Theatine archives in the Milanese area may substantiate this hypothesis of a trip North.

The other possibility--that MS. A was in Rome or Naples--is somewhat less likely. We would have to assume that the Leoni family brought it there in order to sell it, or that Arconati (if indeed he purchased the manuscript before 1622 as Pedretti has suggested) brought it with him on a visit to the papal city. We know that Arconati visited Rome occasionally to purchase ancient sculpture for his villa at Castellazzo.note 47 However, the absence of notices of Leonardo notebooks (except for the Codex Leicester) in Rome or Naples casts serious doubts on this hypothesis. We will have to await the discovery on new documentation to resolve the mystery of where and how Zaccolini became so immersed in a study of Leonardo's notebooks that he undertook to imitate his peculiar practice of writing backwards.


1.  All the information on the life of Zaccolini and the vicissitudes of his manuscripts is extracted from my two earlier articles, "The Life and Works of Matteo Zaccolini (1574-1630)," Regnum Dei 16, 1985, 227-258; and "Cassiano dal Pozzo's Copy of the Zaccolini Manuscripts," Journal of the Warburg and Courtauld Institutes 51, 1988, 103-125.

2.  On the history of the publication of the Trattato della pittura, and for a list of all the manuscripts associated with this project, see Kate Steinitz, Leonardo da Vinci's Trattato della Pittura, Copenhagen 1958, and her two updates: "Bibliography never ends," Raccolta Vinciana, XVIII, 1960, 97-111, and "Trattato Studies. II," Raccolta Vinciana XVIX, 1962, 223-254.

3.  Carlo Pedretti, "The Zaccolini Manuscripts," Bibliothèque d'Humanisme et Renaissance XXXV, 1972, 39-53.

4.  Montpellier MS H 267. Cassiano's biography of Zaccolini has been transcribed and translated into English in Carlo Pedretti, Commentary to the Literary Works of Leonardo da Vinci, (Kress Foundation Studies in the History of European Art), 2 vols., Berkeley: U of CA Press, 1977.

5.  "nella quale ha spiegato moltisse.e cose che appartengono al Trattato di Lionardo da Vinci inscritto opinione di Lionardo da Vinci, circa il modo di dipigner Prospettiue, ombre, lontananze, altezze, bassezze da presso e da discosto et altro. Del qual Trattato di Lionardo come haueua uisto molte cose da quello scritto con carattere alla rouescia, così il detto Matteo s'assuefece à quella ragione di scrivere, e molte delle sue fatiche, acciò non fussero alla p.a intense da ognuno le haueua con facilità grande e con carattere assai aggiustato prese a scriuere in quella maniera." (Quoted from Pedretti, Commentary, I, 38-9.)

6.  The most important sources of information are Carlo Dati, Orazione delle Lodi del Commendatore dal Pozzo, Florence 1664, and Giovanni Lumbroso, "Notizie sulla vita di Cassiano dal Pozzo," Reale Deputazione di Storia Patria, Torino, Miscellanea, XV, 1876, 30-45, (also published as a separate volume in Turin: G.B. Paravia, 1875). In addition to the modern literature cited in Bell, 1988, see Francesco Solinas, Ed., Cassiano dal Pozzo: Atti del seminario internazionale di studi, (conference of 18-19 December 1987 in Naples) Rome: De Luca, 1989.

7.  Ed. Emma Zocca, Rome 1976, 51: "Et alcuni trattati del celebre Matematico, et Prospetico pittore il P. P. Matteo Zoccollini, l'un della prospettiva lineale l'altro de' colori con li disegni, et altri scritti à rovescio, come usava Leonardo da Vinci." Bellori's reference is perplexing, not only because he seems to refer to only one book on linear perspective and one book on color 'with illustrations', but also because he mentions 'commentaries on Euclid and the Sphere of Sacrobosco', for which we have no other documentation.

8.  On the authorship of the Nota, its date and its accuracy, see Giovanni Mercati, Ed., Nota per la storia di alcune biblioteche romane nei secole XVI-XIX, Studi e testi 164, Vatican City: Biblioteca Apostolica Vaticana, 1952, 151-3.

9.  Giovanni Baglione, Le Vite de' Pittori, Scultori, Architetti ed Intagliatori, (Rome 1642), Naples 1733, 204.

10.  To be published by Cambridge University Press.

11.  Bell, 1988, as in n. 1 above.

12.  Laur. Ash. 12121, 5v: "...alcune lettere scritte delle quali non si possono legger se non per refratione, risguardando alle imagine dei caratteri dentro alli specchi, o per l'acqua,..."

13.  On the abbreviated version of the Treatise on Painting, see Pedretti, Commentary, I, 12-36.

14.  Zygmunt Wazbinski suggested to me orally that Guidobaldo dal Monte in Pesaro knew this volume, and that it is therefore probable that it was also known to his brother, the Cardinal del Monte, in Rome.

15.  For a list of the chapters in Vat. Cod. Urb. Lat. 1270 omitted from the abbreviated redaction, see Carlo Pedretti, Leonardo da Vinci on painting; a lost book (Libro A) reassembled from the Codex Vaticanus Urbinas 1270 and from the Codex Leicester, Berkeley: U of CA Press, 1964, 241-51.

16.  To facilitate consultation of passages in Leonardo's oeuvre, reference numbers are given to standard editions with the following abbreviations: Mc = Philip MacMahon, The Treatise on Painting, (English trans.) Princeton: Princeton UP, 1956; Lu = H. Ludwig, Il Trattato della Pittura, (German edition with facing Italian), Vienna, 1882; Ri = J.P. Richter, The Literary Works of Leonardo da Vinci, London, 1883. Anyone consulting Richter should also consult Pedretti's Commentary for dating of the passages and other related information.

Another passage on the same subject is entitled "On the eye that is in a bright light and looks toward a darker place" (Mc 818, Lu 786) dated 1508-10 by Pedretti, Libro A, as in note 15, 176.

17.  TUTTI I COLORI NELLE LONTANE OBRE SONO IGNIORATI E INDISCERNIBILI/ Tutti i colori in lontano fieno nell'obre igniorati; perche la cosa; che non e tocca dal principale lume' non e potete a mandare di se all'occhio per l'aria piv luminosa la sua similitudine, perche il minore lume e vinto dal maggiore; Esenplo: Noi vediamo essendo in una casa che tutti i colori i quali sono nelle parieti delle mvra si veggono chiaro e speditamete, quado le finestre di detta abitatione fieno aperte; e se noi usciremo fori d'essa casa e riguardaremo un poco di lontano per dette finestre di rivedere le pitture fatte su dette mura in iscambio d'esse picture vedremo una cotinvata oscurita.

18.  Laur. Ash. 12122, fol. 148v: "Acciò questo cosi nobil et artificioso instrumento del vedere potesse essercitarsi nell'impressioni dell'Imagini per muover il senso acciò da soverchia luce non fusse impedito e molestato gli fece la piccolissima pupilla per l'ingresso della Luce e delle spetie, perciò quelli che hanno ampla pupilla sogliono essere di curta vista per la quale entrando soverchia luce l'imagini s'imprimono debilmente nell'oscurità, vedendo forsi se stesso..."

19.  Donald Strong, Leonardo on the Eye: an English Translation and Critical Commentary of MS. D in the Bibliothèque Nationale, Paris, with Studies on Leonardo's Methodology and Theories on Optics, New York: Garland, 1979. Kenneth Keele, "Leonardo's Physiology of the Senses," in Leonardo's Legacy: an International Symposium, Ed. by C. D. O'Malley, Berkeley and Los Angeles: University of California Press, 1969, 35-56.

20.  Strong, 332.

21.  David C. Lindberg, Theories of Vision from Al-Kindi to Kepler, Chicago: U. of Chicago Press, 1976, 163-4.

22.  Strong, 160-1, and 331.

23.  Strong, 329 and 331.

24.  This heading appears only in the index at the end, fol. 159v, for which reason it appears likely to have been the result of Cassiano dal Pozzo's editing.

25.  CU 220, Mc 779, Lu 746; Ri 133.

26. See John Pecham, Perspectiva communis, Book 2 (Ed. by David Lindberg, John Pecham and the Science of Optics, Madison: University of Wisconsin Press, 1970. Pecham was, of course, indebted to the De speculis by pseudo-Euclid, which was believed to be authentic in the middle ages. See Axel Björnbo, and S. Vogl, "Alkindi, Tideus und Pseudo-Euclid. Drei optische Werke," Abhandlung zur Geschichte der Mathematischen Wissenschaften, 26, 3, 1912, 1-176; and Paul Ver Eecke, Euclid: L'Optique e la catoptrique, Paris, 1959.

27.  DE'COLMI DE LUMI CHE SI VOLTANO E TRASMUTANO SECONDO CHE SI TRASMUTA L'OCHIO VEDITORE D'ESSO CORPO. Poniamo che 'l corpo detto sia questo todo qui d'acato figurato, e che il lume sia il puto a e che la parte del corpo alluminata sia b c, e che l'ochio sia nel puto d: dico che 'l lustro perche e tutto per tutto e tutto nella parte che stado nel puto d, che il lustro parra nel puto c e tato quato l'ochio si trasmutera da d all' a tanto il lustro si trasmutera da c a n.

28.  In MS A 10v, Leonardo defines pariete as "una linia perpendiculare, la quale si figura dinanzi al punto comune, dove si congiugnie il concorso delle piramide; e ffa questa pariete col detto punto quello medesimo ofizio che ffarebbe uno vetro piano, per lo quale tu riguardando varie cose, su ve le disegniassi." The drawing shows a intersection through the visual pyramid. Zaccolini here uses the word in this sense.

29.  Kenneth Keele, Leonardo da Vinci's Elements of the Science of Man, New York: Academic Press, 1983, 55, gives this translation of the entire passage: "Let ab be a mirror and the object seen in the mirror be c. Just as c sees all the parts of the mirror so all the parts of the mirror see c. Therefore c is all in the whole mirror because it is in all its parts; and it is all in each part because it is seen in as many different parts as there are different positions of the viewer. That is, if the object c is in n it appears as much behind as it is away [from the mirror]; therefore c appears to be at d. And whoever is at f seeing the thing d sees it through a straight line, therefore d is on the part of the mirror e. And whoever is at m will see d at t." The Italian critical transcription is my own based upon the diplomatic transcription in Ravaisson-Mollien, I, 1881. Another passage on luster in A 19r presents the idea that the rays of light hit and reflect from a plane surface through equal angles.

30. Another argument is based upon Zaccolini's use of the same letters: AB for the vertical illuminated surface, C for the light source, D for the image of the light source behind the surface, and M for the position of the eye. His language, however, is different ("nondimeno di continuo l'apparenza dell'imagine non mutandosi di sito si vedrà apparire in D altretanto di la quanto sarà il luminoso di quà della superficie per essere tale il temperamento della distanza del lume), leaving inconclusive the argument for intertextual dependency.


Poniamo che a b sia la pictura vista, e che d sia il lume, Dico, che se ti porrai infra c e, male coprenderai la pittura, e massime se sia fatta a olio o veramete verniciata, perche avra lustro e fia quasi di natura di specchio, e per questa cagione quato piu t'accosterai al puto c, meno vedrai perche quivi risaltano i razzi del lume, madato dalla finestra alla pittura: E se ti porrai infra e d li fia bene operata la tua vista, e massime quato piu t'appresserai al punto d, perche quello loco e meno participate di detta percussione de'razzi riflessi.

32.  Leonardo's passage should be recognized a new application of existing scientific principles, for Ibn al-Haytham, Witelo, Pecham, and many other optical treatises contained discussion and diagrams on how to find the point of reflection in a spherical mirror, which was shown to depend upon the location of the observer as well as the angle of incidence of the luminous rays. It is also a transformation of precepts in the Quattrocento art literature in which the viewer is advised to arrange himself and the objects to be drawn such that the light illuminates them obliquely. Thus see MS A 23r entitled "How the painter should position himself [in relation] to the light with its relief," (CU 43v-44, Mc 133, Lu 103): / Let ab be the window, m the point of light. I say that on whichever side the painter stands, that he will be well placed provided that the eye is between the shaded and luminous part of the body which he is drawing. And this place you will find by putting yourself between the point m and the division between the shadow and the light on the body to be drawn." (Translation by Veltman, 336).

See also Cennino Cennini, Il Libro dell'Arte, Ed. by Franco Brunello, Vicenza: Neri Pozza, 1982, chapter 9, pp. 10-11.

33.  This point was first made by Elizabeth Cropper, "Poussin and Leonardo: The Evidence of the Zaccolini Manuscripts," Art Bulletin, 62, 1980, 570-583.

34.  QUALE REGOLA SI DE' DARE A PUTTI PITTORI. Noi conosciamo chiaramete che la vista e delle veloci operationi che sia, ed in un puto vede ifinite forme: niete di meno no coprende se non una cosa per volta; Poniamo caso tu lettore guarderai in una occhiata tutta questa carta scritta, e subito giudicherai quella esser piena di varie lettere, ma non conoscierai in questo tepo che le lettere sieno, ne che voglino dire, ode ti bisogna fare a parola a parola verso per uerso, a voler avere notitia d'esse lettere;...

35.  Così dico a te il quale la nature volgie a questa arte, se vuoi aver vera notitia delle forme delle cose, comincierai alle particule di quelle e non andare alla seconda, se prima non ai bene nella memorie e nella pratica la prima; e se altro farai, gitterai via il tempo o veramente allungherai assai lo studio. E ricordati ch'impari prima la deligenza che la prestezza.

36.  A. I. Sabra, The Optics of Ibn al-Haytham, Studies of the Warburg Institute, 40, London: Warburg Institute, University of London, 1989, Book II, chapter 4. See also the commentary by Sabra in vol. 2, 103-4, and his earlier article, "Sensation and inference in Alhazen's theory of visual perception," in Perception: Philosophical and Scientific Themes and Variations, Machamer and Turnbull, eds., Columbus: OSU Press, 1978, 160-85.

37.  Ibn al-Haytham, Book I, ch 6.

38.  Ibn al-Haytham, Book II, chapter 4, 5-10.

39.  Friedrich Risner, Ed., Opticae thesaurus, Basel, 1572; with introduction by David Lindberg, NY: Johnson Reprint, 1972.

40.  Leonardo's main sources were Bacon and Pecham. Eugenio Garin, "Il problema delle fonti del pensiero di Leonardo," La cultura filosofica del Rinascimento italiano, Florence: Sansoni, 1961, 388-401; and Vasco Ronchi, "Leonardo e l'ottica," Leonardo. Saggi e ricerche a cura del Comitato Nazionale per le onoranze a Leonardo da Vinci nel quinto centenario della nascita, Rome, 1954, 161-85, have argued that his language indicates a second-hand knowledge of Alhazen and Witelo, possibly through compendia but not excluding a manuscript translation. On the translation known to Ghiberti, see Graziella Federici Vescovini, "Contribuito per la storia della fortuna di Alhazen in Italia: Il Volgarizzamento del MS. Vat. 4595 e il "Commentario Terzo" del Ghiberti," Rinascimento, ser. 2, 5, 1965, pp. 17-49.; and "Il problema delle fonti ottiche medievali del Commentario Terzo di Lorenzo Ghiberti," in Lorenzo Ghiberti nel suo tempo. Atti del convegno internazionale di studi, 1978, 2 vols., Florence: Olschki, 1980, pp. 349-387.

41.  See Thomas Frangenberg, "The Image and the Moving Eye: Jean Pélerin (Viator) to Guidobaldo del Monte," JWCI 49, 1986, 150-171. These ideas on two ways of seeing find an echo in Poussin's theory, for which see Carl Goldstein, "The Meaning of Poussin's letter to De Noyers," Burlington Magazine, 108, 1966, 233-237; and in De Pile's theory, for which see Thomas Puttfarken, Roger De Piles' Theory of Art, New Haven: Yale UP, 1985. I plan to treat this issue more fully in an article on visual perception in art theory.

42.  Ibn al-Haytham mentions written words in Book 2, ch. 3, 15, 128 among a list of other things an examples of visual things perceived by judgement and inference rather than pure sensation.

43.  Pedretti Commentary, I, 39n, suggested that Zaccolini may have known the Codex Casanatense 968 because of a note on the last folio (188a) which he has transcribed as "domanda Zaccolini." Steinitz, 1958, 47 and 95, suggested that he used one of the Barberini copies because of a similarity in the title cited by Cassiano. Both are possibilities, but the note in the Codex Casanatense merely shows that its owner knew Zaccolini; there is no way to decide which copy or copies Zaccolini consulted.

44.  Pedretti, Commentary, II, 396-7.

45.  Laur. Ash. 12121, fol. 2v.

46.  Bell, 1985, 250. Joe Connors has suggested that this passage in Cassiano's Montpellier biography ought to read: "...fa racconto d'haver particolarment in Napoli servito di disegni e modelli in più Chiese, come quella degli Ap[osto]li..." {instead of Agli [Angeli] as previously transcribed}.

47.  Luca Beltrami, "La villa di Castellazzo dei Conti Sormani-Busca," Ville e Castelli d'Italia, Lombardia e Laghi, Milan, 1907, 65-82.