Leonardo Studies II · Chapter 7 of 18
Part Two, Chapter 1: Definitions and Categories
1. Introduction 2. Light and Sight 3. Categories of Light 4. Categories of Shade
5. Lustre 6. Colour 7. Darkness 8. Conclusions
1. Introduction
Leonardo's fascination with light and shade relates both to his painting practice and his optical theory. As has been shown elsewhere (Vol. One, Part Three), light and shade, or chiaroscuro as he terms it, makes possible the drawing of muscles (CU50, TPL42, 1505-1510), provides a sense of relief or depth in objects (A96v, BN 2038 16v, CU847, TPL667, 1492, CU844, TPL716, 1508-1510) and makes figures appear life-like (A100r, BN 1038 20r, 1492). For this reason he makes chiaroscuro the second principle of his painting practice (CU4, TPL5, 1500-1505), and describes it as the "excellence" of that science (CU840, TPL671, 1508-1510).1
He believes that the properties of light are analogous to those of sight. This is why his physics of light and shade involves many themes that relate directly to his theories of vision. Hence it will be useful to examine these light-sight analogies before considering his definitions and categories of light, shade, lustre and darkness. He also makes reference to seven books on light and shade. Richter, in the Literary Works make a rough attempt at reconstructing six of these books.2 Pedretti has taken this one step further.3 We shall show, however, that Leonardo's outline can be taken more seriously; that all seven books, plus an eighth on movement can be reconstructed and that his studies in this domain involve a much more coherent structure than has hitherto been imagined. Moreover, these studies reveal an unexpected amount of systematic experimental research.
In a subsequent chapter it will be shown that his studies of the camera obscura go hand in hand with these studies on light and shade. For instance, he makes systematic studies of different sizes and shapes of apertures in order to discern more complex properties of light and shade. He demonstrates that the image in a camera obscura sometimes resembles the aperture, and at other times assumes the shape of the original light source. He also discovers that, under certain conditions, the boundaries between light and shade are fully obscured, leaving a spectrum of gradations. In his early writings he claimed that light and shade were more difficult than design (disegno, A81r, BN 2038 1r). His new findings convince him that the boundaries between light and shade are most difficult of all (CU106, TPL121, 1505-1510).
Having considered his studies of light and shade (part two), it will be shown how these studies serve as a basis for his physiology of vision (part three): how he compares the aperture of a camera obscura with the aperture of an eye, and how his work on gradations of light and shade influences his claims that the eye cannot perceive boundaries clearly.
2. Light and Sight
Leonardo's conviction that the properties of light and sight are fully analogous explains the close links between his physics of light and shade and physiology of vision. His earliest extant reference to this analogy occurs on W19147-19148v, (K/P 22v, c.1489-1490) where he notes that: "
Light does the same, because in the effects of its lines and maximally in the works of perspective it is very similar to the eye." Some two years later he explores this theme at length on CA204vb (c.1492):
(Sight)
Light in the function of perspective is no different from the eye. The reason that light is no
different from the eye as concerns occluding that which is behind the first object, is this:
you know that as concerns speed of motion and the concourse of straight lines, the visual
ray and the luminous ray are the same....
Directly following he gives a demonstration:
For example, if you place a coin...near the eye, that...space which occurs between the coin
and the extremity of the site, the more that it is capable of a greater interval, the greater will
be that part of the extremity of the site that is not seen by the eye and [hence] the closer that
the coin is to the eye, the more will the extremity of the site be occluded.
He expands on this in the next paragraph:
On Light
The same will occur in light, because in bringing a coin nearer or further from this light you
will see the shadow increasing or decreasing on the opposite wall. And if you wish an
example, do it in this form: have placed in a room many bodies of various objects. Then
take in your hand a long pole with charcoal at the end and with this mark off on the ground
and on the walls...all the [projected] boundaries of the panels which appear beyond the
[actual] boundaries of the panels.
In the right-hand margin alongside this he writes the headings: "On the eye," and "On light." In the paragraph that follows his description continues:
Then at this same distance and height take a light and you will observe that the shadows of the said bodies occupy as much of the wall, as is that part which finds itself included within the marks made by the charcoal at the end of the stick.
Next he describes a related demonstration:
Experiment.
If you wish to see clearly a similar experiment place a lamp at the head of a table...then go backwards somewhat and you will observe all the shadows of the objects which are between the wall and the light stamped by shadow...in the form of the objects...and all the lines of their length directed to the point where the light is.
Then bring your eye nearer to this light, producing such shadow with the edge of a knife so as not to offend the eye and you will see all the objects positioned opposite without shadow and the shadows which were on the panels of the eye will be occluded at the eye by the interposed objects.
In short, the area thrown into shadow by candlelight coincides with the area occluded by the same object as a result of the visual angle. He develops this idea on CA241vd (1508-1510):
In all the functions of shade spherical light is as the eye in its visual power, because one
opaque sphere interposed between the eye and a panel will occlude as much of the light on
that panel as would the eye.
He pursues this analogy on CA195v (c.1510):
A window does the same on each side whether above or below and likewise on one side as
one the other where it borders on the dark wall.
And the species that enter the pupil do the same and they are thrown to the right and left,
intersected behind the interposed object.
This close analogy between geometrical light rays and visual rays explains (a) why various folies with notes on the physics of light and shade also deal with the physiology of vision and (b) why he continues to use "perspective" in its mediaeval sense meaning "vision" as, for example, on W19037v (K/P 81v, 1489-1490), when describing his anatomical programme, he refers to "perspective, through the action of the eye" or on CA119va (c.1492) where he makes the heading: "Premium to perspective: that is, on the function of the eye." Leonardo takes this analogy further. In his mind the geometry of visual rays, the geometry of rays of light and shade and the geometry of rays of linear perspective are all equivalent. Hence his claim in a draft note on BM103v (1490-1495) that "all the functions of lights are similar to those of the eye as concerns the perspective of painters." On A103v(BN 2038 23v) he claims that in "all cases of linear perspective it is similar to light." For this reason he is usually not concerned with distinguishing clearly between perspective (a) in the sense of "optics" and (b) in the sense of "linear perspective," as is evidenced by his definition of perspective on A3r (1492):
as a demonstrative reason by means of which experience confirms that all things send their
similitudes to the eye by pyramidal lines.
For the same reason, he deals interchangeably with problems of vision, linear perspective, and light and shade with respect to anamorphosis in his treatise on perspective on A36v-A42v analysed earlier (see Vol. 1, Part I:2 ). Moreover, this light-sight analogy explains why a number of folios dealing with rays of light from the sun also contain notes on vision (see below pp. figs. ). Indeed, once we understand that analogy is a key to Leonardo's organization, much of the apparent confusion of his notebooks disappears.
3. Categories of Sight
Leonardo has practically no definitions of light. He calls light the chaser of darkness of CA116rb (1492). He notes that light makes objects evident (dimostra), whereas shade hides them (A102r, BN 2038 22v, 1492). He does not dwell on the metaphysics of light. The importance he attaches to the subject is, nonetheless, clear from the opening passage of Pecham's Perspectiva communis that he copies in translation on cA203ra (1492).
Among the study of natural considerations, light delights its contemplators most. Among the great things of mathematics the certainty of the demonstrations raises most sublimely the mind of the investigators. Hence perspective is to be proposed above all the traditions and humane disciplines, in the domain of which the luminous ray, complicated by the modes of demonstrations, finds the glory of both mathematics and physics, decorated by the flowers of each.
Leonardo is more interested in various categories of light. In the Mediaeval optical tradition one had distinguished between primary (direct) and secondary (reflected light.4 There had also been a distinction between lux (A102r, BN 2038 22r, 1492). He also makes a distinction between primitive and derived lights which, according to his definition on C16v (1490), would correspond to the mediaeval terms primary and secondary light: “That light is said to be primitive which primarily lights umbrous objects and derived is said to be that which is reflected from those parts.”
On CU158 (TPL157, C.1492) he reformulates this definition, now substituting "original" for "primitive":
...lights are of two kinds (nature): one is called original, the other derivative. Original I
claim to be that which derives from the flame of a fire or from the light of the sun or the air.
Derived light is reflected light.
In another passage on BM171r (c.1492) he reverts to his earlier terms, primary and derived, but now defines them somewhat differently under the heading:
How lights are of two kinds, the one separate, the other joined to bodies.
Separate is that which illumines the body: joined is that part of the body illumined by that
Alberti in his On Painting had distinguished between light from the stars, i.e. sun, moon, enus, etc. and light from fires.5 He had also mentioned reflected light. Leonardo takes these distinctions further. In an early note on BM 170r (1492), he distinguishes simply between free and restricted light (figs. ):
On A109r (BN 2038 29r, 1492) he develops this into a threefold distinction:
This evolves into a fourfold distinction on G3v (1515, cf. CU598, TPL663, c. 1510), under the heading:
Of Lights.
Elsewhere he is content to omit mention of transparent light and limit his discussion to three kinds as on CU866 (TPL754, 1508-1510):
On giving the necessary lights to illuminated objects in accordance with their sites.
And which shall also make the necessary remarks about this in its proper place.
A late reference to this threefold distinction is found on E3v (c.1513-1514) under the heading of:
Painting.
Of the 3 kinds of lights which illuminate opaque bodies.
This third variety of light here mentioned he had described in more detail on CU593 (TPL558, 1508-1510) in a passage entitled:
What is the difference between compound light and compound shade?
Hence Leonardo considers various categories of light: primitive (separate) and derived (joined); universal (free), particular (restricted), reflected, translucent and compound. As we shall see some of these categories recur in his discussion of shade.
4. Categories of Shade
Pecham had claimed that "shadows are diminished light."6 "Shade, writes Leonardo on C14v (1490-1491), "is a diminution of light." He returns to this definition in a paraphrase on W19152v (K/P118v, C.1508-1510):
Shade is diminished light mediated by the opposition of an opaque body.
Shade is the substitution of the luminous ray that has been intersected by an opaque (body].
On W19076r (K/P167r, c.1513) this definition becomes the first in a series of alternatives:
Shade is of infinite obscurity and of infinite diminution of this obscurity.
Shade is a pronouncement by bodies of their shapes.
The shapes of bodies will not give knowledge (notitia) of their quality without shade.
He returns to the first of these definitions on E32v (1513-1514, CU580, TPL550a, 1513-1514): "Shade is diminution of light." A variant of this basic definition is found on A102r (BN 2038 22r, CU577, TPL549c, 1492): "Shade is privation of light and only the opposition of dense bodies opposite luminous rays: shade is of the nature of darkness...." One of these definitions he repeats on CA116rb (c.1498 or 1495-1497): "Shade is privation of light." On CU604 (TPL660b, 1508-1510) he combines two of these basic definitions: "Shade is a diminution or a privation of light." At other times as on Mad II 25r (c.1503-1504) he defines darkness as "a privation of light" claiming that "shade is an alleviation of light. And there is no darkness where there is not some exhalation of air." He returns to this formulation on CA207ra (c.1508-1512):
Darkness is a privation of light.
And shade is an alleviation of this light.
Shade is a mixture of darkness with light.
Shade is an alleviation of darkness and light.
A related version occurs on CU578 (TPL665, 1508-1510): "Darkness is a privation of light and light is a privation of darkness. Shade is a mixture of darkness with light." On A102r (BN 2038 22r, CU577, TPL549, 1492), he describes shade as being: " of greater power than light, because this prohibits and deprives objects entirely of light, and light can never hide the shade of bodies, that is, dense bodies." On CU582 (TPL556, 1508-1510) he provides yet another definition: "shade is said to be that where no part of the luminous body or illuminated body can see." On CA207ra (1508-1510) he drafts two further definitions:
Shadow in opaque bodies is percussion of the species of dark bodies.
These he crosses out and writes anew: "Shadow is a mixture of bright and dark and is of that much more or less darkness as the bright with which...it mixes itself will be of greater power." As in the case of light Leonardo considers various categories of shade. A straightforward solution is given on CU597 (TPL569, 1508-1510) in a passage entitled:
How many sorts of shade are there?
In the passage on BM171r (c.1492) cited above it was noted that just as he distinguishes between primitive and derived light, so too does he distinguish between primitive and derived shade (fig. ). In the extant notes this distinction first occurs on Triv 11v, 29r (c.1487-1490). He returns to it on C14v (1490) where he lists a number of basic definitions:
Primitive shade is that which attached to umbrous bodies.
Derivative shade is that which is detached from umbrous
bodies and passes through the air.
Repercussed shade is that which is surrounded by an illuminated
wall.
Simple shade is that which does not see any part of the
light that causes it.
Simple shade begins in that line which parts from the
boundaries of the luminous bodies ab [fig. 174).
In the introduction to his books on light and shade on CA250ra (c.1490) Leonardo drops the term "primitive" and refers instead to: "Original shadows since they are the first shadows which invest the bodies to which they are attached." He then goes on to note that:
He pursues these distinctions on A102r (BN 2038 22r, 1492) now referring to primitive shade as joined and derived shade as separate (figs. ):
What is the difference between shade joined with bodies and separated shade.
On CA116rb (1498 or 1495-1497) this theme is taken up anew in a draft:
Primitive shade is that part of the bodies which cannot be seen by light.
Derived shade...is only the percussion...of umbrous...rays.
Accompanying this passage is a diagram (fig. ) illustrating primitive and derived light and shade. Some years later he makes a passing reference to this distinction on CU585 (TPL570, 1505-1508): "The species of shadows are of two sorts, of which one is called primitive and the other derived." Almost as cursory is a passage on CU584 (TPL552, 1508-1510) entitled:
On shadow and its divisions.
In the late period he returns once more to these terms on E32v (1513-1514, cf. TPL553a, c.1508-1510):
Primitive shade always serves as a basis of derived shade.
The boundaries of derived shade are rectilinear.
On C14v (1490) he had referred to repercussed shade. On E32r (c.1513-1514) he returns to this concept, now calling it something else: " On corrupt shadows. Corrupt shadows are said to be those which are seen by a white wall or other luminous bodies." On CU759 (TPL573, 1505-1508) he subdivides the category of derived shade, in a passage headed:
What are the varieties of derivative shade?
As will be seen in the next chapter he further subdivides the first of these categories into shadows that increase with distance, those that remain constant and those that decrease with distance (figs. ). These basic categories are summarized in our Chart. 5. On CU588 (TPL572, 1505-1508) he considers another subdivision of primitive shade (figs. ):
In how many ways does primitive shade vary?
Primitive shade varies in two ways, of which the first is simple and the second is compound.
He returns to this distinction between simple and compound shade on BM248v (c.1508): "Simple shade is that which does not see any luminous body. Compound shade is that which is illuminated by one or more luminous bodies." On CU590, (TPL553, 1508-1510) he again describes these two kinds of shade in a passage headed:
On two species of shade and in how many parts they are divided.
In the passage immediately following on CU591-592 (TPL553a-b, 1508-1510) he divides simple shade further:
And the same is said of compound shade.
In other words, simple and compound shade have here become generic terms to which the categories primitive and derived are now subordinate, (see Chart 5). He returns once more to this basic distinction between simple and compound shade on CU582 (TPL557, 1508-1510):
What difference is there between simple and compound shade?
In addition to these categories of light and shade he also provides basic definitions of lustre, colour and darkness. Each of these will be considered in turn.
5. Lustre
Leonardo distinguishes between light and lustre in an early note on A113v (BN 2038 32v, 1492):
A pithy definition of lustre occurs on CU769 (TPL664, 1508-1510) under the heading:
On illumination and lustre.
Illumination is participation of light, and lustre is the mirroring of this light.
On CU774 (TPL775, 1508-1510) he develops this distinction between lights and lustre under the heading:
What is the difference between lustre and light?
He returns to this theme on E31v (CU780, TPL776, 1513-1514):
Of light and lustre.
In another late passage on G10r (c.1510-1511) he refers to lustre as an "accident" (fig. 175 ):
On the shadow of a leaf.
Elsewhere in this same treatise, on G24r (CU949, TPL886, c.1510-1511) he again refers to lustre as an "accident" but this time of colours:
Of the accidental colour of trees.
6. Colour
In Antiquity the problem of colour had been linked with philosophical debates concerning the visual process. Leon Battista Alberti, in his On Painting (1434), is aware of these philosophical debates but consciously avoids them.7 He alludes to theory, but emphasizes practice.
6.1 Black and White
With respect to black and white, for instance, Alberti notes that "the painter ought to be persuaded that white and black are not true colours but alterations of other colours"8 and at the same time treats them as if they were colours. Leonardo inherits this ambiguous approach which theoretically rejects and practically accepts black and white as colours. On CU783 (TPL692, 1508-1510), for example, he mentions in passing "if it can be said of white that it is a colour. On CU739 (TPL699, 1508-1510), he notes that "neither white nor black are colours." On F75r (CU204, TPL247, 1508), he goes further and sets out to show "why white is not a colour" (see below p. ). This leads him, on CU205 (TPL215, 1505-1510), to discuss white as the most receptive of colours because it is empty:
What is that surface that is most receptive of colours?
On F23r (1508) he notes, in passing, "no white or black is transparent."
6.2 Simple Colours
Nonetheless, in practical terms, he accepts black and white as simple colours, as on CU176 (TPL254, 1508-1510) where he lists six:
These simple colours he links with various elements:
His equivalents bear comparison with those of Alberti9, although the two authors disagree on the colour of earth (Chart 6). Leonardo makes a further list of simple colours on CU178 (TPL213, 1505-1510). Instead of six, he now mentions eight:
6.2 Compound Pigment Colours and Compound Coloured Lights
He goes on to describe how these basic colours can be mixed to produce further colours:
With these I begin mixtures, first white and black, then yellow and black, yellow and red, and since I here lack paper, I will wait to make such distinctions in my work with a long process which will be of great use and also most necessary. And such a description will be intermediate between the theory and practice of painting.
This leads to instructions concerning more complex mixtures of pigments (see below pp. ). Meanwhile, by 1492, he is studying how light passing through coloured glass becomes a different colour, as on CA126ra where, in connection with a camera obscura (fig. 156, see above pp. ), he notes: "how the point is cause of the base: ...put a coloured glass in front of a light and you will see the base tinged in this [colour]." On W19151v (K/P118v(B), 1508-1510) he describes how sunlight passing through both an azure and a yellow pane of glass produces a green light (see below pp. ). In such experiences he finds a new demonstration for the production of compound colours, as, for instance on CU176 (TPL254, 1508-1510):
This leads to a description of what happens in the case of various colours of glass:
As a result of such experiences he revises his list of simple colours. Azure and green, which he had at first described as simple (CU176, 178), he describes as compound on CU177 (TPL255, 1505-1510):
On colours.
6.3 Light and Colour
Such experiences make him ever more aware of the extent to which colour is determined by the intensity and colour of nearby light and shade. In the early period, as on CU208 (TPL259b, 1482), he believes that a colour can only be true, if it is not seen by other shadow or lustre:
Of true colour.
He restates this idea on CU725 (TPL694e, 1508-1510):
Meanwhile he is also exploring the conditions for true shade as, for example, on CU803 (TPL703, 1508-1510):
What is, in itself, the true shade of colours of bodies.
On CU197 (TPL203, 1505-1510) he reconsiders the conditions required for true colour:
He pursues this question of true colours on CU799 (TPL816, 1508-1510):
Precept.
The extent to which changes in light and shade are important depends in part on the original colour of the object. On CU787 (TPL636, 1508-1510), for instance, he points out that these changes are least in the case of black:
Which principle shade on the surface of bodies will have less difference from the luminous parts and which will have more?
On CU739 (TPL699, 1508-1510), he notes that these changes are greatest in the case of white:
What colours produce more variety between lights and shades?
He compares the effects of light and shade on white, black, green, azure and grey on CU783 (TPL692, 1508-1510):
Where and in what colour shadows lose the natural colour of the umbrous body more?
6.4 Light and Beauty
As early as 1492 he is aware that light also augments the beauty of a given colour and hence, on A112r (BN 20-38 33r, CU188, TPL210, 1492) he notes;
How the beauty of a colour must be in its light.
He reformulates this idea on CU187 (TPL207, 1505-1510):
On CU189 (TPL242c, 1505-1510), he restates this connection between light and beauty:
Of colours.
He states this idea more forcefully on CU762 (TPL768, 1508-1510):
What part of umbrous bodies will show their colours with a more excellent beauty?
In the period 1508-1510 he also explores which colours compliment one another as on CU182 (TPL253):
On colours.
In the late period he returns once more to the connection between light intensity and beauty in a longer passage on E18r (1513-1514) which opens under the heading:
He now introduces the objection of an:
Adversary.
This he counters with a:
Reply
Hence at a long distance all the shadows of the various colours appear of a same darkness.
Among bodies covered with light and shade the illuminated part shows its true colour.
6.5 Darkness and Colour
If greater light shows the truth of colours, greater darkness removes it. Alberti had expressed this corollary succinctly in his On Painting: "As shadow deepens the colours empty out and as the light increases the colours become more open and clear.10 Leonardo broaches this problem in passing in his "prophecies" on CA370ra (1497-1500):
Of the nights which do not know any colour.
He again mentions the effects of darkness on colour on CU194 (TPL201, 1505-1510):
Whether various colours can appear of a uniform darkness through a same shadow?
On CU696 (TPL715, 1508-1510) he pursues the question:
He reformulates this idea on CU740 (TPL713b, 1508-1510) in terms of black surfaces:
What surface makes less difference between bright and dark?
He mentions the problem once more on BM169r (c.1510): "Darkness (tenebre) tinges everything with its colour and the more a thing departs from this darkness, the more it is rendered of its true and natural colour." This idea he restates as a general rule on E30v (CU734, TPL592, 1513-1514):
Quality of shades.
Elsewhere in the same treatise, on E17v (1513-1514) he reformulates this in terms of two propositions:
5th All colours positioned in umbrous places appear to be
of equal darkness among one another.
6th But all colours positioned in luminous places never vary
from their essence.
6.7 Colour Conclusions
At the outset Leonardo probably intended to write an independent treatise on colour. By the period 1508-1510 he intended to annex this treatise on colour to his work on the rainbow at the end of his book on painting, as is clear from a note on W19076r (K/P167r):
This explains the close links between his notes on colours and discussions of the rainbow (see below pp. ), which links, in turn, confirm a shift in his thinking. By 1510 theoretical questions concerning the substance of colour are no longer of interest to him. For all practical purposes colour is now a phenomenon of varying light and shade. This is why most of his notes on colour emerge as two chapters of his Books on Light and Shade (see below pp. ).
7. Darkness
Leonardo defines darkness as a privation of light, sometimes strengthening this with adjectives such as "entire" (CU665, TPL810, 1505-1510). In the extant notes he repeats this basic definition at least ten times (see Chart 7). On most occasions he treats darkness as an absolute category and carefully distinguishes between shadow and darkness, as on G8r (c.1510-1515): "The shadows of plants are never black because where the air penetrates there cannot be darkness." On rare occasions, as on CA371rb (1510-1515), he suggests that there may also be gradations of darkness: “The percussion of derived shade in darkness is similar to the darkness of this derived shade, that is, the variety of its darkness.”
8. Conclusion
We have examined Leonardo's analogies between light and sight in order to explain the close parallels between his physics of light and shade and studies of vision. We have also outlined his definitions and categories of light, shade, lustre, colour and darkness were outlined. In the following chapter we shall show how he builds on these basic concepts in drafting his seven "books" on light and shade.