Ricoh Innovations and Stanford University
 David G. Stork
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Future discussions: From "Rosetta stone" to challenge paintings

The Hockney/Falco theory is nothing if not sweeping. The proponents are quite explicit that they are not illuminating mere curiosities in a handful of paintings (as might interest a graduate student and a small community of art historians) but instead advocating a radical reevaluation of the artistic methods over a span of several centuries. Hockney's book shows several dozen paintings by numerous painters over several centuries.

Paradoxically, if Hockney and Falco were to restrict their domain, say to a few specific paintings or to a few specific artists they would weaken their theory and make it more implausible (not to mention reduce the public's interest). For instance if it could be shown that an early Lotto "optical" painting was done without optics, then the likelihood that he needed to use optics for a different painting is thereby reduced (see below).

Because of the breadths of its claims, the theory then must be able to explain -- or at the very minimum, be consistent with -- other "optical" paintings in the period. Below I've posted four challenge paintings, all by artists enlisted by Hockney or Falco in support of their theory, that present a variety of difficulties for their theory. These are representative of a wide range of paintings of the time -- they are neither obscure nor "straw men." Any account of Renaissance painting must deal adequately with the creation of these masterpieces. I have dealt specifically with the most important paintings Hockney and Falco have hand-picked in support their theory. It is now only fair that they or their supporters address other Renaissance paintings picked by me.

1. In applying the Hockney/Falco theory to these paintings, it is important that the designs and explanations be specific, and include the locations of the concave mirror (and any plane mirrors), the number and type of light sources and whether they are artificial or sunlight, whether the first step was tracing a projected image in pencil and then rotating the canvas, and so on. I post these challenges for anyone to address. The best way to ensure that we are not deluding ourselves is to re-enact the proposed methods (as mentioned in the analysis of modern demonstrations, above) for A) and D), below. Note: artistic skill is not required for such demonstrations; the efforts of an enterprising science undergraduate or art school student should be adequate.

Rembrandt "Self portrait" (1658)

A) Rembrandt "Self portrait" (1658)

  • How do you get (very) bright light on Rembrandt's head (for extended periods) while keeping the canvas itself dark? Must Rembrandt dip his head in and out of a dark tent as he paints? Does he need to use a candle inside the tent to see his dim markings, as did Mr. Hockney in his BBC film?
  • How do you get (very) bright light on Rembrandt's head while also allowing him to stay dark adapted (i.e., keep his eyes in the dark and thus sensitive to the dim projected image that he will trace)? Given that an exposure to bright light even as short as two seconds requires several minutes of subsequent dark adaptation, how long does he take between brush strokes? How do you keep the illumination coming from roughly the same direction throughout the period it took Rembrandt to paint this?
  • How do you keep the reflection from the mirror confined to be nearly along the axis so as to avoid off-axis aberrations (the image degradation that plagues simple concave mirrors)?
  • Given that (to the best of my knowledge) all Rembrandt paintings, including self-portraits, have normal ("down") brushstrokes, how can he produce such downward brushstrokes in this painting? Must all his brushstrokes be "up" on the inverted camvas, so as to then appear "down" when the painting is re-oriented for display? Did Rembrandt trace a projected image (thereby leaving an underdrawing that could be be revealed by modern infra-red photography) and then paint over it in oil?
  • The best demonstration that such a self-portrait could indeed be painted using optical projections would be if Mr. Hockney or any other talented person painted (not drew) a self-portrait using illumination compatible with that from the 15th century -- yielding a painting whose underdrawing (tracing or none) could be compatible with evidence from the Rembrandt. In this way, myriad additional technical difficulties would become apparent. (It would, too, be helpful if he would paint a self-portrait by traditional non-optical means, so we could compare the qualities of the finished paintings.)

Michelangelo "Ceiling of the Sistine Chapel"

B) Michelangelo "Ceiling of the Sistine Chapel" (1508-12)

  • Given that the ceiling is well above every window in the Chapel, how do you reflect sunlight up through the scaffolding to the models and the mirror projection system? Alternatively, how do you support hundreds of candles or many bright lanterns that high? Very roughly, what would the cost be for candles during the four years of painting, and how would that compare with Michelangelo's salary?
  • How do you hold a concave mirror stable on a scaffolding over 60 feet high? Is it facing up? Where precisely are the models posing? How do you get robes to billow or the Almighty's beard to sweep, as if blown by wind?
  • How do you get the models close enough to the ceiling so as to project their image onto the ceiling? How do you hold a model for each putto still during the projection? (How do you get its mother to allow you to take her baby 60 feet above the Chapel floor?)
  • What is the effective projected image area on the ceiling, and how do you move the projection system to cover neighboring regions?

Leonardo "The Last Supper" (1498)

C) Leonardo "The Last Supper" (1498)

  • How do you get, through optics or other means, the images to be rightside up?
  • How do you get, through optics, straight lines and remarkably consistent single-point perspective across the 8.8 meter width of the painting?
  • Given that there is no access behind the wall, where, specifically, do you place the models, the mirror and the illumination needed for a projection in the dark Refectory of the Convent of Santa Maria delle Grazie?

Lotto "Angel of the Annunciation" (c. 1530)

D) Lotto "Angel of the Annunciation" (c. 1530)

  • The illumination is from quite a low angle. If it is sunlight, the period during which this direction holds is quite short. If the illumination is instead artificial light, how do we get (very) bright illumination needed for the optical projection?
  • How can the figure hold her pose -- off balance, supported by a single tiptoe -- during the projection?
  • How are the cast robe and floating waist band to hold their shape long enough for their projected image to be traced?

2. In good scholarly protocol, the next step must be to present the designs from 1 in a forum for comment and analysis by acknowledged scholars, such as peer-reviewed scholarly journal. Only in this way might subtleties and inconsistencies be caught.

Of course, to show that something could have been done does not imply that it was actually done! Thus solving most or all of the tasks in 1, while necessary, is not sufficient to justify acceptance of the Hockney/Falco theory. The next step could be to show how the challenge images could not have been done by traditional "eyeballing" methods -- or at the very least, that the eyeballing or other non-optical method is less plausible than Hockney and Falco's.

How might this be done? Up to now, the primary arguments against 'eyeballing' and non-optical methods have been

  1. Mr. Hockney's admission that since he cannot paint well enough to produce numerous Renaissance paintings unaided, then neither could the Renaissance painters themselves.
  2. There seemed to be a qualitative change in the art around 1430 that somehow seems too major to be due to non-optical methods.
  3. Implied technical arguments based on compatibility with the optical theory.

Point 1 is fine as inspiration and motivation, but as an argument it is of course fallacious. Today's foremost organists will willingly concede that they cannot improvise four-part fugues the way J. S. Bach did; today's foremost playwrights will willingly concede that they cannot write plays of the caliber of Shakespeare's; today's orators cannot match Cicero's eloquence; today's mnemonists cannot remember the volumes Homer could; and so on. It goes without saying that art students and apprentices in the 15th century spent more time on draftsmanship and life drawing than most of their 20th-century descendants, and for better or worse, such talents were more highly prized then than now. Bouguereau and Philip Pearlstein to take just two of many many examples, painted incredibly realistic "optical" paintings without the use of optical devices. (The fact that some representational artists such as Eakins employed optics such as photography for some paintings does not mean Lotto did.)

Even if we accept that there was an important change in the realism of European art at the beginning of the Renaissance (as I do), the only way argument 2 can be valid is if alternate explanations (e.g., the role of oil paint, Brunelleschi's revolutionary discovery of the laws of perspective in 1410-15, new social and economic pressures to record living patrons rather than dead idealized saints, alternate methods such as grids and pantographs) have been examined closely and found deficient. In fact, the methodological burden is upon supporters of the Hockney/Falco theory not just to propose another way in which Renaissance paintings could be created, but to disprove or show the implausibility of traditional explanations. This simply has not been done by the theory's supporters.

Argument 3 is of the general form: a) Here's are interesting anomalies in a painting (e.g., inconsistent vanishing points, "blur" and so forth in Lotto's "Husband and wife"), b) here's an explanation consistent with the optical hypothesis, therefore c), optics were used. There are at least three logical falacies in argument 3. First, there may be many explanations consistent with the data; I showed this (and more) in the Albergati portrait. Second, the proposed explanation might contradict yet other facts and hence be false; Tyler showed this of the Hockney/Falco theory with regard to the derived carpet design. Third, the preconditions of the theory might be invalid. Suppose I could explain all the phenomena perfectly and in detail by first assuming van Eyck had laser range finders and sonar; my theory would of course be false. Without corroboratory evidence for the existence of concave mirrors, many observers will at least worry that the Hockney/Falco theory is wrong on this account. At the very least, we can conclude that Hockney and Falco's most detailed analyses have yet to find broad scholarly support, and thus even for "Rosetta stone-like" paintings their theory hasn't progressed through stage 2.

3. The next step is to look for supporting evidence for the required optical elements. For instance, suppose someone were to design a method and arrangement of mirrors for the Sistine Chapel. We would then have to ask why no one in the Vatican recorded use of optics, or no appropriate mirrors appear in Vatican records.

4. The final step is to see if the resulting explanations mean that using optics was better -- faster, higher-quality "optical" images, cheaper -- than non-optical methods.

For instance, imagine that someone designs an optical setup by which Rembrandt could have created a self portrait (1). Suppose, too, that through open scholarly debate no one finds a significant flaw in that design and method (2). Suppose, moreover, that we find conclusive evidence that Rembrandt in fact had the requisite optical devices (3). We might nevertheless reject the optical hypothesis because it required Rembrandt to take unduly long (required frequent dark adaptation) led to images of lower fidelity, was too expensive (required too many candles), or other such reason.

Summary: Because Hockney and Falco state their theory applies to such a broad range of paintings over centuries, it should be able to account for difficult cases ("challenge images") chosen by others, not just those picked by themselves (e.g., "Rosetta stone"). The four challeng images provided here are meant to propel the discussion and clarify the explanatory power of the theory.


A new theory?

At the New York symposium, Hockney put forth a modified theory concerning optical projections, one that was merely alluded to in his book: that it wasn't necessary for later Renaissance painters to actually employ optical projections during the creation of their art -- that merely experiencing projected images was sufficient to change their way of seeing and thus their art. In his phrase about such projected images, "to see them is to use them" -- or even (implicitly) "to see a painting by someone else who has seen them is to use them." This is a very curious thesis and I don't know how one could reasonably approach it, or distinguish it from ones based upon seeing a well-constructed geometrical perspective drawing, or even from not having seen such an image at all, or from the absurd claim that painters started painting more "optically" after learning of the Hussite Revolt of 1420-1434. In short, I don't see how this new theory is "falsifiable" (to use Karl Popper's term). Unless and until anyone can suggest a way we could in principle test this new theory and distinguish it from others, it will lie beyond the realm of scholarly discourse.

Summary: Before we can address a new, modified theory, it must itself be cast as a theory with testable empirical predictions and consequences that differ from other plausible theories.


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