Reflections on Art
Scientists debate whether the old
masters used optical aids
Peter Weiss
Like a defense lawyer in court, David G. Stork
was eager to know whether his closing argument
was winning over his audience. Would a jury vote
to convict? Stork asked the group assembled at
NASA Goddard Space Flight Center early this
month. None of the of the 100 or so people in the
Greenbelt, Md.–facility raised a
hand—just the response that Stork, chief
scientist of Ricoh Innovations in Menlo Park,
Calif., was hoping for.
Stork is no lawyer, but he definitely has a
group of people to defend. An investigator of
pattern recognition and an amateur artist, he's
on a mission to scientifically disprove the
assertion by renowned British-born artist David
Hockney that many of Europe's greatest artists of
the 15th and 16th centuries secretly used mirrors
or lenses to project traceable images onto their
canvases and thereby achieve the arresting
realism of their paintings.
First publicized in a New Yorker
article in January 2000, Hockney's proposal
jolted the art world and has received wide
attention from the media and general public.
Although Hockney recoils at the suggestion, many
people interpret his hypothesis as an accusation
that the old masters cheated.
The theory "touches some very raw nerves
as to what we think art and artists are
about," says art historian and Hockney
colleague Martin Kemp of Oxford University in
England. Optical aids such as slide projectors
are in widespread use today among painters, but
art lovers typically revere the superb realism
that Renaissance masters achieved without the
apparent use of such devices.
In addition to the mass media coverage of his
radical proposal, Hockney has made a documentary
film on the topic and even published a book, Secret
Knowledge: Rediscovering the Lost Techniques of
the Old Masters (2001, Thames & Hudson,
Viking Studio).
That the Goddard audience was wary of
Hockney's thesis was particularly gratifying to
Stork. That's because a year ago, art aficionado
and Hockney collaborator Charles M. Falco, an
optics professor at the University of Arizona in
Tucson, had presented the scientific case for
Hockney's proposal from that same Goddard
rostrum. At the end of his talk, Falco, too, had
polled the audience to see whether it was with or
against Hockney. By a show of hands, he says, 97
out of 100 listeners had declared themselves
convinced of the Hockney hypothesis.
Falco had volunteered his scientific services
to the artist after reading the New Yorker
article. The optics specialist developed nearly
all of the scientific evidence supporting
Hockney's original idea that many Renaissance
paintings are simply too precise to have been
done strictly by eye.
"I had the optics training to add the
scientific information to what [Hockney] had
seen," Falco explains. "It took both
[visual and scientific evidence] to make a
compelling argument." For instance, Falco
used the sizes of objects and people in the
paintings to calculate diameters, focal lengths,
and other characteristics of lenses and mirrors
that might have been used to project those forms.
In scientific circles, Falco's ideas have been
warmly received, except by a few vocal critics
such as Stork and Christopher W. Tyler of the
Smith Kettlewell Eye Institute in San Francisco.
Tyler calls the idea that optics were used in the
1500s and earlier "just storytelling."
Particularly galling, he and other critics say,
is the absence of any clear evidence from that
time that the optical devices available could
produce the kind of images Hockney claims the
masters used.
In turn, Falco derides the objections raised
by Stork and Tyler as unworthy of scholarly
debate. Their criticisms are "an
anomaly," Falco says.
In recent talks and publications, Hockney,
Falco, Stork, and Tyler have taken an especially
close look at a few Renaissance artworks. Much of
the discussion has focused on two paintings:
"Husband
and Wife" by Lorenzo Lotto and "Portrait
of Giovanni Arnolfini and His Wife" by
Jan van Eyck. Depending on the analyst's point of
view, even the same observations regarding those
paintings lead to startlingly different
conclusions.
Called on the carpet
Hockney and Falco have dubbed Lotto's painting
the Rosetta stone of their "opticality"
theory. Completed in approximately 1525, the
painting depicts a man and a woman seated at a
table covered by a small oriental rug.
What Hockney and Falco consider so telling
about this masterpiece is the curious distortion
of a foreshortened, octagonal pattern in the
front-center portion of the rug. The octagon is
formed by a kind of train-track motif that jogs
around a flower-blossom design. Hockney noticed
that the octagon becomes indistinct—like an
out-of-focus portion of a photograph—as it
recedes from the viewer.
The octagon's blurring is just the sort of
distortion that someone might see in a projection
of the rug by a concave mirror, Falco contends.
Moreover, it's a visual effect that an artist
looking with his eyes alone wouldn't see because
human eyes automatically refocus as they range
over a scene.
Falco has computed, down to the millimeter,
just how Lotto might have used a mirror. To
reproduce the complex details of the rug, the
painter would have positioned a mirror roughly a
meter and a half from the edge of the table at
which his models were sitting, Falco calculates.
Then, by placing himself to the side and about
halfway between models and mirror, Lotto could
have bounced a traceable image directly onto his
easel.
Apparent mistakes by the artist in rendering
the image in proper perspective strengthen that
supposition, says Falco. According to the
principles of geometric perspective, parallel
lines appear to converge at a single point in
space, known as the vanishing point, as they
recede from the viewer. However, a short way back
from the edge of the table depicted in
"Husband and Wife," some of the
presumably parallel lines of the train-track
motif converge to a vanishing point different
from that of other parallel lines in the motif.
That's easily explained, Falco argues, because
a mirror wouldn't be able to project the whole
rug pattern in focus at once. He calculates that
Lotto twice would have had to shift the mirror a
bit further back from the table in order to
refocus on details of the rug closer to the
background figures. Each time, if the artist
misaligned the mirror even slightly, the
vanishing point would shift.
There's a simpler explanation, claims Tyler,
who finds a hodgepodge of vanishing points in
Lotto's painting. This multiplicity of
perspectives suggests that Lotto painted
freehand, not worrying about getting the
perspective exact, as he would have done were he
using an optical aid, Tyler says.
In another experiment to test whether the
rug's octagon was drawn in proper perspective,
Tyler scanned the painting into a computer and
used Photoshop, a popular image-processing
software program, to digitally reorient the
rug-covered tabletop to look as if it were seen
from directly above instead of at an angle. With
the perspective removed, the octagon appeared
asymmetric. Tyler says this suggests that Lotto
botched the perspective in the first
place—further evidence that the rug was
painted by eye instead of reproduced optically.
Tyler unveiled his findings last October at
the annual meeting of the Society for Literature
and Science in Pasadena, Calif. He also has
posted an online report of his investigation (http://www.diatrope.com/hockney.html).
In Falco's view, however, Tyler
"completely blew the analysis." In his
own Photoshop experiment, Falco treated the
octagon as if it were composed of several pieces.
That's because each time Lotto would have moved
the mirror to bring a portion of the octagon into
focus, he also would have automatically changed
the magnification of the projected image, the
Arizona scientist explains. Indeed, if the
octagon's pieces are each resized adequately,
"the octagon fits the entire Lotto
tablecloth pattern to plus or minus a percent.
It's quite stunning," Falco says.
Even granting the thesis that Lotto used a
concave mirror to paint "Husband and
Wife," a mystery would remain: Why,
ultimately, would Lotto have left a blurry
section of the octagon in the painting? Falco and
Hockney conclude that the refocusing steps led to
several separately magnified octagon pieces that
Lotto couldn't completely reconcile. So the
artist fudged the details as best he could to
minimize the visual impact.
To Tyler, given that the octagon is such a
noticeable feature of the painting, the
refocusing explanation is farfetched. Had Lotto
enjoyed the benefit of a projection mirror, he
would have arranged his set-up to capture that
figure correctly, Tyler argues. "The octagon
was the one thing he would have needed the lens
for, so he would get it right," he says. A
better explanation, Tyler suggests, is that Lotto
painted the rug freehand without fretting too
much about the details.
All that glitters
If it's controversial to claim that Lorenzo
Lotto used optical aids, then it's even more so
to say the same of Jan van Eyck, a Flemish artist
who was painting a century before Lotto.
Nonetheless, in his book, Hockney argues that van
Eyck may have used a concave mirror to create his
famous 1434 portrait of the local merchant
Giovanni Arnolfini and his wife.
In the book, in television interviews, and on
Web pages, Hockney and Falco have argued that van
Eyck would have needed a mirror or lens to render
so faithfully the chandelier depicted in the
portrait.
To Hockney's eye, the chandelier is in
"perfect perspective," he told a 60
Minutes interviewer. However, by identifying
points on the chandelier that lie along parallel
lines and then plotting those lines by computer
over a reproduction of the chandelier image,
Stork has determined that the lines don't merge
to the expected vanishing points. "Wham!
What a mess," he declares, showing a slide
of van Eyck's chandelier covered with a jumble of
colored lines. "It's in terrible
perspective," he says. And that, Stork
argues, is evidence that van Eyck didn't use a
mirror.
The painted chandelier's arms also fail
another test. Were the arms identical, lines
drawn through the same features of each arm
should meet at the chandelier's axis of rotation.
That's not the case with the couple's chandelier,
Stork finds.
Both Hockney and Falco also have drawn
attention to a convex mirror that appears in the
painting on the back wall of the room in which
the couple stands. Had van Eyck flipped over that
mirror, they suggest, the painter could have
created the optical equipment required to make
the painting.
Yet Stork determined the probable focal length
of a concave mirror made by inverting and
silvering the convex mirror shown in the
painting. For instance, by computer-correcting
the reflection painted, he found that the focal
length of the mirror would have been too short to
project images of Arnolfini and his wife and
other features of the painting. This mismatch, he
says, militates against the Hockney-Falco claim
that the painter relied on optical aids.
Stork presented his challenges to the
chandelier and mirror claims in his talk at
Goddard, which also ranged over several other
paintings, and other criticisms of the
Hockney-Falco thesis.
For instance, to explain the sudden blossoming
in the early 1400s of a painting style that's
almost photorealism, Stork recommends alternative
explanations to optical technology. For example,
the advent of oil paints and the control they
offered artists are well documented in the
historical record.
Not that any of these arguments are convincing
the father of the opticality theory. "Mr.
Stork doesn't really change my view at all,"
says Hockney.
Even so, Stork has scored some points.
Hockney-supporter Kemp rates Stork's chandelier
deconstruction as "pretty convincing."
So does H. John Wood, lead optical engineer for
the Hubble Space Telescope, who heard Stork's
argument at Goddard. Both Wood and Kemp say they
still find the Hockney-Falco theory persuasive
but not convincing beyond the reasonable shadow
of a doubt.
With his hypothesis now supported and
challenged by technical analyses, Hockney muses
about whether science can ever settle the issue.
After all, he arrived at his hunch about optics
by looking at paintings and, later, tested it by
trying out optical devices in his own art.
"The only way you'd know [whether those
devices were used] is by looking at
pictures," he says. To him, the photographic
style that started showing up in the early 15th
century is a dead giveaway that the old masters
used optical technology.
Now that he has sparked an art-history debate
among scientists, Hockney is retreating from the
fray. "I've gone back to painting now,"
Hockney says. "I'm bored with the optical
view of the world."
********
References and Sources for this Article
References:
Hockney, D., and C.M. Falco. 2000. Optical
insights into Renaissance art. Optics &
Photonics News 11(July):52-59.
Further Readings:
Carrell, J.L. 2002. Mirror images. Smithsonian
(February):76-82. Available at http://www.smithsonianmag.si.edu/smithsonian/issues02/feb02/hockney.html.
Hockney, D. 2001. Secret Knowledge:
Rediscovering the Lost Techniques of the Old
Masters. New York: Viking.
Weschler, L. 2000. The looking glass. New
Yorker. (July 31):65-75. Available at http://www.newyorker.com/archive/content/?011126fr_archive02.
______. 2002. Through the looking glass:
Further adventures in opticality with David
Hockney. Artkrush. Available at http://www.artkrush.com/thearticles/011_woa_weschleronhockney/index.asp.
Additional information about the Art &
Optics conference devoted to David Hockney's
theory can be found at http://www.artandoptics.com/.
Further information about David Hockney's
theory can be found at http://webexhibits.org/hockneyoptics/.
Sources:
Charles M. Falco
Optical Sciences
G-S Building
P.O. Box 21007
University of Arizona
Tucson, AZ 85721-0077
Web site: http://www.optics.arizona.edu/ssd/FAQ.html.
Martin Kemp
Department of the History of Art
Littlegate House
St. Ebbes
Oxford OX1 1PT
United Kingdom
David G. Stork
RICOH Innovations, Inc.
2882 Sand Hill Road
Suite 115
Menlo Park, CA 94025-7054
Christopher W. Tyler
Smith-Kettlewell Eye Research Institute
2318 Fillmore Street
San Francisco, CA 94115
H. John Wood
NASA-GSFC
Optics Branch
Mail Code 551
Greenbelt, MD 20771
From Science News, Vol. 163, No. 22,
May 31, 2003, p. 346.
From http://www.phschool.com/science/science_news/articles/reflection_on_art.html
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AUTHOR:
David G. Stork