Depending on the tilt of the plate with respect to the sun, you might
accidentally discover the “pseudoscopic” image of the “V,” and it may
appear to float *above* the surface of the plastic. Tilt the plate to
bring the far edge up and towards you and you’ll then find the
“orthoscopic” image floating deep within the plate.

If you had inscribed your entire name on the plastic, you’d now be seeing
it down there within the surface. (hint hint!) It’s also possible to draw
complicated 3D objects by varying the compass spacing as you slowly draw
glowing lines one point at a time. The distance between the compass
points controls the depth of the hologram-dots you are making. I’ve been
drawing cubes, pyramids, and holes with glowing stars at the bottom. As
with conventional holograms, opacity effects can be achieved by
controlling the location of the endpoints of the scratches. And many
other sophisticated effects produced by conventional rainbow holography
can be duplicated in black plastic and scratch patterns.

CHANCE FAVORS THE *CURIOUS,PLAYFUL* MIND

All this all started while I was walking along the rows of cars in the
parking lot at work. I noticed this one black station wagon hood that had
a number of glowing highlights created by the sunlight. Typical science
hobbyist response: I stopped and began playing with them. I was moving my
head back and forth in order to make them slide around, when I noticed
that some of the highlights seemed to exist a few inches WITHIN the
surface of the car hood. I’ve long been interested in stereo images, so I
started examining these “deep” highlights in detail. Some of the larger
ones had an interesting structure, appearing as an 8 in. circular blotch
of light with a radial pattern of filaments and a mottled central area.
All these highlight-patterns seemed identical, and were floating at
various depths within the car hood.

The handprints in the above photo might appear to be on the surface
of the hood, but in real life they look holographic and seem to
float about one foot deep within the surface of the hood. Appears
like white fishes in a dark pond.

With a start I suddenly I realized what I was seeing. It was incredible:
each highlight was in the shape of a wool polishing mit, with matted
fibers in the center surrounded by outwards-pointing wooly filaments! The
matted part was in the shape of a human hand! There were several of them
floating at various depths all over the car hood, with some of them even
floating in space *above* the hood. They had been invisible to me, but
then they weren’t.

Science is perception!

It wasn’t long before I had half the optosensor engineering department out
there acting like fools, moving their heads back and forth in front of
this black station wagon. I searched through the rest of the sunlit
parking lot and found several other cars with glowing distorted handprints
deep within various surfaces. Once you realized they were handprints, the
shape was unmistakable.

Closeup of handprint pattern, 6″ virtual depth

I proposed several crude theories to explain the phenomena, as well as
numerous hoaxes which could be done via Elvis-shaped polishing mitts to
encode miraculous images onto everyday objects. (The Hood of Turin?) It
was about a week before I figured out what was really going on. The
images were naturally-occurring holograms. The owner of the car had
obviously polished the hood with a dirty lambswool mitt, and the millions
of
particles of grit in the mitt traced out millions of nearly-parallel
scratches in the black paint. The particular hand motion had created a
geometry of abrasion patterns which turn out to be nearly identical to the
interference patterns which make up those embossed-foil whitelight
Benton rainbow holograms.

But there was something extremely weird going on here (I mean even
more weird than hood scratches causing images!) These scratches have
random spacing. They seemed to be functioning as holograms without the
benefit of optical interference. This is impossible of course, since
holography is completely based upon interference effects. However, the
“Rainbow”
hologram technique invented by Benton at MIT allows a
hologram
to function regardless of illumination frequency. The optical bench for
the classic single-stage “Rainbow” holography setup includes a horizontal
slit which produces relatively large horizontal swatches of fine-line
interference patterns on the film (figure A above.) The recorded
interference pattern encodes the depth information as variations in
orientation of the fringes across the stripe. In Benton’s Rainbow
Holograms, only the fringe orientation is important. The fringe
spacing (wavelength) is not. Once I was clued in by the existence of the
car-hood holograms, I realized that I could interpret Benton’s white-light
technique as allowing holograms to function regardless of *fringe
spacing.* Frequency-independence leads to size-independence of fringes,
figure B above. Nobody seems to realize that a Rainbow Hologram will
still function even when the spacing of its fr