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Cool trick of the light on a hot sunny day

July 3, 2016


Friday (July 1) was the first time that I’ve seen reflected light project a “photographic” image from the surface of a shiny aluminum can onto dry concrete.

It’s not unusual in direct sunlight for a curved and polished aluminum object to throw off abstract specular highlights and prismatic effects. Likewise, very bright light can project a colour shadow of a glass bottle on the ground. And, of course, an object can be reflected by the surface it sits on to the degree that the surface is reflective.

None of that, at first glance, explains what I saw on Friday. Bright sunlight was bouncing off the aluminum can and casting a kind of conical or azimuthal projection around the base of the can. Surprisingly, this projection included a  readable reversed image of the text that was printed on the can: “Club Soda”.

Before I put forward my explanation of this unusual trick of the light, I should add that it was only visible the way that I first found the can—within a bit of partial shadow cast by a metal bracket on the side of the clapboard-clad building.

Moving the can away from this one spot—whether out of the shadow or into deeper shadow—and the visible text vanished from the projection of light around the base of the can.

Colour me puzzled,  if only briefly

The light passes through the translucent ink, and reflects of the opaque background back through the blue ink as through coloured glass.

Light passes through the translucent ink layer; reflects off the opaque background and back through the ink as if it were coloured glass.

The effect that I think I was seeing was basically the same as when bright light passes through a coloured glass wine bottle and casts a glass-coloured shadow.

In this case, however, the “glass” was no thicker than a layer of printing ink.

While I never had the opportunity as a graphic designer to prepare art for an aluminum can, my understanding is that the printing process is materially similar to the flexography process used to print on aluminized Mylar packaging, which I am somewhat familiar with.

Exactly as in flexo printing, the empty club soda can that I saw on Friday used a number of translucent spot colour inks: red, blue and black as well as one opaque ink: white. With these inks, at least three basic effects can be achieved on aluminum:

Where there is no ink, the shiny metallic aluminum shows. Where a translucent ink is printed directly on the aluminum, the ink takes on the metallic shine of the can. Where a flat, un-metallic colour is required, a translucent ink is underprinted with opaque white ink.

There may additionally be a lacquer layer over the final printed can.


What I think happened is that the sunlight was intense enough on Friday that a significant amount of it went right through the layers of clear lacquer and translucent blue and black ink and reflected back off the opaque background (either white ink or aluminum can).

At that point, whatever light came bouncing back through the layers of translucent blue and black ink and clear lacquer might as well have been shining through a stained glass window—the effect would’ve been identical.

Like I said though, the reflected text was only visible within the serendipitous half-light of a shadow cast off the wall. Which is to say that this sort of thing probably happens all the time but is just too weak under the conditions to be visible.

Putting the “can” in Canada Day

And yes, I was aware that July 1 was Canada Day. It was exactly 149 years since the Confederation, in 1867, of  the Provinces of Canada, Nova Scotia, and New Brunswick into one big Dominion. Yay!

Don’t think that I didn’t celebrate either. I slept late, caught up on some reading and performed important maintenance on my bike trailer. At 10 p.m. I even stopped to listen to the distant rumble of celebratory fireworks from Canada Place in downtown Vancouver. Click the images to enlarge them.

From → Binning, Fairview

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