Polarized Light Photography for Art Documentation

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Polarized Light Photography eliminates surface reflections and it’s used by professional photographers for high quality documentation of art. The American Institute of Conservation guide to digital photography has in the chapter “Visible Light Photography” a short paragraph on “Polarized Illumination” [1]. This post adds my insights into this method.

 

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Light Polarization

A single particle of light can be imagined as a wave which propagates from its source into space. A beam of light from the sun, an halogen or an LED lamp, is composed of multiple light waves which vibrate in any directions.

Polarized light Photography. Technical photography, paintings conservation, paintings authentication, conservation science, CHSOS, Cultural Heritage Science Open Source, Antonino Cosentino, coins, prints, drawings, stamps, pigments

Light from a bulb or an LED lamp is non-polarized. Light waves vibrate in any direction while propagating from the light source into space.

When we want polarize this light source we put in front of it a polarizing filter which allows through just the light waves vibrating in one specific direction.

Polarized light Photography. Technical photography, paintings conservation, paintings authentication, conservation science, CHSOS, Cultural Heritage Science Open Source, Antonino Cosentino, coins, prints, drawings, stamps, pigments

A Polarizing Filter allows through only the light waves vibrating in a specific direction.

A classical experiment with polarized light is that done with a calcite crystal and a polarizing filter.

 

Why Polarized light for Art Photography?

Our goal is to eliminate glare in our photos of paintings: in particular, those ugly reflections from varnished paintings. This is the trick: Light from the lamps can be Reflected or Diffused from a painting. Reflected light gives ugly glare while diffused light is pleasant. When the light is reflected it keeps its polarization. When the light is diffused it loses any polarization. So, when we send a polarized light onto the painting, the glare  is a polarized beam while diffused light vibrates in any direction.

Polarized light Photography. Technical photography, paintings conservation, paintings authentication, conservation science, CHSOS, Cultural Heritage Science Open Source, Antonino Cosentino, coins, prints, drawings, stamps, pigments

Reflected light keeps its polarization while diffused light vibrate in any direction.

The final step is to add a polarizing filter on our camera and rotate it 90 degree so to extinguish all reflected light.

Polarized light Photography. Technical photography, paintings conservation, paintings authentication, conservation science, CHSOS, Cultural Heritage Science Open Source, Antonino Cosentino, coins, prints, drawings, stamps, pigments

A polarizing Filter on the camera cuts off the reflected light, extinguishing  glare.

See it’s to believe

As usual, we want see some experiments. For this post I used a painting by Domenico Di Mauro, painter of colorful Sicilian traditional carts, currently 99 years young. He still works in his studio which happens to be beside my place. He’s one of the last practicing this craftsmanship.

This is the video:

 

Polarized light Photography. Technical photography, paintings conservation, paintings authentication, conservation science, CHSOS, Cultural Heritage Science Open Source, Antonino Cosentino, coins, prints, drawings, stamps, pigments

Circular filter on camera at 0 degree (Up figure) and 90 degree (Down figure). The Polarized light photograph shows colors much more saturated and glare extinguished. See detail of coin (10 cents of Polish Zloty).

Equipment

Polarizing screens. I recommend those from www.polarization.com. They carry the laminated polarizing sheets, width 17″that I use for my Dowel DP 1000 W lamps, I found 1 feet is enough to cover the lamp.

Circular Polarizing filter for the camera. Don’t use a linear polarizing filter for the camera.

Linear Polarizing Filter VS Circular Polarizing Filter

If you do manual focus you can still use a linear polarizing filter. You need a circular polarizing filter when you work in auto focus. Indeed, the focusing system of the camera  gets hard time to focus when it receives polarized light. The circular polarizing filter resolves this problem. It is essentially a liner polarizing filter that diffuse the polarized light just before feeding it to the camera.

A video on linear polarizing filter and circular polarizing filter:

References

[1] The AIC guide to digital photography and conservation documentation – second edition, Jeffrey Warda editor, American Institute for Conservation, 2012.

 

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2016-10-17T16:34:45+00:00

2 Comments

  1. Dominique February 16, 2017 at 12:43 pm - Reply

    Hi,
    So, what is the best solution when having linear pol filters in front of flashes… with linear filter, or circular in front of lens ?

    • Antonino Cosentino February 16, 2017 at 6:14 pm - Reply

      Hi Dominique,
      The same logic is applied to flashes. They are the same as continuous lighting (such as halogen lamps) when it comes to polarizing filters. So, just set up your experiment as you would do with halogen lamp (linear polarizer on the lamp / flash) and circular polarizer on the camera.

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