Instructions: Polarizing Viewer

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gloved hands manipulating a polarizing viewer with a negative inside showing a rainbow effect

Identification

  • This non-destructive test can be used to determine if a negative is either cellulose acetate or cellulose nitrate rather than polyester.
  • Note this test can not differentiate between cellulose acetate and nitrate bases.

Materials and Tools

Materials

  • clear double-sided tape
  • 2-ply mat board, Photographic Activity Test (PAT)Footnote 1 approved
  • two polarizing filters/films (H10.5 x W10.5 cm)

Tools

  • scissors
  • ruler
  • Exacto knife or mat cutter
Materials and tools

Measuring and Cutting

  1. Cut four pieces of mat board to external dimensions: H 18 x W 18 cm
  2. Cut four inside windows within centre: H 9 x W 9 cm
  3. Cut two polarizing filters/films: H 10.5 x W 10.5 cm
four mat boards with cutted-out centers and two polarizing films as described in steps 1 to 3

Assembling

  1. On two mat boards, place a piece of clear double-sided tape above each side of the centre openings.
  2. On two mat boards, place the polarizing filter/film on the double-sided tape to cover the centre opening.
  3. Tape the two mat boards with the polarizing filters/film to the two remaining mat boards.
  4. Together these make the polarizing viewer.
two assembled mat boards with polarizing films and double-sided tape as described in steps 1 to 4

Orientation / Complete Polarizing Viewer

  1. Place the two mat boards with filters on top of each other. If the filters/films are transparent, they are not polarized.
  2. Turn one mat board with filter 90 degrees.
  3. If the filters/films are opaque or black, they are successfully polarized.
gloved hands superimposing and pivoting two assembled mat boards with polarizing films as described in steps 1 to 3

Identification with Polarizing Viewer

  1. Using gloves to handle the negative, place it between the two polarizing filters/films that are in polarized orientation.
  2. Hold the polarizing viewer firmly together to prevent the negative from slipping out.
  3. Observe the thinnest possible density of the negative through the polarizing viewer (the outer clear edge is a good choice) while gradually tilting it.
gloved hands manipulating a polarizing viewer with a negative inside as described in steps 1 to 3
  1. If a rainbowFootnote 2 pattern becomes visible, then the negative support is polyester.
  2. If no rainbow colours are visible and the polarizing filter/ film remains black, then the negative is on an acetate support.
gloved hands manipulating a polarizing viewer with a negative inside showing a black or rainbow effect as described in steps 4 and 5

Bibliography

National Parks Service. Completing the Polarization Test: How to Make and Use a Film Viewer.

Bennett, Karen L. and Jessica S. Johnson. “Identification of Film-Base Photographic Media,” National Parks Service Conserve O Gram, No. 14/9, 1999.

Fischer, Monique C. and Andrew Robb. “Guidelines for Care and Identification of Film-Base Photographic Materials,” Topics in Photographic Conservation, American Institute of Conservation. Vol. 5, 1993.

Fischer, Monique. “A Short Guide to Film-Based Photographic Materials: Identification, Care and Duplication,” NEDCC Technical Leaflet, updated 7/2012.

Reilly, James. The IPI Storage Guide for Acetate Film. Rochester, New York: Image Permanence Institute, Rochester Institute of Technology, 1993.

Acknowledgements

Tania Passafiume
Head Conservator of Photographic Materials

Carla Klück
Digitization Project Co-ordinator (acting)

Anna Lehn
English Editor

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